and its application to Fire Alarms. 67 
The Signal instruments are contained in a strong cast iron case, 
and connection is made between this and the Conductors on the 
top of the building by a wrought iron pipe enclosing insulated 
wires. Entire protection to the instruments and wires is thus 
obtained. T'he Committee of Construction in Boston have wisely 
decided to place these boxes on the outside of buildings, in places 
well selected, generally opposite a lamp. ese Stations are 
distributed throughout the City at distances not greater than a 
hundred rods from each other, so that no house shall be distant 
more than fifty rods from one of them. Thus there are 18 Sig- 
nal Stations in the North Circuit, 16 in the South, and 7 in the 
South Boston Circuit. : 
_ The Signal Box, belonging to the Boston System is represented 
in fig. 4. The box and door consist each of a heavy casting. 
Ra iata'a alana 
The hinges and lock are of the most substantial kind. ‘The ont- 
Side of the door has upon it the words Sicnat Station, with the 
Dumber of the Station, and a panel containing a notice of the 
ace where the key is to be found, and perhaps also an extract 
from a City Ordinance for the regulation and protection of the 
System. ‘The Signal Crank with a heavily weighted handle is 
Seen within the box at A. It was devised by Mr. Farmer and 
Myself, to obviate the irregularity which might arise from the 
Manipulation of the Signal Key by ignorant or incompetent per- 
Sos. ‘The axis of the crank carries a circuit wheel B provided 
With a number of teeth or cams, each of which, in revolving, com- 
= circuit momentarily by a sliding contact te the key 
M ese cams are divided into two groups, seen 1 INE Be 
ne on each side of the circuit wheel, the principal of 
