The Boy Mechanic Part 22

The piston is made of a stove bolt, E, Fig. 2, with two washers, FF, and a cylindrical piece of hard wood, G. This is wound with soft string, as shown in Fig. 3, and saturated with thick oil. A slot is cut in the end of the bolt E, to receive the connecting rod H. The valve B is made of an old bicycle spoke, C, with the nut cut in half and filed down as shown, the s.p.a.ce between the two halves being filled with string and oiled.

The valve crank S, Fig. 1, is cut out of tin, or galvanized iron, and is moved by a small crank on the shaft. This crank should be at right angles to the main crank.

[Ill.u.s.tration: Engine in Operation]

The boiler, Fig. 4, can be an old oil can, powder can, or a syrup can with a tube soldered to it, and is connected to the engine by a piece of rubber tubing. The heat from a small gas stove will furnish steam fast enough to run the engine at high speed. This engine was built by W. G. Schuh and A. J. Eustice, of Cuba, Wis.

** Writing with Electricity [74]

Soak a piece of white paper in a solution of pota.s.sium iodide and water for about a minute and then lay it on a piece of sheet metal. Connect the sheet metal with the negative or zinc side of a battery and then, using the positive wire as a pen, write your name or other inscription on the wet paper.

[Ill.u.s.tration: Electrolytic Writing]

The result will be brown lines on a white background.

--Contributed by Geo. W. Fry, San Jose, Cal.

** To Photograph a Man in a Bottle [74]

Neither a huge bottle nor a dwarfed man is necessary for this process, as it is merely a trick of photography, and a very amusing trick, at that.

First, photograph the person to be enclosed in the bottle against a dark plain background and mark the exact position on the ground gla.s.s. Let the exposure be just long enough to show the figure distinctly. Then place an empty bottle against a dark background and focus so as to have the outlines of the bottle enclose those of the man. Let this exposure be about twice the length of the first, and the desired result is obtained.

** A Musical Windmill [74]

Make two wheels out of tin. They may be of any size, but wheel A must be larger than wheel B. On wheel A fasten two pieces of wood, C, to cross in the center, and place a bell on the four ends, as shown. The smaller wheel, B, must be separated from the other with a round piece of wood or an old spool. Tie four b.u.t.tons with split rings to the smaller wheel, B. The blades on the wheels should be bent opposite on one wheel from the others so as to make the wheels turn in different directions. When turning, the b.u.t.tons will strike the bells and make them ring constantly.

[Ill.u.s.tration: Musical Windmill]

** Optical Illusions [74]

By giving the page a revolving or rinsing motion the three circular figures printed on the next page appear to rotate. The best effect will be produced by laying the book down flat on the desk or table and revolving, first

[Ill.u.s.tration: Move These Figures Rapidly with a Rinsing Motion]

in one direction and then in the opposite direction, in such a way that any given point on the page will describe a circle of about 1/2 in. diameter. Fig. 1 then appears to rotate in the same direction as the revolution; Fig. 2 appears to revolve in the opposite direction, and Fig. 3 appears to revolve sometimes in the same direction and at other times in the opposite direction.

A curious effect can be produced with Fig. 1 by covering up Figs.

2 and 3 with a piece of plain paper and laying a coin or other small object on the paper. If the vision is then concentrated on the coin or other object while same is being revolved, Fig. 1 will be seen to rotate.

** Barrel-Stave Hammock [75]

A hammock made of barrel staves is more comfortable than one would think, considering the nature of the material employed in making it. Good smooth staves should be selected for this purpose, and if one cares to go to little trouble a thorough sandpapering will make a great improvement. Cut half circles out of each stave, as shown at AA, and pa.s.s ropes around

[Ill.u.s.tration: Cheap and Comfortable]

the ends as shown at B. When finished the weight will then be supported by four ropes at each end, which allows the use of small sized ropes, such as clothes lines. A hammock of this kind may be left out in the rain without injury.

--Contributed by H.G.M., St. Louis, Mo.

