Page:Popular Science Monthly Volume 92.djvu/172

 Popular Scie7ice Monthly

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in Fig. 1. These serve as insulators.

In Fig. 3 is shown how the above de- scribed Tesla coil with a few alterations can be converted into an Oudin coil. The three small blocks A are used to support the secondary.

The hook-up for a Tesla coil is shown in Fig. 4, and the abbreviations used are as follows: R. S. G., rotary spark gap; C and C, condensers; S. G., safety gap.

Various experiments are shown in Figs. 5, 6 and 7. The two wires in Fig. 5 are connected with the binding posts of the secondary and are left to project verti- cally in the air. Long streamers wave about, producing a weird effect.

The experiment in Fig. 6 produces a cone of light. Two wire hoops, one 12 in. in diameter and the other 3 in. in diam- eter, are connected with the secondary, and the lead wires are so bent that the hoops are separated 5 or 6 in.

When a gap is made as shown in Fig. 7, a spark 10 to 12 in. is obtained. Of course all these experiments should be made in the dark.

If two metal disks about 1 in. in diam- eter are provided and one attached to each of the connection leads, a brilliant flow of light will be produced from their edges. For another experiment, suspend two metal rods from the ceiling or other support so that they will hang about 2 in. apart. Connect these to the leads. Sparks will start at the bottom and run to the top, making a ladder of light.

When the coil is converted into an Oudin coil the bottom binding post is connected with the lower turn of the primary; otherwise the connections are the same as for the Tesla coil, as shown in Fig. 4. A brass ball 2 in. in diameter. Fig. 8, should be screwed on the top binding post of the secondary in place of the thumbnut. One of these may be obtained from an iron bed.

An interesting field for high frequency experimenting is in connection with the X-rays. The bulb, Fig. P, is connected with the secondary leads of the Tesla coil at A and B on the bulb. The wire C is the vacuum regulator, and is oper- ated by bending it over near A so a, spark will jump while the tube is running. Good X-ray photographs of the hand or other objects may be made with this apparatus. To take an X-ray photo-

��graph, load a plate holder with one plate only, then expose it, holding your hand or other object against the side of the plate holder nearest the plate. The X-rays penetrate the light-proof slide with ease. The time of exposure can only be determined by trial. A good printing negative can be made by holding the plate holder 5 in. from a 6-in. tube and exposing it for 2 minutes.

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An Electric Torch Made of Bichro- mate Solution in a Bottle

ONE of the most novel of the many electric torches recently invented, consists merely of a wide-mouthed bottle having rods of zinc and carbon inserted through a rubber cork. These rods pro- ject down into the bottle for about one- third of its depth. On top of the cork a small electric lamp is mounted, similar to those used in ordinary electric torches. Connections are made between the lamp and the zinc and carbon rods.

A mixture of water, bichromate of potash, and sulphuric acid is put into the bottle, and stands at a level of about 1 in. below the end of the zinc and carbon rods when the bottle is upright. When the bottle is turned upside-down, it becomes what is known as a bichromate cell, a well-known type of cell for pro- ducing small quantities of electricity for electric bells and similar devices. The electric current produced when the solu- tion surrounds the zinc and carbon rods is strong enough to light up the lamp, and the apparatus becomes an electric torch. The cork of the bottle must, of course, be made perfectly water-tight.

Square bottles with large round mouths, such as are used for pickles and similar products, are very suitable for these torches, as they can be laid down on their sides when light is required.

��Lacing Belts Through Eyeleted Holes in the Leather

The life of a belt may be lengthened considerably, if instead of the customary slits in the belt, eyelets obtained from old shoes are substituted through which to pass the thong in lacing. These will prevent the thong from tearing out under the strain when drawn tight.

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