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SEEING SOUND With A Home-Made Oscillograph

by MAXWELL R. GRANT

Hooked up to the loudspeaker terminals of a radio this device converts music into rhythmic light rays.

FASCINATING mysteries of sound can be explored with a simple oscillograph made from junk-box parts. Plugged into your radio set, it will convert programs into wiggling lines of light, moving across a screen. The human voice may be “seen” as it is projected upon the wall, and any sound may be virtually put under the microscope for analysis. The instrument described below was designed by J. E. Hoover, a Venice, California teacher, who found it a useful tool for demonstrating the principles of sound to his physics classes.

At one end of a 12xl6-inch panel board, place an old loudspeaker unit. Directly in front of it, five inches away, place a post to carry an adjusting screw and small tension spring.

A shaft about an inch long, mounted in jewelled or cone bearings, should be placed midway between the diaphragm and the spring post. An old clock escapement can be used for this.

Three-fourths of an inch from the end of the shaft, fix securely a reflecting mirror about an eighth of an inch square.

Fasten one end of a silk thread to the center of the diaphragm. Secure the other end to the tension spring after passing it once around the small shaft.

In one end of a metal cylinder about 1/2 x 3/4-inch, place a flashlight bulb and socket. An old automobile dashlight may be used, but it must be closed so that light can escape only through a 1/32-inch hole drilled through one wall, half an inch from the top. Mount the cylinder or dashlight on the panel in such a manner that light emitted through the hole will fall upon the mirror.

A lens about 1-1/2 inches in diameter must be fastened to the panel in such a position that rays from the bulb will be reflected through the lens by the small mirror. Any lens will do so long as it has a focal length of several inches—long enough to bring rays of light from the dash bulbs to a focus upon the revolving mirror.

Fashion four mirrors, each 1% inches square, into a box and mount it securely on the shaft of an old clock. The clock must be securely mounted on the panel so there is no vibration and the mirrors must run true without wobble. Speed of the mechanism can be controlled by attaching a fan blade to one of the shafts of the clock to form a governor. This fan may be fashioned from any light strap metal.

By the rotation of the mirrors, the light reflected from the flashlight bulb is thrown upon a screen a few feet away. The screen may be a piece of paper tacked to a drawing board. If sensitized paper is substituted and the instrument used in a dark room, a photograph record may be made. Simply expose the paper for the desired interval of time, then develop it like an ordinary snap-shot print.

The oscillograph is connected to the loudspeaker terminals of any radio employing a magnetic type speaker or to the plate prongs of the two output on a more modern receiver. Where the receiver uses but a single output tube connect one lead to the plate prong of the tube and the other to the set chassis.

TIN CAN JEWELS
AUTHENTIC copies of European crown jewels, in tin and glass, are the hobby of Dick Stier of Bloomfield, N. J. Stier, himself of noble German descent, got on the kick watching the coronation of Elizabeth II, now has crown jewels of the czars, the Pope, German royalty—all meticulously copied in fruit can metal and junk gems.

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Winners in NEW USE for Old Fords Contest

MODERN MECHANICS pays $10 for every acceptable photo and description of the odd uses to which old Tin Lizzies have been put. The machines shown below are all made from old Model T Fords.

DOWN at Iowa Park, Texas, is an old flivver motor which is enjoying a ripe old age puffing and grunting on half her lungs while the other half supply fresh ozone for tires which have lost the courage of their convictions.

The front two cylinders have been manifolded off from the rest of the motor by the simple expedient of hack-sawing them off where they were not needed, and bunging the ends with welded plate iron.

The intake valves of the rear pair of cylinders were loaded with springs to keep them depressed, and the exhaust valves were brazed in tightly. The spark plug hole was fitted with half-inch pipe and this in turn led to check valves after the air stream had passed by relief or globe valves installed to care for extra high pressure. Once past the check valves the air was conduced by pipe to a storage tank.

A special boiler full of water was provided for the thermo-siphon system, as doing this kind of work was impossible without some adequate means for cooling. If you don’t think the motor works to pump air, you ought to see the water steam!

This novel use for an old Ford keeps a garage supplied generously with compressed air.

HYBRID STEAM ROLLER OWES ANCESTRY TO HENRY MR. G. H. DACY, one of our readers who lives in Maryland, sends us these two views of crazy but useful wrinkles for making use of old Ford car carcasses.

Down at Augusta, Georgia, there is a country club which has extensive acres of greensward running east- ward from the piazza of the club house. To keep the grass in good condition it is necessary to roll it. These rollers, one of which is shown in the accompanying shot, were made from old Elizabeths of the vintage of Model T. Six were made at the cost of one ordinary tractor. The conversion is a simple one and the machine performs satisfactorily.

SERVICEABLE TRACTOR MADE FROM TIN ELIZABETH ANOTHER Maryland tinkerer put the elements of a tractor around his faithful old brass radiatored Ford. Equipped with sunshades, with gas tank out afront, this flivver is now doing hearty, willing work pulling a disc drag. It is said to be able to pull a “single bottom”—that is, a single plow, with comparative ease. The reader will note that the usual Ford rear axle and housing, together with the usual single spring, are employed to drive the machine. The auto wheels are removed, the frame with the bull wheels put on, and gears intermeshed with the big gear by use of small spur gears on the regular axle.

BARREL STAVE SKIS

IF ONE of your bunch can scare up a barrel, that barrel will furnish staves for a dozen skis. You will see by the diagram that a piece of board is fastened several inches forward of the center of the stave, and that a house slipper is nailed to this board. If you lack a slipper, cut down an old shoe or overshoe. For a more efficient ski, smooth the sole with sandpaper, then rub in linseed oil and polish with floor wax.

If the skis do not rack straight, cut a groove in the bottom of the skis with a routing chisel. Do not rout out too much. A groove about 1/4-inch wide and 1/4-inch deep will do nicely to pack the snow under the ski and hold the user on his course.

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Build This Monorail Bathing Chute for Thrills

As a thrill producer, it will be hard to beat this monorail bathing chute. Erected on a hill sloping down to a beach, it will send you flying out into the water at a breathtaking speed. Construction is very simple.

BATHING weather prompts many novel means of sport in the water such as diving slides, swings, etc., but here is a regular “shoot the chute” in simplified form with which loads of sport can be obtained and all at a minimum cost.

In laying out plans for the chute try and find a spot of land with a long gradual dip towards the bathing beach or swimming hole. Several hundred feet will furnish the greatest amount of fun, but it should have a hundred-foot stretch at least.

The track can be constructed entirely of ordinary hemlock or spruce boards six inches wide and 7/8 inches thick. The accompanying sketches show just how to put it together. Use short lengths of board laid end to end, the joints meeting over posts sunk into the ground at the proper height to give the track a nice even bearing to the slider.

The next task is to lay the rails on the track. These consist of a single line of spruce “furring” three inches wide laid down the exact middle of the track and nailed tightly to it. Rail joints should never come over any track joint, but the furring should be laid over it as shown, leaving l-1/2 inches of track exposed on each side of the rail. The final dip should be either down a steep bank or over a short trestle arranged to gain the incline. Then build the final sweep so it curves sharply upward to the end or “take off.”

The slider is very easy to construct. Cut off two pieces of three-inch furring 3 ft. 6 in. long and lay parallel 3-1/2 in. apart. Connect the front end by a piece of 4×4 timber 15 in. long split diagonally down its length as illustrated. Then connect the rear ends of the parallel strips by a board 12 in. square for the seat. On top of this fasten a cushion made of heavy canvas and stuffed with ground cork taken from a grape keg. Two handles are arranged as shown.

Turn the slider over and then attach four hard wood blocks to the under side of the parallel strips as shown, two at the front and two near the rear end. Set them back slightly from the inside edges and fasten with long screws driven in from the top. Then shoe each block with smooth iron, countersinking all screw heads. When completed, give all but the cushion and iron runners several coats of good paint. Then attach a piece of sheet steel under the footrest and curve it slightly to act as a guard to ride over any protruding joints of the track.

Now go over the track thoroughly, driving down any projecting nailheads and smoothing off knots, slivers, or any projections that might cause interference. Give the entire structure two or three coats of linseed oil, and after it is dry wipe the entire surface of track and rail with candle stubs. This lubricates the wood and increases the sliding qualities. Shine off the runners of the slider with fine emery paper to make them smooth and then treat the under surfaces with paraffine.

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Mechanical Flying Goose Decorates Radiator Cap

For novelty in radiator ornaments, you’ll have to go a long way to beat this mechanical flying goose. As you speed along in your car, an ingenious arrangement of mechanism in the bird causes it to straighten out and flap its wings to simulate a real live goose in flight.

WHILE your car is standing still this wild goose isn’t so wild. He perches sedately upon the radiator cap surveying the world with a glassy eye. But as soon as you start up and shift into high he flattens out his tail, stretches his neck forward and begins to flap his wings as if he were going somewhere, and going there in a hurry.

There is not a staggering lot of work on this bird, but it is important that all moving parts operate freely. With the exception of small brass rod, a short piece of tubing to fit over it and some sheet duralumin or aluminum, all materials can be picked up in your work shop.

Start with the body. The original was made from a block of sugar pine 1-1/2 in. thick, 2-1/2 in. wide and 4-3/4 in. long. The general shape and inside carving is shown in the underside view in Fig. 1. In hollowing out the body an expansive bit, hack saw and chisel will do the work nicely. A certain amount of fitting will be necessary later when you install the mechanism of neck, wings and tail.

As the wings are first in importance, make and install them before the other parts. The phantom view, Fig. 3, shows how the wings are installed. Cut the wing plane or blade as per the squared diagram, Fig. 3, from sheet duralumin. Tin will do if you have not the lighter material, but it won’t function as smoothly. On the underside secure a section of 3/32 in. brass rod by means of fine wires. You will not be able to solder to duralumin.

Now make a universal joint of a short section of brass tubing soldered to a piece of tin cut as indicated in Fig. 3 for the wing to operate in. This fits into the slot in the side of the body, and is fastened to it by means of the bent ends of the elevating axis driven into the wood. I The principle of operation of the flapping wing is known as “feathering,” and is practically the same as the movements of a sculling oar used at the stern of a boat. This action is illustrated in Fig. 1. Note in the first position that the wing tip is down, but the leading edge is elevated. Thus the air current causes the wing tip to rise. When it reaches the top limit of the second position, or rather while approaching it, the crank arm inside the body is brought against a wood st^p, which tilts the leading edge down, and thus the air current forces the wing tip down again. This flapping operation continues as long as there is a fair wind. The rubber band snaps the wing into proper position as soon as the crank-arm passes the center line.

It is necessary to have the brass rod, or crank-arm shaft, fit nicely in its tube bearing and also to have elevating axis work without much play. Tension of the rubber band will be determined by experiment, as will the location of the wood stops. Bind the rubber bands to the crank-pins with thread and apply model airplane cement also.

