ON DEEP-SEA SOUNDING. 365 



preserved the wire, it eats away the solder, and on 

 that account they prefer to use oil. 



[Sir. W. Thomson in reply to questions that had 

 been put said] : I have been asked to explain how 

 the resistance is applied on this apparatus. I will 

 state in the first place that this form of brake was 

 patented by me in 1858. and I have used it myself 

 ever since. 



[Demonstrating the use of the brake, Sir W. 

 Thomson remarked] : The rate of change of pull in 

 the cord per radian 1 round the wheel is equal to 

 the amount of the pull at any point, multiplied by 

 the coefficient of friction. The whole tangential 

 resistance which the cord applies to the circum- 

 ference of the wheel is equal to the excess of pull 

 at one end above that at the other end of the cord. 

 I have been asked by Mr. Latimer Clark whether I 

 recover the sinker in flying soundings. Always : I 

 never lose a pound of lead if I can help it. In the 

 use of the " deep-sea lead " of ordinary navigation, 



1 " Radian " is a most valuable word, introduced by Professor 

 James Thomson to denote the angle whose arc is equal to radius. 

 It is the hitherto nameless "unit angle" of the Cambridge and other 

 mathematical books. 



