Popular Science Monthly 



429 



5T0RA&E: BATTtRY 



RELAYS 



DRY BATTC^' I 



A perspective view of the dog showing his internal mechanism. In the insert, a diagram 

 showing the construction of the steering solenoids 



may suddenly refuse all the inducements 

 offered by the master with his pocket 

 flashlight and turn his entire 

 attention to the pursuit of 

 the window. 



The principal adjustment 

 is that of equal sensitiveness 

 of both selenium-cell-relay 

 units. It is practically im- 

 possible to obtain two selen- 

 ium cells having equal 

 resistances and equal sensi- 

 tiveness, and therefore dif- 

 ferent applied voltages and 

 different tensions in the back 

 springs of the relays are 

 necessary, in order that both 

 will operate at the same in- 

 stant when influenced by 

 the attracting light, and that 

 both will release at the same 

 instant when the light is ex- 

 tinguished, or when it be- 

 comes too weak to effect 

 operation. 



With selenium cells made 

 sensitive only to definite 

 colors or wavelengths of 

 light, it is possible to make 

 the dog back away with one 

 light and be attracted by an- 

 other. Cells can be given a 



certain amount of inherent color sensi- 

 tiveness, but this is best secured by 



O 



LIGHT 



A simplified dia- 

 gram illustrating 

 the principle of the 

 dog's construction 



means of ray filters which 

 allow only definite wave- 

 lengths to pass. Another 

 means of making the dog 

 sensitive to only one source 

 of light is to cause that light 

 to be interrupted by means 

 of some form of shutter, in 

 conjunction with selective 

 elements on the dog which 

 will not allow the sensitive 

 relays to be closed unless the 

 fluctuations in the trans- 

 mitted light correspond ex- 

 actly with the frequency of 

 the selective element. 



It is obvious that if we 

 make the dog a boat instead 

 of a wheeled vehicle, and if 

 we provide the boat with a 

 forward compartment filled 

 with gun cotton, we would 

 have a torpedo of the kind 

 described and pictured else- 

 where in this issue. A 

 searchlight on board a ship 

 would serve to guide the tor- 

 pedo on its course of destruc- 

 tion throusrh the water. 



