THE ROYAL ARTILLERY INSTITUTION. 
155 
Establishing Communication . 
10. In establishing communication, between the different parts of the 
instrument and the battery, copper wire insulated by cotton covered with 
varnish, or gutta percha, is made use of. The main wires, or those leading 
from the apparatus to the wire targets, may be either of copper or gal¬ 
vanized iron, supported on posts in the ordinary telegraphic manner. Tig. 4. 
