THE DEPTHS OF THE OCEAN. 249 



of the same shape and "weight, we at last established the law of 

 descent. Thus the mean of our experiments gave us, for the 

 sinker and twine used, 



2 m. 21 s. as the average time of descent from 400 to 500 fathoms. 



3 m. 26 s. " " " 1000 to 1100 



4 m. 29 s. " " " 1800 to 1900 " 



698. Now, by aid of the law here indicated, we could tell very 

 nearly when the ball ceased to carry the line out, and when, of 

 course, it began to go out in obedience to the current and drift 

 alone ; for currents would sweep the line out at a uniform rate, 

 while the cannon ball would drag it out at a decreasing rate. 



699. The development of this law was certainly an achieve- 

 ment, for it enabled us to show that the depth of the sea at the 

 places named (§ 688) was not as great as reports made it. These 

 researches were interesting ; the problem in hand was important, 

 and it deserved every effort that ingenuity could suggest for re- 

 ducing it to a satisfactory solution. 



700. As yet, no specimens of the bottom had been brought up. 

 The line was too small, the shot was too heavy, and it could not 

 be weighed, and if we could reach the bottom, why should we not 

 know its character ? In this state of the case. Passed ^Midship- 

 man J. M. Brooke, United States Navy, who, at the time, was as- 

 sociated with me on duty at the Observatory, proposed a contriv- 

 ance by which the shot, on striking the bottom, would detach it- 

 self from the line, and send up a specimen of the bottom. This 

 beautiful contrivance, called Brooke's Deep-sea Sounding Appara- 

 tus, is represented in Plates II. and III. on the next page. 



A is a cannon ball, having a hole through it for the rod B. 

 Plate II. represents the rod, B ; the slings, D D, with the shot 

 slung, and in the act of being lowered down. Plate III. repre- 

 sents the apparatus in the act of striking the bottom, and shows 

 how the shot is detached, and how specimens of the bottom are 

 brought up, by adhering to a little soap or tallow,* called "arm- 

 ing," in the cup, C, at the lower end of the rod, B. With this 

 contrivance specimens of the bottom have been brought up from 

 the depth of more than two miles. 



* The barrel of a common quill attached to the rod has been found to answer better. 



