422 POPULAR SCIENCE MONTHLY. 



operative parts of the device becomes sufficiently strong to cause 

 it to act. A circuit breaker is simply a switch that is arranged to 

 be opened automatically by the action of a magnet, instead of by 

 the hand of the operator. The switch part of the apparatus is 

 held in place by a catch that is set much after the fashion of the 

 catch in a mouse trap — that is, so that the least pressure will dis- 

 engage it. A strong spring acts to throw the switch open, and as 

 soon as the catch is tripped by the actuating magnet the force of 

 the spring comes into action and the circuit is opened. 



The circuit breaker is a very valuable apparatus, for it fre- 

 quently happens that, through delays of one kind or another, a 

 large number of cars concentrate at one point on the road, and, as 

 all the motormen are anxious to make headway, they all start up 

 at once at the first opportunity. If there were no circuit breakers 

 at the power house the result would be that some of the generators 

 would be greatly overloaded and perhaps disabled; but, owing to 

 the presence of the circuit breakers, the actual result is that the cir- 

 cuit is broken, and then the motormen have to wait until the cur- 

 rent is turned on again. If too many of them try to start their 

 cars at the second trial the current will again stop. After two 

 or three ineffectual efforts have been made to start all the cars 

 together the motormen will conclude to go easy, and set a few in 

 motion at a time. In this way the cars will become more evenly 

 distributed along the line, and the demand for current at the point 

 of blockade will reduce to the normal amount, or nearly so, and 

 the running of the cars will continue without further interruption, 

 for the current drawn by the motors having been reduced to the 

 average amount, the circuit breaker will cease to act. 



The bus bars and all the connections between them and the 

 generators and external circuits, as well as with all the instruments, 

 are located behind the switch board. All these connections are so 

 secured that they can not come in contact with each other except 

 where contacts are required; care is also taken to prevent any con- 

 nection being made with the iron framing that supports the marble 

 slabs. The front of a switch board is generally very attractive, 

 the surface being of highly polished marble, while all the switches 

 and instruments are finely finished and, as a rule, of decidedly 

 ornamental design. 



The switch board might be looked upon as the fountain head 

 from which the entire operation of an electric railway system is 

 controlled. By the movement of one set of switches upon it the 

 generators are thrown in or out of service, and by the movement 

 of another set of switches the several branches of the road are 

 rendered active or inactive. 



