Page:Popular Science Monthly Volume 89.djvu/773

 Popular Science Muiif/ili/

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��sistanct's are shown in the separate circuits for the purpose of reguiatiiiii the currciU.

If the mechanisms to be controlled do not require so much power a low \oltage battery circuit may be used instead of the lighting circuit. The resistance of the Hashlight wire should be low enough to permit of its heating to a red hot temperature when the current is switched on. To pre\ent this wire fr(jm acting as a short circuit on the (Jther apparatus it should be small enough in size to actually fuse and break its circuit; ordinary fuse wire is not very suitable for this purpose, but fine strands of copper wire may be used in the absence of resistance wire. The charge of Hash- light powder should explode within the one second during which the camera- shutter is open.

All of this apparatus maj' be installed in some hidden container such as a drawer of a desk, or of a chiffonier, or in a recess in a wall.

The selenium cell may be protected from the room lights by so arranging a contact on the lighting switch that, when the room lights are turned on, the power circuit f)f the apparatus is opened. This will prc\ent the setting off of the apparatus when the room lights are in u.se, but will in no way impair its effectiveness in the case of another light when the room lights are switched off. The apparatus may be protected from daylight by some simple form of time switch. A switch of this kind can be improvised easily from an old alarm clock, b%- fit- ting the clock with a circular conduct- ing plate which will come into con- tact with the hour hand during a designated portion of the night. Should it be desired to

��leave the apparatus untouched for longer periods ot time, clockwork mechanisms, which will run for the desired |)eriod of time, maybe used. The revolution of a contact arm once in each twenty-four hours is necessary. A contact arm can be arranged which would cause the thief- catcher circuit to be opened say from five .\. M. to seven V. M., or during theda\light hours. Another variation would be to util- ize a second selenium cell well-exposed to daylight, which, when illuminated, would cut out the thief-catcher apparatus, by operating a relay connected to a break switch. Such an apparatus would be simple in mechanism and shoultl otTer no difficulties to the experimenter.

���A machine for developing ami [u 11111115; negatives taken in the field by scouts

��Field Photograph Kit for the Use of the Artillery

A FEW )ears ago the Signal Corps undertook the task of developing a photographic outfit that could be carried with a mobile army. After much experimenting a field telephoto equipment was designed which contained everything necessary for developing and printing ncgatixes taken in the field by- scouts.

A machine was obtained for projecting lantern-slides in a wall-tent, so that the commanding general could see on a large scale the surrounding coun- try, etc. The tele- photo-camera has proved somewhat useful in photo- graphing the location of shots in field artillery work. When set up for developing and printing the kit re- sembles a suitcase on tripods. Two windows are pro- \idixl. One admits red light for devel- opingand theother white light for printing. The kit has not >et been adopted as a unitof arnn equipment.

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