The Boy Mechanic Part 70

the winter time when the regular game cannot be played outdoors.

The knife is opened and loosely stuck into a board, as in Fig. 1, and with a quick upward movement of the forefinger it is thrown into the air to fall and land in one of the positions shown. The plays are determined by the position of the knife after the fall.

A foul ball is indicated by Fig. 2, the knife resting on its back.

The small blade sticking in the board which holds the handle in an upright position, as shown in Fig. 3, calls for a home run. Both blades sticking in the board (Fig. 4), a three-base hit. A two-base hit is made when the large blade sticks in the board, Fig. 5. A one-base hit is secured when the large blade and the end of the handle touch the board as in Fig. 6. The knife falling on its side (Fig. 7) calls for one out. Each person plays until three outs have been made, then the other plays, and so on for nine innings.

--Contributed by Herbert Hahn, Chicago.

** How to Remove Paper Stuck to a Negative [250]

When making photographic prints from a negative, sometimes a drop of moisture will cause the print to stick to the gelatine film on the gla.s.s. Remove as much of the paper as can be readily torn off and soak the negative in a fresh hypo bath of 3 or 4 oz. hypo to 1 pt. of water for an hour or two. Then a little gentle rubbing with the finger-not the finger nail will remove anything adhering to the film. It may be found that the negative is not colored. If it is spotted at all, the negative must be washed for a few minutes and placed in a combined toning and fixing bath, which will remove the spots in a couple of hours. The negative must be well washed after going through the solutions to take away any trace of hypo.

** Old-Time Magic - A Sack Trick [251]

The magician appears accompanied by his a.s.sistant. He has a sack similar to a meal bag only on a large scale. The upper end of this bag is shown in Fig. 1, with the rope laced in the cloth. He then selects several people from the audience as a committee to examine the sack to see that there is absolutely no deception whatever in its makeup. When they are satisfied that the bag or sack is all right, the magician places his a.s.sistant inside and drawing the bag around him he allows the committee to tie him up with as many knots as they choose to make, as shown in Fig. 2.

The bag with its occupant is placed in a small cabinet which the committee surround to see that there is no outside help. The magician then takes his watch and shows the audience that in less than 30 seconds his a.s.sistant will emerge from the cabinet with the sack in his hand. This he does, the sack is again examined and found to be the same as when it was first seen.

[Ill.u.s.tration: Sack Trick-Holding the Rope Inside the Bag]

The solution is when the a.s.sistant enters the bag he pulls in about 15 in. of the rope and holds it, as shown in Fig. 3, while the committee is tying him up. As soon as he is in the cabinet he merely lets out the slack thus making enough room for his body to pa.s.s through. When he is out of the bag he quickly unties the knots and then steps from his cabinet.

--Contributed by J. F. Campbell, Somerville, Ma.s.s.

** The Invisible Light [251]

The magician places two common wax candles on a table, one of them burning brightly, the other without a light. Members of the audience are allowed to inspect both the table and the candles.

The magician walks over to the burning candle, shades the light for a few seconds, turns to the audience with his hands a few inches apart, showing that there is nothing between them, at the same time saying that he has a light between his hands, invisible to them (the audience), with which he is going to light the other candle. He then walks over to the other candle, and, in plain sight of the audience lights the candle apparently with nothing.

In reality the magician has a very fine wire in his hand which he is heating while he bends over the lighted candle, and the audience gaze on and see nothing. He turns to the other candle and touches a grain of phosphorus that has been previously concealed in the wick with the heated wire, thus causing it to light.

--Contributed by C. Brown, New York City.

** Using the Sun's Light in a Magic Lantern [251]

The light furnished with a small magic lantern does very well for evening exhibitions, but the lantern can be used in the daytime with good results by directing sunlight through the lens instead of using the oil lamp. A window facing the sun is selected and the shade is drawn almost down, the remaining s.p.a.ce being covered by a piece of heavy paper. A small hole is

[Ill.u.s.tration: Magic Lantern]

cut in the paper and the lantern placed on a table in front of the hole, the lamp having been removed and the back opened. The lantern must be arranged so that the lens will be on a horizontal line with the hole in the paper. A mirror is then placed just outside of the window and at such an angle that the beam of light is thrown through the hole in the paper and the lens of the lantern.

The shades of the remaining windows are then drawn and the lantern is operated in the usual way.

