Popular Science Muiif/ili/ 



759 



sistanct's are shown in tlie separate 

 circuits for tiie purpose of reguiatiiiii tiie 

 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 tliis 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 tlie 

 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. 



