NAVIGATION, 49 



explained, depend, you will perceive, upon a 

 measurement of the distance actually run, in 

 some particular interval of time, long or short. 



35. THE DEEP-SEA LEAD. The deep-sea lead 

 is about 56 Ibs. in weight, with a hollow in its lower 

 end, armed with stiff wax or tallow to bring up 

 specimens of the bottom, and is attached to a 

 rope of I \ in. circumference, and from 100 to 

 200 fathoms in length. If the depth is to be 

 found simply by the quantity of rope carried out 

 by the lead before it reaches the bottom, the ship's 

 way through the water must be as nearly as 

 possible stopped if the depth is anything more 

 than twenty fathoms. But by the introduction of 

 a " Massey Sounding Fly " l a few feet above the 

 lead, and in line between it and the rope, the 

 distance travelled by the lead through the water 

 may be measured with considerable accuracy, and 

 thus soundings may be taken from a steamer going 

 at full speed, even when the depth is as much as 



1 In the tenth edition of Raper's Navigation (1870) I find an 

 amusing statement given on the authority of the "Survey of the 

 River St. Lawrence," by Capt. Bayfiald, that "In depths exceeding 

 100 fathoms, the fly is liable to be crushed." 



VOL. III. K 



