Page:Popular Science Monthly Volume 88.djvu/457

 Popular Science Monthly

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��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.

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