SURVEYING THE ROUTE. \f 



and described by him in the Paper before the Society of 

 Telegraph Engineers already referred to. The auxiliary pulley 

 B is that to which power was applied for winding in the wire. 

 In Lord Kelvin's machine this was done by hand, and at times 

 by an endless rope and donkey engine, while in the Silvertown 

 type a small steam engine was geared to this pulley for the 

 purpose. In the original machine a form of brake was applied 

 to the drum, varied by weights suspended from the brake-strap. 

 On starting to lower with a 341b. sinker the weights on the 



Fig, 6.— Taking a Sounding. 



brake were adjusted to give a counter pull of about 101b., 

 leaving the balance of 241b. to cause descent. This effective 

 weight was maintained during the whole of the descent by 

 adding weights at intervals to counterbalance the weight of 

 wire out. The weight of the wire being 121b. per 1,000 

 fathoms, a weight on the brake equivalent to 31b. pull on the 

 wire was added every 250 fathoms out. 



The object of this adjustment was that when the sinker 

 touched bottom (thus removing 341b. ofi the wire) there wa 