Tin will not do for the tail on account of its weight. So large an area must necessarily be above the axis that either duralumin or aluminum must be used. Even at that it must be counterbalanced with a good-sized piece of lead, for this weight must also keep the head erect when at rest, in spite of the fact that the latter, as well as the neck, is made of soft balsa. Added weight can be had by using a fairly heavy wire or brass rod for the connecting link, as illustrated in Fig. 2. It is necessary to swing this link low to clear the wing mechanism. Light piano wire is used for the link between head and body. This is a necessary feature, for otherwise the head would merely lop down in lifeless fashion when the neck is pushed forward. Loops in the piano wire are made by twisting two or three turns around a small nail driven into the workbench.

Use pins or long brads for the axes of head and neck, and be sure the holes are large enough for the parts to move freely. A neat counterbalance weight for the tail is made by rolling a cylindrical piece of lead in an extension of the former, as shown in the drawings. When air currents force the tail to a horizontal position this weight moves up into a recess of the body shown in Fig. 1. Set your goose on a standard of galvanized wire to clip around the radiator cap, and give it a try-out before painting. If the wings flap too high or too low, or both, make the necessary adjustment by using thicker wood stops. You may need to change the tension of the rubber bands for smoother action.

After tests are made, by all means give your goose the very best paint job you know how. Give all wood parts a white ground-coat, and sandpaper smoothly when dry. The bird should, of course, be taken apart for the painting. Next, with a comparatively dry brush—that is, without paint dripping from it—touch in the brown feathers until only the wing tips are left white. Also leave the breast white, as well as the underpart of the body, a portion of the neck and a spot on the side of the head, as shown in Fig. 3. Black, glass-headed pins cut off to about 1/4 in. are used for eyes, and they certainly give this lively fowl a determined look.

With a first rate paint job this radiator ornament will cause much comment.

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Approval Meter

BY SAMUEL KAUFMAN

WITH the “approval meter,” program directors will no longer have to rely on laughter, applause or boos to learn just what the audience thinks of entertainment.

The method—developed by Schwerin Research Corporation—works automatically and records reaction for study later. All you do is push or pull a tiny lever at your side.

At present, tests involve the assembling of two groups of 300 listeners in a Radio City studio each week. Recordings of past programs (or transcriptions of auditioned programs) are played back. During each program segment, a number is flashed on a screen and the participants vote on whether they like, or dislike or are indifferent to the program at that point.

The approval meter instantly records each participant’s responses on an individual card. A tiny control lever on the right arm of each studio seat is manipulated to punch a card which is later filed and tabulated automatically by an office machine. When the listener pushes the lever forward, he approves of the program.

When the lever is moved back, he registers disapproval. And when it is kept in neutral position, it shows the indifference of the listener at that point.

The control lever, mounted on top of a small flat box attached to the seat arms, is a single-pole type of throw-switch similar to that used on small telephone switchboards. Placed conveniently for constant manipulation by the participant, the lever controls signal impulses which are relayed either to the stage or a backstage room where the participant’s likes and dislikes are recorded.

A master timing device linked to each lever control box permits a hole to be punched at every 12-second interval. This time-unit, however, is arbitrary, and can be adjusted to any desired length.

A graph chart is set up later for program directors, advertising agency men and other parties interested in the survey re- suits. The chart is marked off, left to right, in numerals designating minutes. Then, the same recording voted on by the test audience is played back.

Careful selection and pairing of turntable and chart motors assure adequate synchronization. Variations between -the turntable speed and the mechanical pointer’s rate of motion have been so slight as to be considered negligible. However, Schwerin’s engineers are prepared to employ a common motor for both the turntable and the chart should any synchronization difficulties arise.

Consumer polls are being used today in virtually every industry to determine the opinions of the public on various products and commercial services. Inventive genius has contributed much to the successful handling of such “sampling” polls, much of the work being done by mechanical and electronic means.

Customary office equipment such as telephones, typewriters, calculating machines and dictaphones have been used in such polls for a long time. But Schwerin’s is the first device especially designed for the efficient registering and exhibiting of public preferences.

Although the approval meter shown here was primarily designed for radio, the method is applicable to any entertainment.

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“Perpetual Motion” Machine Makes Novel Window Display

For novelty in window displays you can’t beat this “perpetual motion machine” as a means of attracting the attention of passers-by. Powered by magnets concealed in the tracks, the steel ball whirls round and round, bewildering those who pause to watch.

SCORES of people will walk right by an artistically decorated store window without giving the display a glance. On the other hand, another store window with a novel display catches the eye of every passer-by.

An unusual novelty, particularly if it is puzzling and mysterious, will attract and hold more attention than a $100,000 painting by a 16th century master.

The reason for the attraction is this: Movement always arrests the eye. Herewith is described a window display novelty which always commands attention. Not only once, but time and again. It consists of a device suggestive of the ever elusive phenomenon: “Perpetual Motion.” Unlike many of the so-called “perpetual motion machines,” it has no gears, belts or levers. It consists simply of a polished steel ball rolling “perpetually” around a circular track.

Suspended above the track is what appears to be a huge permanent magnet, which is for illusory effect only. The device makes a very puzzling illusion. The ball rolls about 30 miles in 24 hours, while an indicator records the mileage. Passers-by will pause time and again to see how many miles the ball has traveled.

Figure 1 gives the general appearance of this device. The tracks are made of %” strips of brass mounted on a circular wooden base 42″ in diameter. A 4-inch steel* ball rolls on the track. The base is mounted on six clear glass bottles which serve, apparently, to insulate the device from the ground. Suspended centrally over the assembly is what appears to be a 30-inch permanent magnet. The ball rolls counter-clockwise around the track about 10 laps a minute. Every turn it trips the level of an indicator which registers the miles covered.

What makes the ball roll? Electro-magnets concealed under the track. How do they get their operating current? Through two bottles rilled with acid solution which makes them conductive. The current is supplied by a six volt storage battery or by a small transformer such as is used for operating electric trains. The metal ball makes electric contacts across the rails in such a manner that the electro-magnet immediately ahead of the ball is always magnetized. As soon as the ball comes over the center of the magnetic field of that magnet, the contact is broken and made again with the next magnet ahead. While the pull of each magnet is very slight, only a very little effort is required to keep the ball moving. If the ball is true, and the tracks smooth and level, practically the only resistance is air friction. Two amperes at six volts will operate the device.

Figs. 3 and 4 illustrate the principal features of the construction. First, a wooden ring 42″ in outer diameter, 4-1/2″ wide, and 3/4″ thick must be made. It is best to build this up of three laminations of 1/4-inch wood. However, various forms of “plaster-board’”

or “wall-board” can be used equally well. The ring is laid off in 40 equal spaces, and 40 rectangular holes 3/4″x2-1/4″ are cut through the ring, as illustrated in Fig. 3.

The electro-magnet assemblies must next be made. Figure 4 shows their construction. The cross-ties, which serve to hold the magnets and the brass rails, are made of wood. Maple is Recommended because it does not split easily. The slots for the rails are cut with a hack-saw blade. The rails should fit tightly in the slots. Note that a 1/4 in. hole is bored vertically through the cross-tie adjacent to the inner rail slot. This is for the purpose of cutting the inner rail with a fretsaw later.

The cores of the electro-magnets can be cut from solid pieces of soft steel, but their magnetic property is improved by making them of laminated construction from 3/32-in. sheet steel. A large number of the pieces can be shaped at once by clamping them in the vise and using a saw, chisel and file. The finished plates are grouped to form the core, and are wrapped with about 100 windings of No. 32 enamel insulated copper wire. One of the ends connects to the inner rail section immediately to the left of the magnet. The other connects to a common return wire to the battery.

After all the magnet assemblies are prepared, they are placed in the holes in the ring base and wired up as shown. The brass strips for the rails are pressed firmly into the slots. Then a fret-saw blade is passed through the vertical holes in the cross-ties, and the inner rail is cut into 40 sections. Each section should be tested for a short circuit. The device is now connected temporarily to the battery, one wire leading to the common return wire, the other to the outer rail. The steel ball is placed on the track and given a little start in a counter-clockwise direction. It keeps on rolling! In fact, it may gain sufficient speed to “jump the track.” A resistance should be installed in the circuit to regulate the speed.

After the tests have proved satisfactory, the rest of the work consists in “dolling up” and camouflaging. A circular, wooden ring 1/4-in. thick is nailed to the bottom to hide the magnets and the wiring. Two brass bolts project slightly from the bottom, to connect with the lead terminals in the corks of the bottles filled with acid solution. Of course, provision will have been made that these bolts connect with the common return wire and with the outer rail respectively, as illustrated in Fig. 2.

The tracks and the magnets are coated heavily with melted paraffin. Then very viscous plaster of paris is poured between the rails. Before setting, this is molded into the form shown in cross-section view in Fig. 2. Afterwards it is well to paint it some dark color. The visible presence of plaster of paris immediately suggests concealment.

Figure 4 shows the construction of the camouflage magnet, and suggests a means of obtaining a true rolling ball. A governor ball from an old steam engine may be picked up at a junk-yard and will serve the purpose very well. The 4-in. dimension is not essential.

The mileage indicator is mostly for psychological effect, but may be dispensed with. Curious passers-by will stop daily to see how many miles the ball has traveled. New signs will greet their eyes. With very little trouble, a mileage indicator from a bicycle can be remodeled to serve the purpose.

This “perpetual motion machine” compels intention. It is an excellent advertising attraction for any store window. Few passers-by are artists; every passer-by is curious.

The device will attract considerable attention to any display or signs set up in your window along with it. While watching the ball their eyes will fall on the signs.

SWAMI

As mystifying as the Indian rope trick, this magic marvel defies the laws of gravity.

PROBABLY Isaac Newton was right; but you couldn’t prove it with this gadget. It just seems to work contrary to all laws of gravity.

Swami, by itself, reacts like any other object: supported at one end only—it falls. But, add a fairly heavy belt, as shown in the photo, and it will not only stay up but actually take quite a bit of extra pressure to make it tilt down, even slightly.

We won’t tell you how or why it works. That is part of the mystery. Go ahead and make one and try to find out for yourself. You’ll be truly amazed.

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Animate Your Photographs

A pull on a string and this photo comes to life. To make this toy choose or make a photograph of your child (or even yourself) in a pose which shows the arms and legs suitably extended. Make two identical enlargements and glue these on thin Masonite or plywood.

