Fire Alarm

Collier's New Encyclopedia (1921)

elective signaling central office for the purpose of notifying the fire department in case of fire. The instrument is usually reduced to its simplest dimensions so that people not familiar with the system may operate it. Fire-alarm boxes contain devices to make and break electric currents. There is usually a wheel provided with teeth separated by a non-conducting substance and this when turned comes in contact with a spring which opens and closes the circuit at each tooth, thus producing a signal at the central station. The number of the signal box is usually indicated by the arrangements of teeth and spaces and in that way the fire is located. Access to the crank or chain by which the signal is communicated is obtained either by a key or by twisting the door handle or by breaking the glassthis last being the method most in vogue in large cities. Telegraph instruments connecting with headquarters for the use of firemen are often attached. The signal may be registered on a Morse recording ing instrument or by some similar device. In some districts there is an apparatus by which the signal results in the ringing of tower bells or the sounding of steam-whistles. The last method, now supplemented by electricity, was formerly in general use, but the development of the electric telegraph has resulted in greater speed and in many simplifications. From the middle of the 19th century telegraph boxes have been in use in Boston, and improvements such as the non-interfering pull and successive feature have brought the fire-alarm system to its present perfection. FIREARMS. See AMMUNITION; AR- ORDNANCE; Etc.