and its application to Fire Alarms. a 
cross-connection would complete a circuit. Between the differ- 
ent Stations the wires diverge widely, and at Stations where they 
may come together for the purposes of signalizing, they are care- 
fully protected. Hence false alarms, by an abuse of the wires, 
are rendered nearly impossible. 
Another important result from the exclusive use of wires is 
double insulation. If the ground were used there would be only 
one insulator between it and the wire above, forming part of the 
same circuit, but, with wire conductors alone, there are two insu- 
lators, besides the buildings and intervening ground, which the 
current must traverse to make the circuit complete between cor- 
responding ‘conductors. Another useful result of the same ar- 
rangement is that the ground is left as a reserve, and can be used 
temporarily with a separate battery for special police communica- 
tions, in connection with, or addition to, both of the Signal wires. 
As the insulator forms an important part of every Telegraphic 
System, the form used in the con- 
struction at Boston, which is Batch- 
elder’s patent, is shown in fig. 1. 
Preserve the insulation. ‘The wires pass over the top of the insu- 
Port in cities for the conductors carried through the air, the use 
be resorted to 
. Cities, may be estimated at from $600 to $1,000 per mile. ae 
, 2; i of action as well as for purposes oF st 
ee bus 