Now you have two mounted prints; on one you will want to use only the torso, so mark off the legs and arms. On the other print you will want to use the limbs with some additional material left on the upper ends to allow for pivoting. Next cut out these areas with a coping saw. Drill holes into the tops of the arms and legs to accommodate loose fitting nails, insert small washers and attach screw eyes into the ends of the limbs (see photo). Now hammer the arms and legs into the body into their proper positions. The limbs must be free to pivot. Finally, tie the strings as shown in photo. A screw eye can be attached at the head to facilitate hanging. To operate merely pull down on the string. You’ll have loads of fun. Don’t overlook the possibilities of commercializing on this toy in your spare time. I’ve sold many to eager parents.—Ro Capotosto •

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Easter-Egg Zoo

BERTHE MARCHAND used her ingenuity. Needing something original for the Easter table—something for the children to admire—she hit on the idea of making an entire zoo of animals, using colored Easter eggs and other odd bits of material easily obtained for a few cents at any stationer’s.

Why don’t you do the same? It just takes patience, nimble fingers, and extreme care in handling the eggs— which can be dropped only once.
(Maybe you’d better boil them.)

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“Poor Man’s” Yacht

This floating dream-home will allow you to cruise the river in millionaire style.

By Rudy Arnold

HAVE YOU ever dreamed of cruising down the river in your own private yacht? If you have, now is the time to do it and enjoy the plushness of a modern dream-home complete with front and back yard.

Wesley H. Dyer’s “Dumbo” has made a low-cost family yacht a practical reality for the water-loving landlubber. Dyer, president of the Metal Products Company of Nashville, Tenn., named his original family yacht, shown on these pages, after Walt Disney’s flying elephant because his novel craft was big but surprisingly agile for its size.

In recent years the forming of numerous lakes in Tennessee and Kentucky—like the Kentucky Lake, largest man-made body of water in America— by the building of large dams stirred up a lot of excitement about family boats in the area. Dyer heard people talking about big, comfortable boats that had all the space and accommodations of a home, as well as absolute safety.

The more conservative citizens of Nashville laughed when they heard that Dyer was going to take the plunge and build land-locked boats. They chalked off his idea as a silly delusion. Besides, they said, it would take a millionaire’s income to afford a dream boat capable of transporting an entire family in such handsome style for a holiday week-end or the summer.

Dyer set out to see if he couldn’t make a real houseboat that would give the new lake dwellers exactly what they wanted. He recalled that he had made special pontoons for many military uses during World War II. He talked to his chief engineer, Charlie Mager, about designing an inexpensive but spacious yacht with an auto trailer as the cabin.

The two men decided the best way to build the hull was to put it together in pontoon sections so that the family yacht could be constructed to fit the size of the family pocketbook. It would take eight sections bolted together, each holding three 55-gallon oil drums, to make a 16×24-foot hull able to float a 16-foot housetrailer.

If you supply your own oil drums, each section would cost $45. With $35 for deck lumber this would make the basic boat cost only $395. The same layout with special pontoons supplied would cost $60 per section. Add to this the $35 for the deck lumber and you get a total of $515 for this unique craft.

For Dyer’s original experimental Dumbo he* used 19 pontoon sections bolted together to form a barge 15 feet wide and 40 feet long on which he placed a 23-foot Mid-State housetrailer.

Each pontoon section has an angle member on either side of the bottom and channel members on both sides of the top. These members are bolted to three steel pontoons 25^x42 inches long and 15 inches deep. Together with the angle frame at each end they form a pontoon section 3 feet, 6 inches wide by 8 feet long and 18 inches deep. Each section supports 100 pounds for each inch of submersion. The entire unit will support 1,900 pounds for every inch of water it draws.

Dyer made up the steel pontoons in these sections from 18-gauge cold-rolled steel. He then had the metal rustproofed with a zinc phosphate coating inside and out. They were then tested with two pounds of air pressure to check against possible leaks and sprayed with an oil mist on the inside. For further anti-corrosion treatment he had all parts painted with Navy specification zinc chromate primer. The bolts are all cadmium plated.

On the forward end Dumbo has a false bow which is not essential to the boat. For the power plant there are motor mounts for two outboards at the stern. Instead of a rudder, the mounts are set near the sides of the vessel. By controlling the engine speeds of each motor Dyer can steer his craft from the flying bridge with greater flexibility than a rudder-guided motorboat and can turn his ship around in almost its own length at any running speed—an impossible stunt for a conventional yacht.

The Dumbo’s skipper can sail the housetrailer from the flying bridge. Once the outboards are firing, you can refuel the family yacht under way without stopping from two five-gallon tanks hung under the flying bridge.

A storage battery powers the navigation lights. Under the flying bridge on the deck is the trailer’s gasoline-powered generating plant for interior and running lights and for powering the water pressure unit for the modern kitchen and shower bathroom.

In its trial run up the Cumberland River through Tennessee and Kentucky into the Ohio River, Dyer deliberately navigated close to giant tugs to test the structural rigidity and seaworthiness. The Dumbo rode the waves like a duck on a midsummer millpond. Strong winds had very little effect on the yacht’s handling. On the maiden voyage Dumbo covered 271 miles from Nashville to Paris Landing on Kentucky Lake in 71 hours.

Dyer recently discontinued the original Dumbo for an improved version he devised with an all-steel hull with four watertight compartments 13 feet wide, 46 feet long and 30 inches deep.

He has already had the last laugh on those who scoffed at his idea and the boating fraternity got their dream—at a price that they could afford. •

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Interesting Experiments with Air Currents

by C. FRANCIS JENKINS – Famous Inventor

You’ve seen flags flutter in the breeze, watched airplanes fly, read of buildings which collapsed from the inside out in tornadoes—but do you understand the cause of these phenomena? Mr. Jenkins, famous for his inventions in the field of television and inventor of the movie projector, has devised a number of fascinating experiments to test the behavior of air currents. Try them for yourself, as explained below, and you’ll have a better knowledge of why airplanes fly and why gliders glide.

WHY does Old Glory flutter in the breeze ? Why doesn’t it stand out straight from its staff like a piece of tin? A flag does not flutter in water. So where does the flutter come from?

If you can find the answer to that you are on the trail of why airplanes fly, why birds and gliders glide, why buildings collapse in tornadoes, why strong wind breaks plate glass windows outward instead of blowing them in, why the ball dances on top of the water stream in the fountain, why baseball pitchers throw curve balls, why streams in flood crest in the center, why logs are sucked out to ride the crest, why the lamp flame is drawn toward the open window—in fact you are on the trail of the unusual of usual happenings.

Emerson said “That is ever the difference between the wise and the unwise; the latter wonders at what is unusual; the wise man wonders at the usual.”

Yet if you start hunting through books for an explanation of why the flag flutters the only one you will find, that I can recall, is one I discovered many years ago in “Alice in Wonderland,” where she tells us that the Old-Man-in-the-Mountain supplied flutters for flags, rustles for silk dresses, and a very superior quality of post hole.

Obviously that isn’t a very satisfactory explanation, so I have drafted a simple explanation into a physical law which I could apply. In simple words that law is: “Any object free to move in a fluid will move toward that part of the fluid having the swiftest motion.”

That is why the flag flutters, why leaves are “sucked” up from the ground, and that is why buildings are often pulled apart in windstorms.

If you add to that a second law—that air moving at increased velocity is accompanied by decreased pressure— you have the basis for a study of model airplane and glider design, or for the building of big powered planes.

That is the law that explains the increased lift on top of an airplane wing—where a partial vacuum exists—and why that lift increases as the depth of chord, or thickness of the wing, is increased. Put in simple language, when the wing meets the air the current is divided, and some passes under the wing and some over the top. Unless the two streams reach the rear edge at the same time there will be a vacuum behind the wind. But, as the air traveling over the curved top surface has farther to go than the air under the wing, which has a flat bottom surface, the only way it can get to rear on time is to speed up.

If you want a very simple demonstration of the lift of air at high velocity passing over the top curved surface of an airplane wing, hold a sheet of letter paper by two corners before your lips and blow over the top side, which has dropped down to your chest. As you blow the air stream, at increased velocity and decreased pressure, follows down the curved surface of the paper, creates a partial vacuum, and the normal air pressure beneath the paper lifts the sheet upward. You can get an even more pronounced curve in the paper by clamping the end between two books or magazines, and, by blowing hard enough, lift the free end from a vertical to a horizontal position. There are innumerable little tricks with paper that teach the basic facts about moving air currents, their effect on free moving objects, and all have some bearing on flying, and, in particular, gliding and soaring flight.

Take a sheet of letter paper, put a crease across it about four inches from one end, pull the shorter portion over the edge of a desk or table to give it a curve, as shown in the drawings. Lay the sheet on the table, with curved portion away from you, place the fingers on the nearer end, the lips close to the surface, and blow. The air stream, deflected upward and around the curved portion, decreases the pressure there and the air underneath the curve, pressing upward in an effort to get into this swift moving stream, raises the curved paper upward and bends it toward you.

Now take another sheet and crease it down the sides, leaving a space of about 2-1/2 inches between the creases, and draw both sides over the table edge to curve them, as shown in the accompanying photograph. Lay this on the table, blow down the center, and the two sides are forced in toward the central air stream.

Next put the curve in the center of a sheet, as shown. When you hold the nearer end and blow, the air stream, following around the curved surface, to which, because of its decreased pressure, it is held by the outer air pressure, creates a partial vacuum, and the air underneath the curve, trying to get into this fast moving stream, raises the curve and pulls the farther end toward you. But if you put a finger on the opposite end to keep it from moving nothing will happen. Light a short piece of candle and place it beyond this far end, hold the paper down with your finger, and when you blow over the paper you can blow out the candle. But release the farther end, light the candle again, and when you blow, the air stream, instead of reaching the candle, will curve around the paper and come back with it toward you. And the candle flame, you will see, will be drawn toward you, for the air around it is also being drawn into the moving stream.

Nothing illustrates that habit of moving fluids sticking to curved surfaces so well as a little demonstration with a candle, a small rubber, paper or metal tube, and some round object, such as a water glass. Light the candle and place it close to the glass. Hold the end of the tube against the opposite side of the glass and blow. The air stream follows the glass, because at its increased velocity its pressure is less than that of the outer air. And, following around the glass, it blows out the candle on the opposite side. You can get the same effect with a much larger circular object, such as a water pail, or one of those fiber waste-baskets.

Place some half dozen lighted candles in a semi-circle around a water tumbler, with the candles about two or three inches away from the glass. Now, with your tube, blow around the surface of the glass, and watch all the candle flames being “sucked” toward the air stream.

Or put your candle on top of a small box or a pile of books, and blow at the base of the support. The air stream is deflected up the vertical side, the surrounding air is drawn into it, and with the air the candle flame is drawn toward the moving stream.

Another stunt with water glasses and candles is to place three or four glasses in a row, with candles between them and beyond the last glass. If your spacing is proper, the air stream blown on the first glass will go half way around it, put out the candle, pass in the opposite direction half way around the second, put out the candle, and continue on until all four lights are extinguished. In each case at least part of the air stream has reversed its direction of curve in order to continue around the next glass.

