NATURAL PHILOSOPHY. 107 



for these two functions ; one, the signal circuit, and the other the 

 alarm circuit. Comparing the municipal telegraph to the nervous 

 system of man, these circuits correspond respectively to the sensitive 

 and motor nerves. A single agent at the centre controls the whole 

 system, receiving the indication of a fire by the signal circuit, and 

 throws the current of the battery on the alarm circuit at will. In the 

 course of the signal circuit are forty signal stations, consisting of locked 

 cast-iron boxes, placed on the outside of buildings, and in charge of 

 suitable persons. In case of fire, one of these is opened, and a crank 

 within it turned a few times. The axis of this crank carries a circuit 

 wheel, which communicates to the central office the number of the 

 district and station striking them upon a bell, and also recording 

 them permanently on a Morse register. The agent of the office imme- 

 diately depresses the appropriate key of the district keyboard connected 

 with the alarm circuit. The keyboard has a key for every district 

 signal which is to be struck on the bells. When the key is held down, 

 a circuit cylinder revolves beneath it, completing the circuit at the 

 precise intervals requisite to strike the signal of the district with suit- 

 able intermissions. This action of the current liberates each time the 

 detent of a powerful striking machine at each belfry or alarm station in 

 the circuit, so that a single blow is struck synchronously upon each 

 bell. The Boston nineteen alarm-bells are thus telegraphically con- 

 nected. The machines are carried by weights, varying from 800 to 

 2000 pounds. The detents of these machines are liberated by a falling 

 arm, which is set off' by the attractive force of an electro-magnet. This 

 beautiful device, by which an immense saving of electro-magnetic 

 power is obtained, is due to Mr. M. T. Farmer, the constructor of the 

 system, to whom, also, many of the adaptations and details of arrange- 

 ment in the system are to be ascribed. In the central office is an 

 alarni-bell register, which shows the number of blows struck upon the 

 bells. There is also a testing-clock, which tests each circuit automat- 

 ically once an hour ; all the batteries employed in the system are also 

 at the central office. In each signal box there is a little electro-mag- 

 net and armature, whose click enables police or other communications 

 to be transmitted from the central office to the signal stations, while a 

 signal key in the box allows return communications to be made. At 

 each signal and alarm station, sixty in all, discharges of atmospheric 

 electricity are provided with a ground connection. This affords inci- 

 dental protection to the city from lightning. The circuits comprise 

 forty-nine miles of No. 8 and 10 wire of Swedish iron. To prevent irreg- 

 ularities, the ground is not used as part of the circuit. Between each 

 station there are always two wires following widely different routes. 

 If one is accidentally broken it occasions no interruption of the circuit. 

 The buildings, for the support of the wires, are carefully selected. 



The signal and alarm circuits in Boston are, for various reasons of 

 economy and security, increased in number to three of each class. 

 These are the North, South and South Boston Circuits. By an 

 arrangement of the District key-board, the current from the battery is 

 thrown momentarily in rapid succession on each of the three alarm 



