The Boy Mechanic Part 50

[Ill.u.s.tration: Disappearing Coin]

** Sticking a Coin Against the Wall [176]

Cut a small notch in a coin--ten cent piece or quarter will do--so a small point will project. When this is pressed firmly against a wood casing or part.i.tion the coin will stick tightly.

** A Chinese Outdoor Game [176]

The accompanying ill.u.s.tration shows the "grand whirl," or the Chinese students' favorite game. This game is played by five persons, four of them turning around the fifth or central figure

[Ill.u.s.tration: Chinese Doing the Grand Whirl]

with their arms locked about each other and the two outside persons swinging in midair with their bodies almost horizontal.

** Home-Made Photograph of a Lightning Flash [176]

How many times has each amateur photographer tried to photograph the lightning's flash? Some good pictures have been obtained by a ceaseless effort on the part of the operator. Here is a method by which you can make a picture of a streak of lightning on a clear night in your own house. Paste two strips of black paper on a piece of gla.s.s that is 10 in. square so as to leave a clear s.p.a.ce through the center 2-in. or more in width. Smoke this uncovered s.p.a.ce over a candle's flame until the soot is thick enough to prevent light pa.s.sing through. Take a sharp lead pencil and outline a flash of lightning upon the smoked surface, using a fine needle to make the smaller lines, and then set the gla.s.s up against the back of two boxes which are set to have a s.p.a.ce between them of 4 or 5 in.

A lighted candle is held behind the gla.s.s so the light will s.h.i.+ne through for focusing the camera. After darkening the room set your camera ready for the exposure and burn a small quant.i.ty of flash light powder in the same place in which the candle was held. This will make an impression upon the plate of the flash drawn on the smoked gla.s.s.

[Ill.u.s.tration: Lightning Flash]

** How to Make a Static Machine [177]

Static electricity is produced by revolving gla.s.s plates upon which a number of sectors are cemented; these sectors, pa.s.sing through neutralizing brushes, distribute electric charges

[Ill.u.s.tration: Details of a Homemade Static Machine]

to collecting combs attached to discharging rods. The gla.s.s selected for the plates must be clear white gla.s.s, free from wrinkles, and of a uniform thickness. Two plates are necessary to make this machine, and the gla.s.s should be of sufficient size to cut a circular plate 16-in. in diameter. A hole must be made exactly in the center of each plate, and this should be done before cutting the circle. One of the best ways to make the hole is to drill the gla.s.s with a very hard-tempered drill, the cutting edge of which should be kept moistened with 2 parts turpentine and 1 part sweet oil while drilling. The hole is to be made 3/4 in. in diameter. The circle is then marked on each plate and cut with a gla.s.s cutter. The plates are trued up, after they are mounted, by holding a piece of emery wheel to the edges while they are turning. Water should be applied to the edges while doing the work.

The sectors are cut from tinfoil, 1-1/2 in. wide at one end, 3/4 in. at the other, and 4 in. long. A thin coat of sh.e.l.lac varnish is applied to both sides of the plates, and 16 sectors put on one side of each plate, as shown in Fig. 1. The divisions can be marked on the opposite side of the plate and a circle drawn as a guide to place the sectors at proper intervals.

The sectors should lie flat on the gla.s.s with all parts smoothed out so that they will not be torn from their places as the plates revolve. The sh.e.l.lac should be tacky when the pieces of tinfoil are put in place.

The collectors are made, as shown in Fig. 2, from about 1/4-in.

copper wire with two bra.s.s b.a.l.l.s soldered to the ends. The fork part is 6 in. long and the shank 4 in. Holes are drilled on the inside of the forks, and pins inserted and soldered. These pins, or teeth, should be long enough to be very close to the sectors and yet not scratch them when the plates are turning.

The frame of the machine is made from any kind of finished wood with dimensions shown in Fig. 3, the side pieces being 24 in. long and the standards 3 in. wide. The two pieces, C C, Fig. 3, are made from solid, close grained wood turned in the shape shown, with the face that rests against the plate 4 in. in diameter, and the outer end 1-1/2 in. in diameter, the smaller end being turned with a groove for a round belt. Before turning the pieces a hole is bored through each piece for the center, and this hole must be of such a size as to take a bra.s.s tube that has an internal diameter of 3/4 in. The turned pieces are glued to the gla.s.s plates over the center holes and on the same side on which the sectors are fastened. Several hours' time will be required for the glue to set. A fiber washer is then put between the plates and a bra.s.s tube axle placed through the hole. The plates, turned wood pieces, and bra.s.s axle turn on a stationary axle, D.