Have you ever watched a bird hover on motionless wings, and suddenly, without a single flap, shoot upward in the air? Or read about a motorless glider in Germany climbing more than a mile high on rising air currents, remaining in the air more than fourteen hours, or traveling more than fifty miles across country?

Gliders do marvelous things, but they don’t begin to compare to even the average good gliding birds, such as the gull, the hawk, or the eagle.

These simple experiments with paper and candles were designed to show why airplane, glider and bird wings have a lifting effect in moving air. Here are some of a different type that carry the lesson a bit further.

If you can get one of those light celluloid ping-pong balls, an inch and a half in diameter, you can make it float in the air. All you need is a tube—rubber, metal, or rolled up paper. Hold the ball loosely above the end of the tube and start blowing. As long as your breath holds out the ball will ride on top of the current. Its distance above the tube end will be the point at which the force of gravity trying to pull it down exactly balances the lifting effect on the ball. Now place the ball against the wall and blow against it.

“You can hold the ball against the wall with nothing but an air stream to support it, and if you move the end of the tube the ball will follow around over the wall, always remaining in the center of the air stream.

In the first experiment you might suppose that the pressure of the air stream was supporting the ball, and in the second that the pressure was keeping the ball against the wall. But that doesn’t explain why it should move around to follow the movement of the tube. So the only possible explanation is that the high velocity air stream curving around the surface of the ball has decreased the pressure there, and the outer air, at higher pressure, is being drawn in from all sides.

If you have a vacuum cleaner in your home here is one stunt of my own invention that’s still more remarkable. Remove the dust bag from the vacuum cleaner and place a cardboard mailing tube over the blower outlet. Set the machine so that the tube points upward at a 45-degree angle. With the power of the electric blower you can use a much heavier ball, such as tennis balls.

Start the motor and release the ball in the air stream. It will rise along the stream, just as a bird or a glider rises, until it reaches the point where the force of gravity neutralizes the lifting effect. But, when it reaches that point, instead of falling to the floor it will remain suspended in the air.

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“ICE LIZARD”

by L. B. Robbins

AIR minded, ice-boat and mechanically-inclined fans: here is something to arouse your imagination and ingenuity—an air propelled ice-boat using a washing-machine engine for power and capable of good speed and breath-taking thrills. Let’s build a fleet of these “Ice Lizards” for the height of the skating season and give the populace something to talk about.

The body consists of an outrigger plank 5 feet long, 2 inches thick and 6 inches wide. To this are bolted two pieces of 2×3 finished stock, on edge, fanned out on the outrigger 2 feet, 9 inches. At the stern they are beveled to fit together, and bolted. The length of these 2×3’s should be such as to make the total length of the craft 6 feet, 6 inches over all. The outrigger forms the bow and the pointed end-is the stern.

Next, plank over the body from the bow-to within about 2 feet of the stern, with light matched boards. At the extreme stern end of this deck mount the seat. An old bucket seat from a discarded automobile will be just the thing. In lieu of this get hold of any single driver’s seat from the auto junk-yard and tip it back about as shown, shimming its front edge up with triangular shaped pieces of wood under each side.

The two runners and the rudder are shown in detail. The latter should be made somewhat narrower than the runners to compensate for the additional iron-work below the body. By doing this the body will be supported horizontally on the ice. All three blades can be fashioned from sheet steel and measure 15 inches long. The front and bottom edges must be ground to a V edge and ground sharp. The rudder has a hole drilled somewhat forward and above center to which is pivot-bolted the fork in the bottom end of the rudder post. This latter can be made from 1/2 inch pipe with the top end filed square and drilled for a pin. A rudder post bearing is made from a length of %-inch pipe driven through a hole in the stern joint of the side pieces. Screw two wooden triangles to the top and bottom of this joint and then secure the bearing in place with pipe lock-nuts above and below. The height of the stern above the rudder can be adjusted by the collar adjustment on the rudder post as shown. The tiller is shaped and dimensioned as indicated and cut from flat steel. Drill a small hole in each wing and fashion a square hole in the center to fit and pin over the top of the rudder post.

The runners, as before stated, are the same length as the rudder but wider. To the top edge is bolted a suitable length of channel iron which in turn can be bolted to the under side of the outrigger at each end. These are also V shaped and ground to a sharp edge along the bottom and front.

The steering-bar consists of a piece of hard wood a foot longer than the body at a position in front of the driver’s seat, as shown. It should be pivot-bolted to the center of the body and its ends connected to the tiller by taut drawn steel wire. Small turn-buckles may be inserted if desired, to true up this steering system, as it is important that this be strong and easy operating during speed sailing.

For braking purposes a simple drag is resorted to. This is a boomerang shaped piece of flat bar steel, taped at one end for the handle and the lower end ground to a point to dig into the ice. A slot should be cut in the center of the deck just forward of the seat and an oak block bolted below and to one side. The brake is then pivot-bolted to the block through a hole drilled in its bend. A spiral spring is then inserted between a hole near the point and the under side of the deck to hold the point off the ice. To brake it is only necessary to pull back on the brake handle and the point digs the ice until “lizard” comes to a stop.

Lastly, securely fasten two wooden foot-rests to the under side of the body and below the steering-bar as indicated. This allows the driver to rest his feet on these boards and at the same time press along on one side of the steering-bar or the other and direct the course of the craft.

The power-plant consists of a 1/2 h. p. utility gas engine such as can be taken off of washing-machines, or other home appliances. Any good 1/2-h. p. engine will do so long as it turns up 1,700 to 1,800 r. p. m. These have a kick-starter and the newest models are equipped with starter and battery for a small additional cost. This engine is belted to a reduction pulley and jack-shaft to which is fastened a 4-foot, 4-inch wooden air propeller with a 2-foot, 6-inch pitch.

First choose an oak block 12 inches long by 6 inches wide by 2 inches thick. To the top of this mount two 3/4-inch pillow blocks as indicated and bore a hole in each corner for a 3/4-inch pipe. Bend the four pieces of 3/4-inch pipe in the shape indicated. The feet are threaded to floor flanges and the tops fit up in the corner holes in the oak block with lock-nuts above and below. The finished standard should bring the jack-shaft about 2 feet above the deck and its feet should spread to within a few inches of the sides of the deck. Front clearance of two or three inches should be allowed for the propeller from bow. Bolt the flanges to the deck and the propeller can then be fitted to the front end of the jack-shaft. The V pulleys, jack-shaft and V belting used can be purchased at any chain store selling the popular makes of homecraft power tools. As shown, 3/4-inch shafting is specified throughout.

Bolt the engine to the deck, shimming it up if necessary to fit the belt over the engine and jack-shaft pulleys and then allow it to come back so pulley is reasonably taut before bolting home. As time stretches the belt this slack can be taken up by readjusting the jack-shaft block height by means of the supporting pipe lock-nuts. The engine speed control and switch (as well as electric starter controls in the late models) can be extended back to the driver’s position and fastened in any convenient location. The exhaust should be led aft by a long flexible hose lashed to one side of the body.

If thought necessary, the builder can build a front and side screen wire protection for the propeller. While of low power, it might easily prove dangerous nevertheless and a screen hood would be an added safety factor. Even side, tail and head lights can be added with only a little additional wiring. Your starting battery can be used to provide the lighting power. Thus, night driving over the lake will provide its own thrills.

In starting the “Ice Lizard,” jam the brake into the ice, start the engine and let it warm up. Then release the brake and the craft will pick up speed in a few seconds. Make wide turns and for quick stops cut the engine and jam the brake down hard.

Three or more “Ice Lizards” will provide plenty of ice sport this winter. Pepped-up engines, sharp runners and racing props might enable you to drive the old boat at fancy speed.

STAINLESS CHOPPERS
STEELY SMILE of John Gilpin, village blacksmith of Livingston, Mont., is really friendly although strangers are sometimes awed by it. Gilpin broke a set of store teeth 16 years ago, replaced them with rugged stainless steel.

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Build A Glider-Copter

AN 86-lb. helicopter glider, believed to be the smallest aircraft in the world today, has been developed and flown by Bensen Aircraft Corporation of Raleigh, N. C, for use in engineering tests of lighter-than-man helicopters.

Like soaring gliders and sailplanes, the helicopter glider has no engine; it is towed by a car until it becomes airborne and will stay in the air as long as it is towed or as long as there is sufficient wind to keep its rotor blades turning.

Igor B. Bensen, designer and developer of the craft in this country, calls it a “Gyro-glider” and says it can be controlled in the air with one stick like a helicopter. His firm may undertake to produce the machines commercially, and will make plans and kits available to high school and college students who can build them at home for less than $100. He says they will be excellent for sports flying and pilot training. The miniature craft consists of an air frame of tubular [Continued on page 207] steel from the Bensen “Mid-jet” helicopter, a control stick and two nine-ft. rotor blades. Extremely simple to fly, it cannot stall because it is impossible to stop the rotor blades from turning while it is in the air. The Gyro-glider takes off at a speed of 20 mph, lands at about seven mph, and can lift with ease more than four times its own weight.

Bensen points out that rotary-wing gliders were used by German submarines during World War II for observation purposes. Reeled out over the stern of a sub with an observer-pilot at the controls, these engineless craft were employed to search for Allied convoys from beyond the range of the ordinary periscope.

Bensen, who is a native of Russia, contends that American youth today is discouraged from learning to fly by strict regulations and high costs of private aviation. In European countries the governments try to encourage glider flying for the training of future pilots. It is entirely possible that the Gyro-glider, which can be built cheaply and operated for only the cost of driving the towing vehicle, may help revive the interest of our youth in aviation.

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Simple Electromagnet Does Mystifying Stunt

THE well-known barrel of monkeys could produce no more entertainment than an electromagnetic “circus,” consisting of a powerful solenoid magnet and a number of accessories, that you can construct in an evening.

And besides being a source of fun. such a device is highly instructive, and will serve to clear up many of the mysteries of everyday electricity for you.

The electromagnet or solenoid consists of nothing more than a quantity of insulated wire wound on a spool, and provided with a suitable base, connecting wire and plug.

You can obtain a large wood spool from almost any electric shop that does motor repairing; or perhaps the wire you purchase for the magnet will be on a suitable spool. The one illustrated herewith measures approximately 3-3/4 in. long and 3-1/2 in. across the ends.

Winding the Electromagnet The amount of wire you can use varies within considerable limits. About 3 lbs. of No. 22 enameled, cotton-covered magnet wire will do; or you can use 7 lbs. of No. 20, or 15 lbs. of No. 18 wire.

The larger the wire, the less quickly will the coil overheat. If you have access to a screw-cutting lathe or a coil-winding machine, you can do a neat job, putting the wire on in even layers, with a thickness of oiled cloth tape or other insulating material between layers, as shown in Fig. C.

