

THE ELECTRIC CONDUCTIVITY OP NITRIC ACID. 



377 



was experienced in obtaining silence in the telephone within the limits desired. This 

 was eventually traced to imperfect insulation of the wooden board, even though well 

 seasoned and previously soaked with paraffin wax (figs. 2 and 3). It was there- 



Fig. 2. 



Fig. 3. 



. 



fore thought desirable to construct a bridge in which the wire was an airline, and all 

 the strappings were mounted upon ebonite pillars. The wire was stretched between 

 two massive brass castings, aa, and insulated from them by ebonite plates, bb ; at one 

 end it was fixed to a brass pin, and at the other to a stretching screw, s', so arranged 

 VOL. cxci. A. 3 c 



