THE ELECTRIC TELEGRAPH. 



No adaptation of the system can be more interesting and useful 

 than that which is made for the purpose of conveying signals of 

 alarm and intelligence in the case of fire. 



This system has been very completely developed in Boston. 



The city is divided into seven districts, each provided with a 

 powerful alarm bell. Every district contains several stations, 

 varying in number according to its size and population, There 

 are altogether in the seven districts forty-two stations. All these 

 stations are connected with a chief central office, to which intelli- 

 gence of fire is conveyed, and from which the alarm is given ; two 

 telegraph wires are employed, a return wire being used to com- 

 plete the circuit, and provide as completely as possible against 

 accidental interruption or confusion. 



At each of the forty- two stations, which are placed at intervals of 

 100 rods throughout the city, there is erected in some conspicuous 

 position a cast-iron box containing the apparatus for conveying 

 intelligence to the central office. The box is kept locked, but the 

 key is always to be found in the custody of some person in the 

 neighbourhood, whose address is painted on the box door. 



On opening this door, access is gained to a handle which is 

 directed, by a notice painted above it, to be turned slowly several 

 times. The handle turns a wheel that carries a certain number of 

 teeth, arranged in two groups, the number of teeth in one repre- 

 senting the district, in the other, the station ; those teeth act upon 

 a signal key, closing and breaking the circuit connected with the 

 central office, as many times as there are teeth in the wheel. 

 Signals are thus conveyed to the central office, and, by striking 

 the signal bell a certain number of times, the district and station 

 from which the signal is made is indicated. 



An attendant is always on the watch at the central office, and 

 on his attention being called to the signals by the striking of a 

 large call bell, he immediately sets in motion his alarm apparatus, 

 and by depressing his telegraph-key, causes all the alarm bells 

 of the seven districts to toll as many times in quick succession 

 as will indicate the district where the fire has occurred, the alarm 

 being repeated at short intervals for as long a time as may be 

 necessary. 



The signal-boxes erected at the stations contain, in addition to 

 the signal-handle, a small electro-magnet, an armature, and a 

 signal-key, so that full and particular communications can be 

 made between each box and the central station, the clicks of the 

 armature forming audible signals. They have also an apparatus 

 called a ''Discharger of Atmospheric Electricity," for preventing 

 the occurrence of injuries during thunderstorms. 



By this system certain information is given to the central office 

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