You can do an equally satisfactory job by hand. A few inches of each end of the “wire should project through holes in one end of the spool.

Mount the coil in a vertical position, on a hollow wood base so that a core can be moved up and down through the hole in the spool. The base illustrated in Fig. 5 has sloping sides, and measures 5 in. high, 5-1/4 in. square at the bottom and 4 in. square at the top.

The spool is attached to it by means of two small bolts passing through holes drilled in the end that has the coil wires projecting from it. Also, there is a large hole in the center of the base, corresponding to that in the spool.

Wiring Up the Magnet The flexible electric cord to which the coil terminals are attached enters the base through a hole in one side, and is kept from slipping out by a knot tied near the end.

The best core consists of a bundle of soft iron wires held together by a wrapping of cloth, cord or other binder. The core should be of such size that it can be moved up and down in the spool hole, yet will remain in any position.

It should be of such length that, when the lower end is resting on the table or other surface supporting the coil base, the top end will be flush with the upper end of the spool.

In the model illustrated, this calls for a core 8-3/4 in. long. Instead of a bundle of iron wire, you can use a length of 1/2-in. steel shafting, as shown in Figs. 3 and 6, with almost equal results.

You can operate the coil directly from the 110-volt, alternating current house-supply line; or, if you find that it overheats rapidly, you can interpose a resistance in series with one of the leads. An electric heater element, suitably protected by a guard of some kind, will serve. A number of direct-current experiments also can be performed, using a 6-volt storage battery as a source of power.

Tricks You Can Do With the Coil Now for some tricks with the coil, using 110-volt A.C. current: The jumping ring is a spectacular and amusing performer. Adjust the core so that two-thirds of it projects above the coil, or insert the 2-ft. length of shafting into the hole. Drop over it an aluminum ring—a section of 3/4-in. aluminum tubing an inch or two long will do. as illustrated in Fig. 6.

Turn on the current. The ring will jump up the core and, if it does not fly clear of the core, will bounce up and down in a swing-like manner, finally coming to rest at a point some distance up the core from the coil.

The height attained depends on the weight. A copper ring, consisting of a single loop of copper wire with the ends connected, will do the same thing, but will not climb as high because of its greater weight. The Jumping Ring Trick Now, with the coil current turned on, grasp the aluminum ring in your fingers and hold it down against the coil end. Soon the metal will become warm, and you may find it necessary to let go of it. The energy with which the magnetic force is trying to push the ring away is converted into heat.

With the core end flush with the coil top, lay over it a thick piece of sheet copper as shown in Fig. 6. Turn on the current, and in a short time the copper will become so hot that water, when dropped on it, will sizzle away into steam. It is even possible to fry an egg on this improvised “stove.”

This leads to another interesting stunt. Make a coil by winding, around a bottle or other cylinder an inch in diameter, of 30 to 50 turns of No. 26 insulated magnet wire. Remove the coil from the form, bind it with cord so that it forms a ring, and connect the ends to the terminals of a miniature socket that accommodates a flashlight bulb.

Test the arrangement by bringing the coil near the top of the electromagnet, when the core is all the way down. The lamp should light. If it is too bright, remove some turns from the coil; if too dim, add more.

Secret of the Flashlight Bulb With the coil held snugly against the socket, and the bulb in place, dip the wire and base into melted paraffin, covering everything but the glass bulb. Now, if the paraffined coil is placed in a glass tumbler or beaker of water, and the container is set on top of the electromagnet, the lamp will light, in a manner mystifying to the uninitiated.

Another trick involves a dancing coil. Make a “spring” of fairly fine copper or aluminum wire by winding a dozen turns around a form, and arranging the ends so that they touch each other lightly. Drop the coil over the projecting core of the electromagnet, with the current-turned on. The coil will dance about in a startling manner, with sparks flying from the ends, if everything has been adjusted properly.

You doubtless will work out many more stunts. For instance, you will find that you have the necessary equipment for making 60 cycle noises when a tin can is set on top of the magnet.

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HOW TO TAP A PHONE

By Tony Karp

THERE are many ways to tap a phone; most of them against the law. Our little gadget, however, is quite legal and can be used to great advantage at home or in the office.

Basically, the unit consists of a pickup coil, an amplifier and a speaker. The pickup coil is placed under, or near, any transformer-type telephone without being in physical contact with it. As the electrical currents pass through the phone, part of the energy is induced into the pickup coil. This energy is fed into the amplifier where it is amplified to the point where it will operate the loudspeaker, enabling everyone within range to hear what is being said at the other end of the telephone line. This will come in handy when some relative is calling long-distance; your whole family can hear what he is saying. Or, in the office, the whole staff can hear a salesman’s report. There are other uses for the pickup, limited only by your own imagination.

The unit is a four-transistor audio amplifier with three transformer- coupled stages. The last stage is push-pull for greater clarity and higher output. When idle, it only draws about five milliamperes because the last stage does not draw any current until a signal is applied to it. Yet it has plenty of “sock” and on a good signal will put out over a quarter of a watt, enough to drive the four-inch speaker with plenty of volume. Since the amplifier draws 25 to 35 milliamperes only when there is a signal, the battery will give many hours of use before it needs replacing.

The first step in construction is to drill the holes to mount the chassis and the speaker in the meter case. Remove the decorative moulding on the front of the case. The two holes under the moulding must be drilled or reamed to a half-inch so that the nuts on the volume control and the jack will fit snugly and serve to support the front of the chassis. The case is made of light steel and no trouble in drilling the holes will be encountered if a sharp drill is used. Punch a slight indentation before the hole is started.

Since the amplifier is built in a fairly large case, there is plenty of space for a chassis that will hold all the parts without crowding. An unusual feature is that everything is attached to the chassis. This includes the input jack, the volume control and the battery.

By removing the two nuts holding the brackets in the back, the chassis can be removed intact for servicing.

Before construction of the chassis can be started, the mounting holes for the battery holder, transformers and brackets must be drilled. Using the photo and drawing of the chassis as a guide, lay out the transformers on the chassis and drill holes with a No. 30 drill. The same size holes should be made for the battery holder and brackets; the jack and volume control are mounted under the chassis. Make sure that the brackets for these parts are positioned carefully so that the nut on the volume control and the jack will match up with the two holes in the front of the case.

Next, mount the parts on the chassis. The first stage of the amplifier is mounted at the front of the chassis and the other two follow along the side with the push-pull stage being at the back. Flea clips are used to hold the transistors; they also act as binding posts. As a result, the usual rectangular holes for sockets do not have to be drilled. Three clips are used for each transistor. Mark the flea clip that holds the collector (C) of each transistor with a spot of red nail polish or paint so that you will be sure to connect the transistor with its proper polarity.

Insert the leads of the components into the holes in the chassis. Bend them slightly so they will stay in place. Now you can begin the soldering. Check the schematic carefully as you perform this operation. Be sure that the color coding on the leads of the transformer are correct to avoid oscillation. Another cause of oscillation is neglecting to ground the black lead on the output transformer. Solder this wire to a ground on the chassis and run a wire from there to the speaker. A solder joint on the frame of the speaker will not work. Check also for correct polarity on the electrolytic condensers.

Before testing the amplifier go over the schematic again to be sure that all connections are correct. A few minutes spent checking at this time may save you the trouble of later replacing a transistor.

Slide the chassis into the case so that the nuts pass through the holes in the front and support the chassis. Hold the chassis level and drill two holes for the bolts that will pass through the brackets in the back. Now remove the chassis and insert the transistors in the flea clips, making sure that the collector side is next to the red dot. When you clip the leads of the transistors, leave them a little long; this may save you trouble later. Put the battery into its holder and put on its snaps.

Insert the speaker and grille cloth. Now, install the chassis and bolt it in place. Solder the two leads from the speaker to the two flea clip binding posts on the rear of the chassis. Leave a little slack in these wires so that the chassis can be removed without unsoldering.

Solder the shielded cable from the phone pickup to the miniature plug. The inside wire goes to the short side of the plug, the braided part to the long part. Now the unit is ready to be tested.

Turn the amplifier on. If the unit is functioning correctly, the only sound from the speaker will be the normal hiss generated by the transistors. If the unit oscillates, check the ground on the input, the volume control and the output. If it still oscillates, check the leads on the transformers and be sure that R4 is the right value.

If no sound is heard, check the battery polarity and make sure that the transistors are inserted properly. If this fails to produce results, a check of the schematic against your unit is in order.

Now plug in the phone pickup jack for a final test. Turn on the amplifier and place the pickup coil underneath the base of your telephone. Remember, it must be the kind of telephone which has its transformer in the base and not in a separate box on the wall. In the latter case, the pickup coil of course must be placed near the wall box. At any rate, you should now be in business and all your family or friends will be able to listen in comfort to long distance calls. •

Inflating Toy Balloons With Gas From the City Mains

GAS from the city mains can be used to inflate toy balloons with the simple inflating device shown in the drawing above. Gas as it comes out of the ordinary jet has only a pressure of a couple of pounds behind it, which is quite insufficient for inflating purposes.

Secure an air-tight tin can and fit it with petcocks as indicated in the drawing. Exhaust the can of air by filling it with water, closing the top petcock to prevent air from rushing in when the drain is opened. Now turn on the gas and the water in the can will slowly trickle out, forced by the gas pressure. When the can is full of gas, attach the balloon to the top petcock and then turn on the water supply from the mains. The water will increase the gas pressure to 40 pounds. The water, therefore, must be turned on slowly so that the balloon will not burst from excess pressure.

To fix the shroud lines around the balloon, which are necessary to support the basket, take a board and fix two brads in it, spaced apart to a distance equal to one-sixth the circumference of the balloon when inflated. Blow the balloon up gently with your lips until it is rounded out to the desired size. A third brad is driven into the board above the other two, and this distance equals half the circumference of the balloon. The bottoms of the shroud lines are left long for attaching to the basket.

A paper drinking cup is used for the basket. When the balloon is inflated and its neck tied with silk thread to prevent the gas escaping, fill the basket with half an inch of water and take out a teaspoonful at a time until the balloon rises. When cast loose it will stay low enough in the air so you can observe it for a long time. Before filling with gas, it is best to dip the balloon in talcum powder to prevent scratches from pricking the rubber and puncturing it.

In inflating the balloon, the neck is attached to the petcock through the shroud lines, as illustrated in the drawing. Be sure that the shroud lines are hung evenly so that the lily cup basket is directly under the center of the balloon. This insures an even, steady ascent.

Traveling Woodworking Shop Tours Schools

Making the rounds of schools and playgrounds in Pasadena, Calif., is a complete woodworking shop on wheels. Built on a truck chassis, it includes a circular saw and band saw, lathe, electric drill and small planer. Its power is taken by a long cord from the regular 110-volt circuit of whatever school ground the truck visits. It is equipped for model building and for teaching handicraft work in schools lacking workshops of their own.

