The Boy Mechanic Part 120

[Ill.u.s.tration: Making a Microscope]

** A Novel Electric Time Alarm [433]

All time alarms run by clockwork must be wound and set each time.

The accompanying diagram shows how to make the connection that will ring a bell by electric current at the time set without winding the alarm. The bell is removed from an ordinary alarm

[Ill.u.s.tration: Electric Time Alarm]

clock and a small metal strip attached, as shown at B. An insulated connection is fastened on the clapper of the bell, as shown at A. The arm holding the clapper must be bent to have the point A remain as close to the strip B as possible without touching it. The connection to the battery is made as shown. When the time set for the alarm comes the clapper will be moved far enough to make the contact. In the course of a minute the catch on the clapper arm will be released and the clapper will return to its former place.

** How to Make a Phonograph Record Cabinet [433]

The core, Fig. 1, consists of six strips of wood beveled so as to form six equal sides. The strips are 3 ft.

[Ill.u.s.tration: Phonograph Wax Record Case]

long and 3 in. wide on the outside bevel and are nailed to three blocks made hexagon, as shown in Fig. 2, from 7/8-in. material.

One block is placed at each end and one in the middle. A 1/2-in.

metal pin is driven in a hole bored in the center of each end block. The bottoms of the pasteboard cases, used to hold the wax records, are either tacked or glued to this hexagon core, as shown in Fig. 3, with their open ends outward.

Two circular pieces are made of such a diameter as will cover the width of the core and the cases attached, and extend about 1/2 in.

each side. A 1/2-in. hole is bored in the center of these pieces to receive the pins placed in the ends of the core, Fig. 1. These will form the ends of the cabinet, and when placed, one on each end of the core, heavy building paper or sheet metal is tacked around them for a covering, as shown in Fig. 4. A small gla.s.s door is made, a little wider than one row of cases, and fitted in one side of the covering. The outside may be painted or decorated in any way to suit the builder.

** Experiments with a Mirror [434]

Ask your friend if he can decipher the sign as ill.u.s.trated in the sketch, Fig. 1, which you pretend to have read over the shop of an Armenian shoemaker.

He will probably tell you that he is not conversant with Oriental languages. He will not believe it if you tell him it is written in good English, but place a frameless mirror perpendicularly on the mysterious script, right across the quotation marks, and it will appear as shown in Fig. 2. We understand at once that the reflected image is the faithful copy of the written half.

With the aid of a few books arrange the mirror and the paper as shown in Fig. 3 and ask your friend to write anything he chooses, with the condition that he shall see his hand and read the script in the mirror only. The writer will probably go no farther than the first letter. His hand seems to be struck with paralysis and unable to write anything but zigzags, says Scientific American.

Another experiment may be made by taking an egg sh.e.l.l and tr.i.m.m.i.n.g it with the scissors so as to reduce it to a half sh.e.l.l. In the hollow bottom roughly draw with your pencil a cross with pointed ends. Bore a hole, about the size or a pea, in the center of the cross. Place yourself so as to face a window, the light falling upon your face, not upon the mirror which you hold in one hand.

Close one eye. Place the sh.e.l.l between the other eye and the mirror, at a distance of 2 or 3 in. from either, the concavity facing the mirror as shown in Fig. 4. Through the hole in the sh.e.l.l look at the mirror as if it were some distant object. While you are so doing the concave sh.e.l.l will suddenly a.s.sume a strongly convex appearance. To destroy the illusion it becomes necessary either to open both eyes or to withdraw the sh.e.l.l away from the mirror. The nearer the sh.e.l.l to the mirror and the farther the eye from the sh.e.l.l the more readily comes the illusion.

[Ill.u.s.tration: Experimenting with a Mirror]

** Miniature Electric Lamps [434]

After several years' research there has been produced a miniature electric bulb that is a great improvement and a decided departure from the old kind which used a carbon filament. A metallic filament prepared by a secret chemical process and suspended in the bulb in an S-shape is used instead of the old straight span.

The voltage is gauged by the length of the span. The brilliancy of the filament excels anything of its length in any voltage.

Of course, the filament is not made of the precious metal, radium; that simply being the trade name. However, the filament is composed of certain metals from which radium is extracted.

[Ill.u.s.tration: Types of "Radium" Lamps]

The advantages of the new bulb are manifold. It gives five times the light on the same voltage and uses one-half of the current consumed by the old carbon filament. One of the disadvantages of the old style bulb was the gla.s.s tip which made a shadow. This has been obviated in the radium bulb by blowing the tip on the side, as shown in the sketch, so as to produce no shadow.

** How to Make a Magazine Clamp [435]

This device as shown in the ill.u.s.tration can be used to hold newspapers and magazines while reading. Two pieces of wood are cut as shown, one with a slot to fit over the back of a magazine and the other notched to serve as a clamp. The piece, A, may be slotted wide enough to insert two or three magazines and made long enough to hold several newspapers.

[Ill.u.s.tration: Clamp]

** Pewter Finish for Bra.s.s [435]

A color resembling pewter may be given to bra.s.s by boiling the castings in a cream of tartar solution containing a small amount of chloride of tin.

** Drowning a Dog's Bark with Water [435]

The owner of two dogs was very much annoyed by the dogs barking at night. It began to be such a nuisance that the throwing of old shoes and empty bottles did not stop the noise. The only thing that seemed to put a stop to it was water.

[Ill.u.s.tration: Water Treatment for Dog's Bark]

Being on the third floor of the house, and a little too far from the kennel to throw the water effectively, a mechanism was arranged as shown in the sketch.

A faucet for the garden hose was directly below the window. An 8-in. wooden grooved pulley was slipped over an axle which had one end fitted on the handle of the faucet. A rope was extended to the window on the third floor and pa.s.sed around the pulley several times, thence over an iron pulley fastened to the wall of the house and a weight was attached to its end. By pulling the rope up at the window the large pulley would turn on the water and when released the weight would shut off the flow. The nozzle was fastened so as to direct the stream where it would do the most good.

--Contributed by A. S. Pennoyer, Berkeley, Cal.

** Cost of Water [435]

The average cost of supplying 1,000,000 gal. of water, based on the report of twenty-two cities, is $92. This sum includes operating expenses and interest on bonds.

** How to Make a Wondergraph [436]

By F. E. TUCK

An exceedingly interesting machine is the so-called wondergraph.

It is easy and cheap to make and will furnish both entertainment and instruction for young and old. It is a drawing machine, and the variety of designs it will produce, all symmetrical and ornamental and some wonderfully complicated, is almost without limit. Fig. 1 represents diagrammatically the machine shown in the sketch. This is the easiest to make and gives fully as great a variety of results as any other.

To a piece of wide board or a discarded box bottom, three grooved circular disks are fastened with screws so as to revolve freely about the centers. They may be sawed from pieces of thin board or, better still, three of the plaques so generally used in burnt-.

wood work may be bought for about 15 cents. Use the largest one for the revolving table T. G is the guide wheel and D the driver with attached handle. Secure a piece of a 36-in. ruler, which can be obtained from any furniture dealer, and nail a small block, about 1 in. thick, to one end and drill a hole through both the ruler and the block, and pivot them by means of a wooden peg to the face of the guide wheel. A fountain pen, or pencil, is placed at P and held securely by rubber bands in