The drive wheels, EE, are made from 7/8-in. material 7 in. in diameter, and are fastened on a round axle cut from a broom handle. This wood axle is centrally bored to admit a metal rod tightly, and extends through the standards with a crank attached to one end.

Two solid gla.s.s rods, GG, Fig. 4, 1 in. in diameter and 15 in.

long, are fitted in holes bored into the end pieces of the frame.

Two pieces of 1-in. bra.s.s tubing and the discharging rods, RR, are soldered into two hollow bra.s.s b.a.l.l.s 2 or 2-1/2 in. in diameter.

The shanks of the collectors are fitted in these bra.s.s b.a.l.l.s with the ends extending, to which insulating handles are attached.

Bra.s.s b.a.l.l.s are soldered to the upper ends of the discharging rods, one having a 2-in. ball and the other one 3/4 in. in diameter.

Caps made from bra.s.s are fitted tightly on the ends of the stationary shaft, D, and drilled through their diameter to admit heavy copper rods, KK, which are bent as shown. Tinsel or fine wire such as contained in flexible electric wire are soldered to the ends of these rods, and the brushes thus made must be adjusted so they will just touch the plates. The caps are fitted with screws for adjusting the brushes. These rods and brushes are called the neutralizers. A little experimenting will enable one to properly locate the position of the neutralizers for best results.

--Contributed by C. Lloyd Enos, Colorado City, Colo.

** A Concrete Swimming Pool [178]

[Ill.u.s.tration: Home-Made Swimming Pool]

Several boys from a neighborhood in the suburbs of a large city concluded to make for themselves a swimming tank of concrete. The money was raised by various means to purchase the cement, and the work was done by themselves. The ground was selected in a secluded spot in a neighbor's back yard and a hole dug to a depth of 4 ft., 12 ft. wide and 22 ft. long. The concrete was made by mixing 1 part cement, 4 parts sand and 10 parts gravel together and the bulk moistened with water. The bottom was made the same as laying a sidewalk, and forms were only used for the inside of the surrounding wall. The tank may be hidden with shrubbery or vines planted to grow over a poultry wire fence.

** Old-Time Magic-Part IV [179]

Cutting a Thread Inside of a Gla.s.s Bottle [179]

This is a trick which can only be performed when the sun s.h.i.+nes, but it

[Ill.u.s.tration: The Gla.s.s Directs the Sun's Rays]

is a good one. Procure a clear gla.s.s bottle and stick a pin in the lower end of the cork. Attach a thread to the pin and tie a small weight to the end of the thread so it will hang inside the bottle when the cork is in place. Inform your audience that you will sever the thread and cause the weight to drop without removing the cork.

All that is required to perform the feat is to hold a magnifying gla.s.s so as to direct the sun's rays on the thread. The thread will quickly burn and the weight fall.

** Removing a Key from a Double String [179]

Tie the ends of a 5-ft. string together, making a double line on which a key is placed and the string held as shown by the dotted lines in the sketch. Turn the palms of the hands toward you and reach over with the little finger of the right hand and take hold of the inside line near the left-hand thumb.

[Ill.u.s.tration: "The Key Will Drop from the String"]

Reverse the operation and take hold of the inside line near right-hand thumb with the little finger of the left hand. You will then have the string as it appears in the sketch. Quickly let loose of the string with a little finger on one hand and a thumb on the other and pull the string taut. The key will drop from the string.

** How to Bore a Square Hole [179]

You would not consider it possible to bore a square hole in a piece of cardboard, yet such a thing can be done. Take a cardboard or a thin piece of wood, fold and place it between two pieces of board with the fold up; the boards are then put in a vise as shown. Start the bit with the screw point in the fold, using a 1-in. bit, and bore a

[Ill.u.s.tration: Boring a Square Hole]

hole 1/2 in. deep. When the cardboard is taken from the vise it will appear as shown at B and when unfolded, as at A.