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America’s Five Favorite Hobbies

By EDWIN TEALE

AMERICA is the hobby center of the world. More money is spent annually on hobbies in the United States than in any other country on earth. From old-fashioned whittling to polarized-light microscopy, a thousand and one spare-time interests provide Americans with relaxation and amusement. Seeking relief from the strain of an uncertain future, millions of persons, in recent months, have joined the ranks of the hobby-riders.

Supplying the needs of America’s vast army of hobbyists has become big business. Factories with incomes of millions of dollars annually cater to the wants of men and women who are following specialized hobbies. Each week sees an increasing number of hobby columns in newspapers and hobby volumes on the shelves of libraries and bookstores.

Among all these infinitely varied avocations, which are the favorite ones? Which attract the most followers? Which represent the greatest annual money investment ? What are America’s five leading hobbies?

To find answers to these questions, Popular Science Monthly, during recent weeks, has been conducting an extensive survey covering individual hobby groups, manufacturers in the hobby field, national organizations devoted in various ways to the furthering of hobbies. On the basis of the number of persons engaged in the particular avocation and the amount of money spent by them during a year, the following five active hobbies emerged at the top of the list: Photography, Stamps, Music, Model Making, Home Workshop.

Have you ever wondered how many Americans collect stamps or own cameras; how many people have home workshops or spend their leisure time operating model railways? On the pages that follow, you will find such information. For up-to-the-minute facts about the nation’s No. 1 avocation—photography—turn to the next page.

PHOTOGRAPHY – 19,500,000 CAMERAS.

LAST YEAR, 19,000,000 amateur camera ‘fans clicked their shutters 600,000,000 times to record still pictures in the United States. They spent, during that year, more than $100,000,000 for film, supplies, and new equipment. The simple box camera, stand-by of amateurs for decades, is still top seller in American photographic stores. In 1939, the latest year for which such statistics are available, box cameras outsold all other types two to one. Of the 1,500,000 new cameras purchased that year, approximately 1,000,000 were box outfits. Miniature 35-millimeter cameras represent only about one percent of those used by American amateurs. The film most widely in demand is No. 120. Most photographed object in America is reported to be Oscar, polar bear at the Rochester, N. Y., Zoo. Eastman technicians try out new films by photographing Oscar’s white coat against a dark background.

Besides America’s 19,000,000 still-camera fans, there are some 500,000 home-movie enthusiasts. Eight-millimeter movie film outsells 16-millimeter in this field and, in the production of America’s leading maker of home-movie film, the Eastman company, Kodachrome leads black-and-white. More than 200 amateur movie clubs are active in the country. The number of still-camera organizations, counting both junior and adult groups, exceeds 9,000. There are about 5,000 adult clubs and approximately 4,000 school and junior photographic organizations in the country. New clubs are being formed at the rate of more than one a week. Nearly 100 such groups are active in the New York City area alone. There are camera clubs composed of doctors, of chemists, of Wall Street brokers, of telephone-company employes, of bankers, of a hundred and one other specialized groups. The largest photographic organization of the kind is one devoted to snapping railroad pictures. With headquarters in New York City, it has more than 15,000 members scattered in virtually every state in the union as well as in foreign countries. Smallest club is said to be a pictorial group with only eight members, four of which live in New York and four in Cuba. They get together for meetings at intervals of two or three years.

STAMPS – 12,000,000 COLLECTORS.

FIFTY MILLION DOLLARS a year, approximately, are being spent by the 12,000,000 Americans whose hobby is stamp collecting. The number of these enthusiasts, according to philatelic authorities, has zoomed from 2,000,000 in 1931 to six times that number in 1941.

During the Government’s last fiscal year, the Post Office Department sold $4,000,000 worth of new stamps to American collectors. This sum represented an almost clear profit for the Government. In New York City, more than 175,000 school children have stamp collections. Issues from countries overrun by Germany are now in greatest demand. All told, there are more than 150,-000 different kinds of stamps listed.

Many present-day enthusiasts are buying stamps as an investment as well as a hobby. A New York newspaper, a few weeks ago, carried an advertisement reading: “An entire lovely island, south shore, Massachusetts. Will consider exchange for North American stamp collection.” At least 10,000 persons in the United States are following a budget plan of stamp buying to build up college funds for their children. There are, experts say, more than fifteen collections in the United States worth $1,000,000 apiece.

MUSIC – 10,000,000 AMATEURS.

ACCORDING to conservative estimates, 10,000,000 Americans turn to music for a hobby. Musical avocations, during the past decade, have gained rapidly in popularity. In 1932, there were approximately 20,000 school bands in the United States. Now, there are 50,000. In 1932, the number of pianos shipped from American factories was 27,274; last year, it was 136,500.

When the first national high-school band competition was held in Chicago, Ill, in 1923, only 25 bands competed. Today, as many as 5,000 take part in the sectional and national competitions. School orchestras, with an average of about 25 players, number in excess of 40,000. Each year, between 3,000,000 and 5,000,000 school children study some kind of instrumental music. In 1924, when National Music Week was first observed, only 800 communities took part. By 1930, the number had reached 2,000, and by 1940, 3,000.

Shifts in popularity of instruments have occurred in recent years. The once-popular banjo has almost disappeared, while the accordion is riding a new high tide of favor. The finest accordions, costing about $1,000, contain more than 3,500 parts and require six weeks to make.

MODELS – 2,250,000 MODELERS.

THE whine of midget gas engines, the whir of miniature plane propellers, the metallic chatter of model railroad trains provide music to the ears of more than 2,250,000 Americans. Last year, approximately 2,000,000 model airplanes were turned out by amateurs in the United States. Nearly a quarter of them were powered by gasoline engines. The other 1,500,000 depended on conventional rubber-band motors. In recent months, the trend in model-plane building, naturally, has been toward military ships. One eastern amateur has a fleet of 15 gas jobs, each equipped with its own power plant. Similar air-cooled engines are being used in streamlined miniature racing cars. Competitions between these mile-a-minute midgets have increased in popularity during the past year and a half.

In all parts of the country, model railroading is as active as ever. Lumping together the “tinplaters,” who buy their equipment ready-made, and the “model railroaders,” who make theirs to scale, there are approximately 250,000 miniature-train enthusiasts in the United States. Last year, they spent $11,000,000 for new electric trains alone. The average model railroader spends about $3 a week on his hobby. More than 100,000 of these hobbyists are said to have equipment that is worth $400 or more.

HOME WORKSHOP 2,000,000 SHOPS IN 2,000,000 home workshops, American hobbyists are finding fun working with tools and making things of wood and metal. Stemming from one of the most time-honored hobbies of all, whittling, home craftwork has branched out in many directions. Approximately one in four shops, 500,000 out of the 2,000,000 total, are equipped with power tools. According to the estimate of one machinery manufacturer, home-workshop hobbyists in the United States install annually about $5,500,000 worth of new electric-driven machines. Approximately 400,000 of the home-workshop fans are fortunate enough to possess power lathes. The average amount spent in twelve months by the confirmed home workshopper on tools and materials runs between $50 and $100.

Both farm and city dwellers enjoy home workshops. A few years ago, when a leading farm journal made a survey of its readers, it discovered that 27 percent of all the farmers who replied to the questionnaire had home workshops and spent their leisure on craft projects.

Besides woodworking, carving, furniture-making, and metal work, there are numerous specialized branches of home-workshop activity. One of the leading variations of the kind is amateur radio. The 56,000 licensed amateurs in the country construct, operate, and repair their own wireless sets. They range from schoolboys to octogenarians. The youngest is 11 and the oldest 88. One amateur has a layout that cost $25,000 while scores of “ham” operators get along on a total investment of $25. Banded together in The American Radio Relay League, 26,000 of these amateurs help maintain communication when floods or storms interrupt telegraph and telephone service.

ROCKERLESS ROCKER is rigged with two metal strips, wheels for passing time.

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Build this Basketball Scoreboard for your Gym

Spectators at your school or club basketball games will get a bigger kick out of the battle if they can keep an eye on this electric scoreboard, which tells at a glance how the game stands and how much time is left to play. Take the idea to your coach— he’ll welcome it.

by E. A. RERUCHA

THERE is a distinct advantage, from the spectators’ interest standpoint, In having a scoreboard controlled directly from the officials’ table, so that the official score and time left to play can instantly be flashed before the spectators as the game progresses.

The electric scoreboard described in this article is operated by means of a control box from the officials’ table and the score, and other information, is flashed on the board by means of sections of lamps, certain sections of lights in various combinations making up the required number to indicate the score, whatever it may be.

These sections of lights are shown and designated on the wiring diagram in Fig. 3, and are controlled by the toggle switches in the control box. “Minutes to play,” and “quarter” are indicated by illuminating corresponding numbers, which are painted, in white, on the back of frosted glass panels and not visible except when illuminated.

The drawing in Fig. 2 shows an installation of a complete scoreboard ready for use. The conduit containing the control wires leading from the scoreboard to the cut-out box is installed on the surface of the wall and enters the scoreboard case from the side. The method of installation, however, is optional and the conduit may enter from either side or back, and may be concealed in the wall if desired.

Two methods of connecting the flexible cable from the control box to the solid wires in the conduit may be used. If it is possible to install a storing cabinet so that the cable can be coiled up and together with the control box placed in the cabinet when not in use, the flexible cable conductors may be permanently connected to the solid conductors in the cut-out box.

This method was used in the installation shown in the photographs. If, however, it would be desirable to disconnect the control box from the scoreboard, due to lack of available convenient space for the storing cabinet, a cable connector as described in Fig. 1 must be used. This connector is described fully in the drawing. A piece of bakelite panel is supported in the cut-out box by means of two pieces of angle iron fastened to the top and bottom insides of the box by means of No. 6-32-1/2″ machine screws. Phone jacks, one for each of the forty conductors connected to a light, or light section in the scoreboard, are provided, and a binding screw with wing nut for the neutral.

Conductors Connect Through Cut-out Bar The conductors from the scoreboard are connected to the phone jacks and the binding screw on the back side of the bakelite panel and soldered. The front of each row of phone jacks is painted a different color for identification when making the connections.

Conductors 1 to 11 inclusive, are connected to the top row of jacks, beginning with No. 1 at the left end. Conductors 12 to 22 inclusive are connected to the second row, 23 to 33 are connected to the third row, 34 to 40 to the bottom row, and the neutral, No. 41, to the binding screw at lower right of panel.

The flexible conductors running from the connector to the control box are grouped and arranged to correspond to each row of jacks and bound together by means of two straps of leather riveted together between conductors. Each group is marked by painting the leather binding straps of a color to correspond to the color of the row of jacks on the panel to which the conductors in the group are to be connected.

