206 THE PHYSICAL GEOGRAPHY OP THE SEA. 



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 " 



435. 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. 



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

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

 places named (^ 428) 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. 



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

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

 be weighed. In this state of the case. Passed Midshipman J. M. 

 Brooke, United States Navy, who, at the time, was associated 

 with me on duty at the Observatory, proposed a contrivance by 

 which the shot, on striking the bottom, would detach itself from 

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

 contrivance, called Brooke's Deep-sea Sounding Apparatus, is 

 represented in Plates II. and III. opposite. 



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 con- 

 trivance specimens of the bottom have been brought up from the 

 depth of more than two miles. 



438. The greatest depths at which the bottom of the sea has 

 been reached with the plummet are in the North Atlantic Ocean, 

 and the places where it has been fathomed do not show it to be 

 deeper than twenty-five thousand feet. 



The deepest place in this ocean (Plate XL) is probably between 

 the parallels of 35° and 40° north latitude, and immediately to the 



* A Stellwagen cup is found to answer better. 



