and its application to Fire Alarms. 75 
these notes were omitted it would at once be perceived. ‘Taken 
together, the chime would furnish hourly assurance of the integ- 
rity of all the Circuits of the System. 
r. Farmer has also devised a method of testing, by means of 
his electro-magnetic clock, affording equal facilities with the 
mode which has been described. Once each hour the current is 
thrown, by successive oscillations of the seconds pendulum, upon 
as many circuits as it is desired to test. ‘This method gives ob- 
viously a very wide range, both as to number of circuits and the 
intervals of time at which the application can be made. 
tricity, connected with the ground,—and, where required, the 
Switch for shutting off the current from the striking machipery, 
when the bell is rang by hand. 
‘The weight, train of wheels and hammer of the Striking Ma- 
chine, are identical in character with the corresponding part 
church clocks,—the machine being so arranged, however, as to 
strike only once each time that the detent is removed. Greater 
power is required to liberate this detent than can be directly or 
teadily obtained by means of an electro-magnet, placed in the 
Alarm Circuit, and actuated by the Alarm Battery at the Central 
Office. Two modes of obtaining an increase of power, for this 
Purpose, exist ; one, by including in the Alarm Circuit a receiving 
tagnet, which brings into action a local battery, operating the 
electro-maynet by which the detent is liberated, In this case the 
| battery may consist of three or four pairs of the odds an 
ends form, which, in an open circnit, need no care for several 
Weeks, if not mouths, ata time. The other mode is by employ- 
Ing some secondary apparatus, liberated by the electro-magnet 1n 
the Alarm Circuit, to raise the detent. This method was applied 
y Mr, Farmer in 1848, in his very beautiful instrument, which 
Which will how be described. a 
ig. 9(see next page) represents the precise form of the Striking 
lachines, constructed by Howard & Davis, for the City of Boston, 
The frame is a most substantial casting. The electro-magnet W) 
Teadily be recognized, with its armature attached to au upright 
Ver atc. The legs of the electro-magnet consist of half-inch 
bolt, iron, surrounded with coils of insulated copper ware 
Which are three inches long and two inches in diameter. 4 
ing arm, weighted at the top, which is supported in an upng® 
*sition by a horizontal lever, resting on the top of the armati 
vet at 6, When the armature is attracted to the mag 
oe 
A a oa Gel 
