Page:Popular Science Monthly Volume 89.djvu/152

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An easily constructed anchor-gap which

may also be used as a plain gap for an

ordinary spark-coil

A Simple Anchor -Gap

THE .drawing shows a simple and easily' constructed anchor-gap. All that is required is a porcelain cleat, about I in. by 2 ins. of i/i6in. sheet brass and two common battery bolts. The holes are afterward sealed with some insulating compound. The slot in one plate facilitates fine adjustment, and this gap may be used to advantage as a plain gap for a small spark-coil, as well as for an anchor-gap. — G. Dunfee.

Making a Mechanical Interrupter

MANY experimenters have trouble with the vibrators on coils, since \'ery few work satisfactorily. A mechan- ical vibrator, run by a small motor may roof.leee/ ^

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��Side view of interrupter

���View from above. The vibrator can be

made from odd pieces of metal which

happen to be at hand

��be constructed according to the drawing and will be found to eliminate many of the difficulties. The faster the motor runs, the higher the frequency of interruption.

This vibrator can be constructed from odds and ends, as shown. The toothed wheel should be made of brass, and the teeth cut in with a hacksaw. The vibrative arm is also brass. Soldered to it is a piece of spring steel in which a piece of platinum for one contact is fastened. Two uprights hold the adjust- ing-screw. The rest of the construction can be seen from the illustration; dimensions are not given, since they may be chosen almost at the will of the experimenter. — H. B. Pearson.

Temporary Variable Condenser

TH ERP2 have been described numerous makeshift variable condensers; but the one here shown is about the simplest, and can be made in a few minutes.

A bottle of thin glass is filled with some good conduc- tive liquid such as mercury. If enough quicksiher cannot be had, salt and water or a so- lution of sal-am- moniac will an- swer. An insu- lated wire with the end bared is thrust deep into the liquid and clamped with the cork; this rep- resents one plate of

the condenser. The other plate is a tin can or other vessel partly filled with the same conductive liquid and having a wire clamped on the edge. The bottle is suspended by passing the wire through a hole in a small [)iece of wood, and plugging it at the height required. Care must be taken that the liquid in the can does not reach the wire extendidg from the bottle.

Of course with mercury in both and with the outer receptacle made of glass, the best results will be secured. This simple arrangement can be made in a short time, and will be found practical for maiu' simple ex|)eriments.

���A simple form of variable condenser

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