THE ELECTRIC TELEGKAPH. 



back of the post. So many as thirteen of these supports may be 

 seen upon some of the posts of the North- Western line near 

 London. The wires supported on some of these are continued to 

 Liverpool and Manchester, and some even to Glasgow. 



54. If the same wire were carried over a succession of supports 

 for a certain distance, they would after a certain time become 

 slack and hang in curves between post and post. This would be 

 attended with great inconvenience and confusion, inasmuch as 

 one wire especially when agitated by wind would come in con- 

 tact with another, so that the currents running along them would 

 pass from one to another, and the proper signals conveyed by 

 such currents would no longer reach their destination. 



To prevent this, apparatus for tightening the wire are on all 

 such lines provided at convenient distances, such as half-a-mile, 

 upon posts which are thence called winding posts. These posts 

 are of larger dimensions than the ordinary posts. A grooved 

 drum, on which the wire is wound, is attached to them by a bolt, 

 which passes through the post, but clear of the wood. Upon this 

 bolt is fixed a ratchet wheel by which the drum may be turned 

 in one direction, so as to coil the wire upon it, with a catch which 

 prevents its recoil in the other direction, and therefore maintains 

 the tension of the wire. The bolt is kept from contact with the 

 post by passing through a stoneware collar. 



The current passes through the winder and the bolt, these 

 being metallic, but in case of any interruption arising from the 



Tig. 12. 



oxydation of their surfaces a supplemental piece of conducting 

 wire is provided, which connects the main wires at points taken 

 above and below the winding post, as represented in fig. 12. 

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