The conductor on the left end of each group should also be marked. A phone cord tip is soldered to the end of each flexible conductor and a terminal lug, as shown in the drawing, to the neutral.

To make connections, the phone tips are simply inserted in their corresponding phone jacks and the lug on the neutral connected to the binding screw. A piece of leather strap with a harness hook is taped securely to the cable and the hook attached to the eye-bolt provided in the bottom of the cut-out box. The purpose of this strap is to support the cable and take up strain.

Construction of the Scoreboard Fig. 4 shows the construction of the scoreboard, which consists of a wooden outside case, completely lined with sheet metal, and a frosted glass window of two large panels, one for the score of each team, and two small panels, one for the time to play and the other for the quarter. The window is hinged to the case at the top so that it may be opened to replace burned lamps. The back of the window frame is also lined with sheet iron. Directly back of the frosted glass panels are the lights for forming the score numbers, and for illuminating the numbers indicating the time left to play and the quarter.

Each light section in the number panels, and also the single lights for indicating time and quarter, are shielded so that the light will not spread, and only that portion of the frosted glass directly in front of each lamp section is illuminated. These shields are fully illustrated in the drawing of Fig. 4. The shields may be riveted or soldered to the sheet metal receptacle panel. Notice also that ventilating holes are provided in the lamp section shields as shown.

The lamps, which are ten-watt sign-lighting lamps, are held in porcelain screw-ring receptacles. These receptacles are attached by making holes in the sheet metal mounting panel (See end view Fig. 4) and inserting the nipple of the receptacle from the back and screwing on the ring from the front.

The lights are connected in sections or groups as shown in the wiring diagram of Fig. 3. It is well to paint each conductor as suggested in the table on the wiring diagram so that they can be readily identified when the final connections are to he made. These colors, however, are merely suggestions, as any combinations may be used.

Lights Hook to Bakelite Terminal Panels A bakelite connection panel is provided between the score number panels and the time and quarter number panels. The conductors from the lights are connected to the back of the binding screws on the panel, which may be No. 6-32, one inch long, brass.

The conductors from the conduit leading to the control box are connected to the front of the panel. The conduit may enter the case from either side, or the back, but must enter on a level with the center of the connecting panel.

The letters of teams’ names are built up of wood strips 1″ wide and 1/4″thick and tacked to a 3/4″ background. The background and letters should be painted in contrasting colors.

The completed name plate is attached to the top of the case by means of four shelf brackets. The letters in “Minutes to Play” and “Quarter” are 2-3/4″ high and built up from strips 1/4″x 3/4″ and tacked to the window frame in the position shown in the drawing of Fig. 2.

To permit cool air to circulate through the ventilating holes provided in the shields and through parts of the case, two-inch holes are provided in the wood case as shown in the drawing of Fig. 4.

If the location of the scoreboard is such so that there is any possibility of the glass being struck by the ball, a guard must be provided. An ordinary wire window guard with an iron frame may be adapted for this purpose, as shown in the view in Fig. 5. The mesh holes of the wire should not be less than two inches.

The control box consists of a wooden box or case, entirely lined with sheet iron, which houses the control switch panel and the cable connections. The construction is fully described in the drawing of Fig. 5.

Small toggle switches, 3 ampere, 110 volts, are used for controlling the lights. From a study of the wiring diagram, it will be seen that by closing a switch, a certain light or a certain light section which it controls, will be illuminated. By closing the proper switches, any numeral may be formed by combining the proper light sections, or any of the lights illuminating the numerals in the panels “Time to Play” and “Quarter” may be switched on or off at will.

It will be noticed that the control switches are all installed on the bakelite panel so that they all turn “on” and “off” in the same direction. The operator can thus tell from the position of the switch levers whether a switch is on or off without having to glance at the scoreboard to see which light sections are illuminated. The light sections or panels are also outlined on the control box panel in white as shown in the drawing so that the light section or light operated by each particular switch is indicated. A 10-ampere tumbler switch is used for the main circuit switch.

Board Will Be Approved by Inspectors.

In the above description only the essential points of construction have been touched upon since the drawings and the notes thereon describe the other points of construction fully.

The construction of this scoreboard is such that it should meet with the approval of all electrical inspectors. The whole device is electrically “dead” when the service plug is disconnected, which should always be done when not in use. Standard electrical parts are used and the construction is rather simple, so that any handy man can make an attractive and efficient device. In operation, the device is entirely fool-proof, being as positive of action as the turning on and off of a light in one’s home.

Remarkably Lifelike Little Dogs made from Pipe Cleaners

You have probably seen amusing little animal novelties made by twisting pipe cleaners together, hi most cases they are comical enough, but stiff and grotesque— almost childish. It is therefore a revelation to see, from the illustrations accompanying this article, what lifelike results can be obtained by one who is skillful at this pastime.—The Editor.

IN MAKING novelties from fuzzy pipe cleaners, it is perhaps best to start with a familiar animal like the dog. If you have a few cleaners and a pair of pointed nose pliers, you have everything necessary for your initial attempt. When you have completed a natural looking little dog, it can be used as an ornament on a radio cabinet, desk, or occasional table.

The size is optional, but small dogs are easier at the start. The length from nose to the end of the tail may be about 2 1/2 in. and the height 1 in.

Bend a cleaner to form one curved piece from the muzzle to the end of the tail. Let it be long at the nose end; you can cut the surplus off later when the length of the muzzle has been determined. You may leave the tail straight if you prefer it that way, or double it back to make it more stocky.

Now fasten the end of another cleaner securely at the base of the tail, and twist it tightly around the main part of the skeleton to form the body. Twist this tightly, putting one turn close against the other, and wind on another layer or two to build it to the right thickness.

The ears are formed from a single piece doubled in two places and fastened at the top of the forelegs. Wind another layer over this, starting at the front shoulders, to make the neck. Crisscross the turns between the ears to hold them in place. Then wind the muzzle, the length depending on the breed of dog you are modeling. It will be necessary to wind more than one layer on the neck and muzzle to build up the thickness.

Any short pieces left over will do to wind high up on the legs, close to the body. Then clip the legs off the correct length and bend to their natural form.

The eyes and nose may be indicated with ink spots, or small glass headed pins, cut off short and with a touch of glue on them, may be used for eyes. A slight twist to the head will give the completed dog a natural expression.

Practice and close observation are the secrets of success. —Wilbur F. Hull.

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A Home-Built Miniature Motorbike for Youngster

by THEODORE HODGDON

A youngster will get some keen thrills out of driving his own specially designed midget motorbike along the highways at a clip of 40 m.p.h. Read this article to learn how to build one of these miniature jobs or cut down a big machine to make it suitable for a 10-year-old boy.

AN EXCEPTIONAL opportunity for the mechanically-minded person to exercise his ingenuity and creative ability is afforded in the construction of miniature motorcycles for youngsters ranging all the way from three up to eight or ten years of age.

When complete, these tiny motorcycles operate exactly like their larger brothers, which may be seen in the hands of sportsmen and motorcycle policemen. The tiny engines propel the little machines along at 35 or 40 miles an hour, yet are easily controlled at a twist of the wrist by regular motorcycle throttle and spark grip.

Needless to say, the youngster who is in possession of one of these custom built motorbikes is the envy of all his friends, and his grownups may feel that they are performing an educational service for the youngster in teaching him so early in life to control powerful forces.

If desired, a regular three-speed gearbox may be fitted, so that the young rider may learn to shift gears, as well as control engine speed in learning to drive the machine. A system of electric lights, electric horn, and other accessories, are adaptable to these tiny machines by the use of bicycle parts.

Also if desired, where there is more than one child in a family a diminutive sidecar can be put together and fastened to the motorcycle in orthodox manner so that young brother may take little sister for a ride through driveways, and perhaps across neighboring fields.

There are really two methods of constructing miniature motorcycles. The first is to design the small machine from start to finish, using pneumatic tricycle or bicycle wheels up to 15 or 16″ in diameter, constructing the frame of steel tubing, flattened at the ends and bolted together, and using a small one cylinder outboard motor engine, or perhaps an old washing machine engine or even a lawnmower motor, provided it is small enough.

These very small machines will weigh only 35 or 40 lbs. when complete, and therefore not very much power is required to propel them along at a brisk clip. Three speed gears are not really necessary on so small a machine, but almost any motocycle dealer will have on hand a small three-speed gearbox which may have been taken from some ancient lightweight motorcycle.

Usually these gearboxes are not too heavy, and they may be neatly installed in the frame, as shown in the drawing on this page.

“Grown-up” Bike Cut Down to Midget Size The second method of building a miniature two-wheeler is that of taking the ordinary sized motorcycle and cutting it down to ten-year-old boy’s size as shown in accompanying illustrations. In performing such an operation on the large machine, it is best to start with a motorcycle that is not too large, such as a 37 cu. in. twin, or perhaps a 21 cu. in. single. The builder should then secure a large sheet of paper (brown manila wrapping paper will do). Pin it on the floor or wall, and lay out the new design for the frame, full or half scale, figuring on taking out sections here and there so that the engine when put back into the frame will clear the ground by only two or three inches, and the frame itself will hug the top of the engine very closely.

Sections Sawed Out of Bike Frame The shortening of many of the frame tubes is necessary, and this is easily accomplished by sawing out sections and putting them back together with reenforcements inserted as shown in the sketches.

The front forks and the rear fork tubes also must be shortened to accommodate the pair of small wheels, preferably airplane wheels, of about the size used on the tail skid of the great trimotor Ford airplane. These wheels complete with tires may be secured as small as 12″ in diameter, although it will be far more economical to use regular airplane wheels and tires, which may be purchased second-hand in sizes as small as 15 or 16″x-3-1/2″ or 4″ (tire size).

The mudguards must also be cut down and by careful heating and occasionally splitting with a hacksaw they may be bent to perform with the size of airplane wheels which you employ. A little ingenuity will solve the problem.

The installation of the front wheel offers no particular difficulty but the rear wheel, before it is installed in the fork, must be fitted with a sprocket on one side and a brake drum on the other. This may be accomplished by a simple brazing operation. It is not necessary to go into an expensive machining operation in fitting the brake and sprocket to the rear wheel, because of the light weight and slow speed which the small motorcycle will achieve.

The gasoline tank of a regular motorcycle may be cut down as shown in the sketches. The front portion of the tank is removed, and the rear portion forms a neat tank provided the front end is done well with pains and much careful shaping put into the job.

Handlebars also must be shortened and perhaps a bicycle seat installed in place of the large motorcycle seat.

Nearly all electrical equipment can be put back into the machine except perhaps the storage battery and generator, for which it is possible to substitute one or two dry cells in a bicycle lamp case.

When complete the entire motorcycle may be carefully enameled with a two-tone color combination such as may be seen on the late sport model motorcycles put out by the great motorcycle factories.

