L. MECHANICS AND ENGINEERING. 441 



apparatus itself may be divided into two parts, one being on 

 the engine, and the other connected with the line. Four 

 wire brushes, each pair metallically connected, are suspended 

 from the engine, one pair having a battery and bell in circuit, 

 and the other a bell. A wheel descends alongside these 

 brushes. On the line, between the rails, at such distances as 

 may be thought requisite, or in close proximity to each sta- 

 tion, a series of insulated metallic plates, in an air-tight box, 

 are laid down, each plate being from five to ten feet long. 

 By the side of each pair of plates, the ends of which are con- 

 nected by wires, is placed an electro-magnet, with wires from 

 a battery attached. The keeper of the magnet is fixed to a 

 lever by means of a pulley, and as the engine travels past 

 this lever is pressed upon by the wheel above mentioned, 

 and the keeper is forced up against the poles of the magnet. 

 Tims the semaphore arm is raised and the line effectually 

 blocked. With the view, however, to guard against a possi- 

 ble inattention on the part of the driver of an engine ap- 

 proaching the apparatus, the box is left in such a position 

 that should his engine pass over it while the signal is up the 

 alarm-bell on the engine itself is instantly rung. The first 

 engine having successfully blocked the line in the rear, pro- 

 ceeds to the next station or signal-post, where the line is 

 again blocked ; and by means of wires to the last box and 

 mechanism similar to that above described, the electro-masr- 

 net at the former station is released, the semaphore lowered, 

 and the way left clear between tliese two sections. Tims it 

 is clear that each train protects its rear^for the distance be- 

 tween each pair of plates. The line being, as it were, divided 

 into sections, each train as it enters a section instantly blocks 

 it so that no other train can follow until the first has pro- 

 ceeded without the bell beinsr runsr as a warninc:. Connect- 

 ed with this automatic electrical block system is an arrange- 

 ment by which each train can announce its approach to any 

 station, and another for giving the station-master the power 

 to stop a train by causing the bell on the engine to ring. 

 The brushes on the engine are the means by which this is 

 accomplished ; a powerful battery placed at one station, or 

 smaller batteries placed in suitable positions along the line, 

 being the agency by which the apparatus is operated. As 

 these batteries are never in circuit except when a train works 



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