Page:Popular Science Monthly Volume 69.djvu/435

Rh telephones. Upon placing the ear against the lid of the box the articulation of the person speaking into the membrane telephone was audible, proceeding from the lid (Fig. 2). A fourth form of

speaking telephone was shown, intended to be used only as a transmitter. It consisted of a metallic ring supported horizontally, carrying a stretched membrane, to the center of which was fastened a platinum wire clipping into a little cup containing acidulated water and was referred to as the liquid transmitter (Fig. 3). In addition

to these telephones, one of Koenig's manometric capsules was shown, arranged for studying optically the peculiarities of the electrical current generated by the movements of the membrane in the telephone.

Of telegraphic and signaling apparatus there was an excellent display at the Centennial, as well as a historical collection of great value showing the evolution of magnetic and electric signaling. But of other electrical apparatus there was only a meager display. All was included in Group XXV., Instruments of Precision.