DEVELOPMENT OF TELEPHONE SERVICE 



43i 



brane 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 



Bell's Centennial Iron Box Magnet Receiver. 

 Fig. 2. 



speaking telephone was shown, intended to be used only as a trans- 

 mitter. It consisted of a metallic ring supported horizontally, carry- 

 ing 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 



G^> 



Bell's Centennial Liquid Transmitter. 

 Fig. 3. 



to these telephones, one of Koenig's manometric capsules was shown, 

 arranged for studying optically the peculiarities of the electrical cur- 

 rent generated by the movements of the membrane in the telephone. 

 Of telegraphic and signaling apparatus there was an excellent dis- 

 play 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. 



