POPULAR LECTURES AND ADDRESSES. 



twice the depth ; but the proportion of wire to 

 depth differs according to the depth, the speed of 

 the ship, and the roughness of the sea. For the 

 first of a set of casts use a tube and read off the 

 depth by applying it to the scale of fathoms. 

 After three or four more casts use another tube, 

 and then, according to judgment, use a tube as 

 frequently as is necessary to check your inferences 

 of depths from the counter readings. The char- 

 acter of the bottom brought up on the arming of 

 the sinker is of course to be examined every time. 



