Page:Popular Science Monthly Volume 17.djvu/120

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THE electrical polyscope is a simple and ingenious apparatus for giving light in the cavities of the human body, the invention of M. Trouve, who has distinguished himself by the contrivance of several other instruments useful to physicians and involving curious applications of electricity. It consists of an energetic and constant battery, of a reservoir or secondary battery, and of parabolic reflectors adapted to the different uses to which it may be applied, which are furnished with additional mirrors or used without them. A minute platinum thread, connected with the conducting wires of the battery, is placed in the middle of each reflector. When the battery is put in action, the wire becomes incandescent. A special rheostat is provided to regulate the flow of the electricity, which plays a part similar to that of the faucet of a water-reservoir, and controls the flow of the fluid with such exactness as to permit the finest threads of platinum

PSM V17 D120 Dental cavity lighting instruments.jpg
Fig. 1. Fig. 2. Fig. 3.

to approach the point of fusion without passing it. The melting-point of the wires used having been determined in the beginning, can always afterward be avoided without trouble. A galvanometer with two circuits, in which the electro-motive force of the reservoir and that of the battery are in opposition, enables the operator to observe