254 SCIENCE OF HOME AND COMMUNITY 



in the engine. On each car connected with the tank is a 

 cylinder provided with a piston which connects with a brake. 

 The engineer is able to control the working of all the brakes, 

 and by turning a cock the compressed air is caused to enter 

 each cylinder, pushing out the piston which sets the brakes. 



Railway signals. In order to lessen the possibility of 

 accidents various systems of signals are used so that the 

 engineer may know whether any other trains are near his. 

 The railroad tracks are divided into blocks, or sections, of a 

 few miles in length. At the beginning of each block are 

 signals, used to indicate whether any train is in that block. 

 No train is supposed to enter a block till the previous train 

 has left it. Levers are attached to posts by the side of the 

 track, and by their position they indicate whether a train 

 is in the block. These levers may be operated by signal 

 men, or automatically by electricity. The weight of the 

 train on the rails closes a circuit, which operates the signal. 

 On a double-track road, the engineer is concerned only with 

 those trains which are going in his direction, but on the 

 single-track road, he is also concerned with those coming 

 from the opposite direction. 



Train dispatcher. The trains are controlled by a train 

 dispatcher, who is connected by telegraph with every rail- 

 road station. He keeps a careful record of the position of 

 every train. The telegrapher at each station informs the 

 dispatcher when each train leaves his station. Ordinarily 

 the trains run on a scheduled time, and each engineer and 

 conductor knows where he is expected to be at any given 

 time and what right of the road he has. But when a train 

 becomes delayed, the schedule is interfered with, and the 

 trains are then run by special word from the dispatcher, 

 who sees that proper places are assigned for meeting other 

 trains, with as little danger and loss of time as possible. 

 These orders for the trainmen are telegraphed to the teleg- 

 raphers at the stations and given by them to the conductor. 