--Contributed by L. B. Evans, Lebanon, Ky.

** A Handy Drill Gauge [252]

The accompanying sketch shows a simple drill gauge which will be found very handy for amateurs. The gauge consists of a piece of hard wood, 3/4 in. thick, with a width and length that will be suitable for the size and number of drills you have on hand. Drill a hole through the wood with each drill you have and place a screw eye in one end to be used as a hanger. When you want to drill a hole for a pipe, bolt,

[Ill.u.s.tration: Drill Gauge]

screw, etc., you take the gauge and find what size drill must be used in drilling the hole.-Contributed by Andrew G. Thome, Louisville, Ky.

** Stove Polish [252]

A good stove polish can be made by mixing together 1 lb. of plumbago, 4 oz. of turpentine, 4 oz. of water and 1 oz. of sugar.

Mix well and apply with a cloth or brush.

A Home-Made Daniell Cell [252]

An effective Daniell galvanic cell may be constructed from material costing very little money. A common tin tomato can with a copper wire soldered to the top forms the jar and positive electrode. A piece of discarded stove zinc rolled into an open cylinder of about 1-1/2-in. diameter, 5 in. long, with a copper wire soldered at one end forms the negative electrode.

To make the porous cell, roll a piece of heavy brown wrapping paper, or blotting paper, into a tube of several thicknesses, about 5 in. long with an internal diameter of 2 in. Tie the paper firmly to prevent unrolling and close up one end with plaster of paris 1/2 in. thick. It is well to slightly choke the tube to better retain the plaster. The paper used must be unsized so that the solution scan mingle through the pores.

Two liquids are necessary for the cell. Make a strong solution in a gla.s.s or wooden vessel of blue vitriol in water. Dilute some oil of vitriol (sulphuric acid) with about 12 times its measure of water and keep in a bottle when not in use. In making up the solution, add the acid to the water with constant stirring. Do not add water to the acid.

The cell is charged by placing the zinc in the paper tube and both placed into the tin can. Connect the two wires and pour the dilute acid into the porous cell around the zinc, and then immediately turn the blue vitriol solution into the can outside the paper cup.

A current generates at once and metallic copper begins to deposit on the inside of the can. It is best to let the action continue for a half hour or so before putting the cell into use.

[Ill.u.s.tration: Daniell Cell]

Several hours working will be required before the film of copper becomes sufficiently thick to protect the tin from corrosion when the cell stands idle. For this reason it will be necessary to pour out the blue vitriol solution into another receptacle immediately after through using, as otherwise the tin would be soon eaten full of holes. The porous cup should always be emptied after using to prevent the diffusion of the blue vitriol solution into the cup, and the paper tube must be well rinsed before putting away to dry.

This makes one of the most satisfactory battery cells on account of the constancy of its current, running for hours at a time without materially losing strength, and the low cost of maintenance makes it especially adapted for amateurs' use. Its current strength is about one volt, but can be made up into any required voltage in series. A battery of a dozen cells should cost not to exceed 50 cts. for the material, which will give a strong, steady current, amply sufficient for all ordinary experimental work.

A strong solution of common salt may be used in place of the oil of vitriol in the porous cup, but is not so good.

--Contributed by C. H. Denniston, Pulteney. N. Y.

** A Home-Made Equatorial [253]

By Harry Clark

The ordinary equatorial is designed and built for the lat.i.tude of the observatory where it is to be used. This is necessary since the hour axis must point to the north pole of the heavens whose elevation above the horizon is equal to the lat.i.tude of the observer's station. The final adjustment of an ordinary equatorial is very tedious so that when once set up it is not to be moved.

This calls for a suitable house to protect the instrument. It has been the aim of the writer to build a very simple instrument for amateur work which would be adjustable to any lat.i.tude, so easily set up ready for work and so portable that it need not be left out of doors from one evening until the next.

[Ill.u.s.tration: Instrument for Locating Stars]

The instrument is mounted on a tripod or piece of iron pipe carrying a short vertical rod of 3/8-in. steel. A rectangular wooden frame with suitable bearings rotates about this shaft. The frame has also two horizontal bearings carrying a short shaft to the end of which the frame carrying the hour axis is firmly clamped. By this arrangement of two perpendicular shafts the hour axis may be directed to any point in the heavens without care as to how the tripod or pipe is set up.