** A Singing Telephone [75]

Those who have not already tried the experiment may be interested to know that a telephone may be made to sing by holding the receiver about 1/16 in. from the transmitter, as shown in the ill.u.s.tration. The experiment will

[Ill.u.s.tration: To Make a Telephone Sing]

work well on most telephones, but not on all.

When the receiver is placed in the position shown it acts like an ordinary buzzer, and the function of the transmitter will then be that of an interrupter. The slightest movement of the transmitter diaphragm will cause an increased movement of the receiver diaphragm. This in turn will act on the transmitter, thus setting up sympathetic vibrations between the two, which accounts for the sound.

** A Microscope Without a Lens [76]

By E. W. DAVIS

Nearly everyone has heard of the pin-hole camera, but the fact that the same principle can be used to make a microscope, having a magnifying power of 8 diameters (64 times) will perhaps be new to some readers. To make this lensless microscope, procure a wooden spool, A (a short spool, say 1/2 or 3/4 in. long, produces a higher magnifying power), and enlarge the bore a little at one end. Then blacken the inside with india ink and allow to dry. From a piece of thin

[Ill.u.s.tration: Detail of Lensless Microscope]

transparent celluloid or mica, cut out a small disk, B, and fasten to the end having the enlarged bore, by means of brads. On the other end glue a piece of thin black cardboard, C, and at the center, D, make a small hole with the point of a fine needle. It is very important that the hole D should be very small, otherwise the image will be blurred.

To use this microscope, place a small object on the transparent disk, which may be moistened to make the object adhere, and look through the hole D. It is necessary to have a strong light to get good results and, as in all microscopes of any power, the object should be of a transparent nature.

The principle on which this instrument works is ill.u.s.trated in Fig. 2. The apparent diameter of an object is inversely proportional to its distance from the eye, i. e., if the distance is reduced to one-half, the diameter will appear twice as large; if the distance is reduced to one-third, the diameter will appear three times as large, and so on. As the nearest distance at which the average person can see an object clearly is about 6 in., it follows that the diameter of an object 3/4 in. from the eye would appear 8 times the normal size. The object would then be magnified 8 diameters, or 64 times. (The area would appear 64 times as large.) But an object 3/4-in. from the eye appears so blurred that none of the details are discernible, and it is for this reason that the pin-hole is employed.

Viewed through this microscope, a fly's wing appears as large as a person's hand, held at arm's length, and has the general appearance shown in Fig. 3. The mother of vinegar examined in the same way is seen to be swarming with a ma.s.s of wriggling little worms, and may possibly cause the observer to abstain from all salads forever after. An innocent-looking drop of water, in which hay has been soaking for several days, reveals hundreds of little infusoria, darting across the field in every direction. These and hundreds of other interesting objects may be observed in this little instrument, which costs little or nothing to make.

** How to Make a Telegraph Key and Sounder [76]

The sounder, Fig. 1, is made from an old electric-bell magnet, D, fastened to a wooden base. The lever, A, can be made of bra.s.s and the armature, C, is made of iron. The pivot, E, is made from a wire nail and is soldered to A. It should be filed to a point at each end so as to move freely in the bearings, B, which are pieces of hard wood. The spring, H, is fastened at each end by pins, bent as shown, and should not be too strong or the magnet will be unable to move the armature.

[Ill.u.s.tration: SOUNDER-A. bra.s.s: B. wood: C. soft iron; DD. coils wound with No. 26 wire: E. nail soldered on A; FF. binding posts: H spring]

The stop, K, is a wire nail driven deep enough in the base to leave about 1/8 in. between the armature and the magnet. The binding posts, F, may be taken from old dry batteries and are connected to the two wires from the magnet by wires run in grooves cut in the base.

The base of the key, Fig. 2, is also made of wood and has two wooden bearings, E, which are made to receive a pivot, similar to the one used in the sounder. The lever of the key is made of bra.s.s and has a hardwood k.n.o.b, A, fastened near the end. A switch, D, connects with the pivot at F and can be either made from sheet bra.s.s, or taken from a small one-point switch. The binding posts are like those of the sounder, and are connected to the contacts, K, by wires run in grooves cut in the wood.