and its application to Fire Alarms. 7 
shown ath. The hammer represented in the figure is usually 
placed in a belfry above, connected with the hammer lever by a 
Wire. 
The bells to which the striking machines are applied in Bos- 
ton, vary in weight from 3,700 to 300 Ibs. The machines are of 
uniform size, but they are carried by weights, varying from 2000 
to 800 lbs., on a single chain. It was supposed in the outset that 
a blow equal in force to that of the common tolling hammers, 
would be sufficient for all the purposes of alarm, especially as, in 
the Telegraphic System, an alarm is not propagated by sound, 
from bell to bell, as in the ordinary method. A greater amount 
of sound was however considered desirable by members of the 
Fire Department, and a great addition to the force of the ham- 
mer was found necessary to produce adequate vibration in the 
largest bells. 'Thus the hammer, judged suitable for the bell of” 
Brattle St. Church, weighs forty pounds, has a handle three and 
ahalf feet long, swings through an are of four'and a half feet, 
and is moved at each blow by a force equal to a weight of 1440 
Ibs., falling one inch. To liberate the detent of a machine of 
this power, the weight on the falling arm must be proportionally 
icreased, and the electro-magnetic power required to free the 
arm will amount to abont 14,000 grains when the armature (faced 
with brass) is in contact with the electro-magnet. ‘The battery 
provided at the Central Office must be adequate to produce this 
effect through the Alarm Circuits. d 
The striking machines are calculated to strike 1000 blows with 
a fall of the weight equal to 83:33 feet on a single chain, that is, 
at the rate of one inch to a blow. Where a great expenditure of 
power is required, and the weight is applied by a single chain with 
a limited fall, the number of blows which can be obtained from 
a single witiding is necessarily diminished. ‘Thus the number of 
blows with the three largest bells in Boston, will not probably 
exceed 450 or,500. Fortunately these bells are near the Central 
Office, and can be easily wound up when the Alarm Bell Register, 
Fepresented in fig. 7, indicates that they are nearly run down. — 
The striking machines should be wound weekly, and a detailed 
feport made, by the person winding them, to the Central Off 
Where it should be entered on the journal. All intermediate 
Windings should be entered in a similar manner. aes 
_ The time required between successive blows of the Striking 
Machines is two seconds. The revolution of the cylinder in the 
District Key-board, fig. 6, should be graduated so as to ¢ | 
the cirenit, for consecutive blows, at precisely this interval. _The 
average number of blows, in striking District Signals with inter- 
Vals of five seconds after each Signal, is about twenty per minute. 
From fifty to a hundred blows would be sufficient, orainarny, © 