The construction of a tiny sidecar to fit a motorcycle of this type is a comparatively simple matter. The chassis is built up of tubing, either bolted or brazed together, depending upon the facilities available to the builder. A bolted chassis will do, provided no very high speeds are attempted with the tiny machine. The body itself is easily built up of a wooden frame, covered with sheet tin or aluminum and upholstered with padding and leather obtained from old automobile cushions.

This tiny body may be hung upon small buggy seat springs or coil springs, such as may be found in almost any automobile spare parts depot.

When ready for the road, the miniature motorcycle should start easily, either by pushing or by kick starter, and the carburetor control should be adjusted so that it will run at very slow speeds, in order that the youngster may become accustomed to it without fear of its power. In fact, it is advisable to set the adjusting stop screw on the top of the carburetor so that the throttle cannot be opened more than perhaps one-quarter or one-half of its full throttle, at least until the youngster becomes accustomed to the motorcycle.

If carefully planned and painstakingly constructed, one of these miniature motorcycles can be a source of great pride both to its young owner and the man whose handwork it represents.

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An Electric Miniature Mono-Railway

IT IS a well known fact among experimenters that when a whirling gyroscope is set in an upright or inclined position it will not change unless some strong exterior force is applied. Due to this peculiar quality, which is known as the precessive effect, the gyroscope can be utilized in the construction of many scientific instruments and practical devices which are used in every day life.

One of the most important uses to which the gyroscope is put is that of keeping a mono-rail train in an upright position as it speeds along on its single track. The most practical and outstanding railway of this kind is known as the Brennan Mono-railway, which is used in Ireland.

An interesting and instructive toy mono-railway working on the same principle as its big brother can be easily made by any home craftsman out of a few Meccano parts, an old six-volt toy motor, a bell transformer, a piece of No. 20 gauge sheet iron, an old sewing machine fly wheel, and some No. 14 bare copper wire.

The body of the train is made from the piece of sheet iron, which is cut to the dimensions given in Fig. 2, and nailed around the baseboard, as illustrated. A second piece of sheet iron can be cut to the required shape and soldered on the top of the cabin to serve as a roof.

From an old Meccano model builder set you can obtain the pulleys with which to make the trucks. Mount these wheels in the the two carriages cut from pieces of thick sheet iron bent into square cornered U’s. Two small round headed stove bolts are used as hubs. The completed carriage is fastened to the bottom of the baseboard with threaded pins, which are connected with one terminal of the motor to provide contact with the rail-wire.

The next step is to construct the gyroscope, which in this case is kept extremely simple. The gimbal is made from two strips of sheet brass cut in the shapes shown in Fig. 1. The strip at the base has a dent punched in the center to hold the lower point of the flywheel hub. The upper strip is a little more complicated, however. It has a long, narrow slit cut in it, with a l/16th-inch jog in the center.

The reason for this is plain on a little study. If the gyroscope is mounted on straight gimbals, there will he no turning or righting effect. But with the jog, or precession fork, the minute gravity attempts to sway the car the gyro hub hits the righting notch in the precession fork, bringing the car immediately into an upright position.

The flywheel from an old Model 10 Singer sewing machine will serve as a flywheel for the gyroscope. A small notch is filed in the hub to form the pulley, as shown in Fig. 1. As a driving belt, you can use four rubber bands.

The gyroscope is driven by a six-volt electric motor which is mounted on the base board in the position illustrated. The Meccano Model Builder set will supply you with parts for constructing the gear and pulley system which connects the motor to i the gyro. The gears should be so arranged that the gyro will turn at a rate of about 6000 revolutions per minute.

A trolley is all that is needed now to complete the car. This can be made of a piece of No. 10 bare copper wire bent into the shape shown in the drawing and soldered or bolted to the top of the sheet iron cabin. A wire is soldered to the supporting bolt and run to the remaining terminal of the motor.

With the train now completed, you can proceed to erect the trolley wire and the rail, both of which consist of lengths of No. 14 bare copper wire suspended in the manner shown in the accompanying drawings. Insulators are placed at both ends to avoid short circuits, and at the house end two leads are taken off and run to the secondary of a bell transformer, which supplies the current through the wires to the motor.

In running the car, you will have to allow several minutes for the flywheel of the gyroscope to pick up speed. This might take longer, as there will no doubt be a lot of slipping in the belt. When once it has worked up to a good speed, a gentle shove will send the train moving along the wire. To give a realistic effect to the car, you can paint it an aluminum color, and add a small headlight to the front. In- case no bell transformer is procurable, you can use a six-volt storage battery or four dry cells in series. A control board is arranged as shown.

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Model of Rome Took Thirty Years to Build

After more than thirty years of work, a French architect, Paul Bigot, has completed a stupendous task, the building of an accurate relief map of Rome as it was about the fourth century, A.D., when the city was at the peak of its power. At that time Rome was the center of as much of the world as was then known. It had gathered the riches of conquered countries and was crowded with temples, palaces, shrines and stadiums. Few of these have escaped destruction but most of the structures have left a trace, either in book or in stone, and M. Bigot carefully studied every source of Roman history before attempting to construct this ancient city as the Caesars knew it. The plaster model of the Eternal City is twenty feet wide and forty feet long and thousands of little blocks represent the monuments and buildings of the past. The scale is one to 400 and three-fourths of the city is represented. Every detail is carefully reproduced so that looking at the model gives the same impression, it is claimed, as though the observer had been able to fly over the Rome of ancient days and view the city from an airplane. The model has been placed for exhibition in the Paris institute of art and archaeology.

Builds Organ of 550 Pipes in a Garage

Using his garage as a workshop, and giving only his spare time to the task, H. T. Adams, of Ham, Surrey, England, built the 550-pipe organ shown in the photograph at the left. Although Adams, an automotive engineer, had had no previous training in the work, he constructed every part of the twelve-foot-high organ himself, except the metal pipes. The only plans which he employed were those to guide him in assembling the intricate mechanism of the console.

“Woolworth Cow” Eats Wire Grass

ALEXANDER CALDER, New York sculptor and artist, recently gave an exhibition of his work at the Fifty-sixth Street Galleries. Although many fine works of art were shown, the amusing toy novelties of this versatile craftsman attracted the largest share of attention.

Using scraps that may be picked up around any home and every day articles purchased from the five and ten cents stores, Calder constructed many startling novelties. The “Wool-worth Cow” shown here was made of a wooden darning egg, a door bumper, coat hangers, bottle tips, rubber tips and wire.

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How Auto Horns Work

What happens when you press the button? You’ll see quickly if you make these simple working models.

By Kenneth M. Swezey

THE makers of auto horns have come as far from their early baa-DOO-gah! days as have their brother engine designers. So if the horn on your new car both sounds better and carries farther, it’s no accident.

Some horn developments have been purely technical, but others have turned upon the physics of sound. Designers have found, for instance, that pitch is more important than loudness (amplitude) in achieving carrying power, and that loud sounds aren’t so unpleasant if they have a musical tone.

Next to fire-engine sirens, the most powerful horns today are the air-blown trumpets used on cross-country trucks and busses and as custom accessories for passenger cars. They work like trumpets in a band, with vibrating reeds or diaphragms taking the place of players’ lips.

Magnetically actuated, vibrating-diaphragm electric horns are standard on most passenger cars. They work like household buzzers. The vibrating part is connected by a rod to a thin metal diaphragm.

Horn makers also produce whistles that operate from the exhaust, and air and electric horns on which you can play tunes.

You can see how the various kinds of horns work by performing the experiments below and on the next two pages.

ELECTRIC HORN.

You can make a working model like the one above in a few minutes. Its magnet is a bolt wound with insulated copper wire. Mount this on an angle bracket.

The L-shaped armature is bent from a strip of tin. The diaphragm is a disk of stiff paper glued at the edge over a smaller hole cut in a piece of corrugated cardboard. Link the diaphragm and armature by a matchstick secured at each end with a drop of sealing wax. The current-breaking contact is formed by the bare tip of one end of the magnet wire that just touches the far side of the armature when the battery is off.

When you connect the free end of the magnet winding to one pole of your battery and the base of the armature to the other, current flows through the coil. The coil becomes magnetized and pulls the armature toward it. This breaks the circuit between armature and contact point, causing the armature to spring back again—only to be once more attracted. The sound of the vibrating armature is increased by the paper diaphragm attached to it. Tone and intensity can be adjusted slightly by changing the pressure on the contact wire. A cardboard cone held against the diaphragm will make the sound louder.

AIR HORN.

This variety produces a sound in much the same way that a tin horn or your vocal cords do. The old honk-honking horns depended upon a thin metal reed that vibrated strongly when you squeezed the bulb. Some present-day musical horns work on the same principle. More powerful air horns depend upon the vibration of a diaphragm against the end of a trumpet.

You can make a workable vibrating-reed horn from a soda straw. Flatten one end and cut about 1/4″ from each corner as shown in the diagram. Put about 2″ of this end into your mouth. Then blow. Shorten the straw and you will raise the pitch. Add funnels of different sizes and shapes over the end of the straw and you will change and magnify the sound just as trumpets do on a real horn.

KLAXON.

Horns of this famous type make their OOgah sound when a studded wheel rotates against a projection on the back of a diaphragm. The wheel is turned by an electric motor or by hand through a train of gears. Pitch is changed by varying the wheel speed. You can make a model by cementing a thumbtack to the center of the bottom of an empty salt box, and rubbing a file over the point.

WHISTLE.

Whistle-type horns work like an organ pipe. A blast of air passes over a sharp edge near one end of a metal pipe. The turbulent air at the edge starts the air in the pipe vibrating at its own natural frequency, determined by the length of the pipe. You can test this principle with soda straws and bottles, as below. Combination tones can be produced by blowing over several bottles of different sizes at once.

SIREN.

Now often restricted to fire engines, ambulances, police cars, and air-raid warnings, a siren produces its characteristic scream by intermittent puffs of air issuing through holes in a revolving drum or disk. A simple model will show how it works. Punch a circle of equally spaced holes near the edge of a coffee-can cover. Mount the cover on the shaft of a small grindstone or fasten it in the chuck of a hand drill. Blow through the holes with a straw, flattened at the nozzle end, as you turn the disk. The harder you blow, the louder; the faster you turn, the higher the pitch.

Commercial sirens usually consist of a metal drum with slots in the periphery. This revolves inside a slotted stationary drum. A fan attached to the rotating drum sucks in air at the axis and hurls it out the slots.

How sound waves are intensified by the use of a trumpet can be shown visually with a candle and a tin can. Remove the top from the can, hold the top a little more than the can’s length from the candle, and snap the top with your finger. The candle doesn’t flicker. Now hold the mouth of the empty can near the candle, and snap the bottom of it. This time the sound waves, aimed by the can, disturb the candle flame noticeably.