152 SATURDAY LECTURES. 



in the line, which in dredging would otherwise require the 

 labor of many seamen. 



The operation of sounding is sufficiently simple, and re- 

 quires no explanation. A thermometer is usually attached 

 to the line at a short distance above the lead or sounding 

 cup. If serial temperatures are desired several thermome- 

 ters may be attached to different parts of tlie line, or several 

 water bottles if water samples are required. 



In dredging or trawling the dredge or trawl is lowered to 

 the bottom by a line of sufficient strength. This, in the 

 work of the Coast Survey, is of wire rope, as suggested by 

 Prof. Alex. Agassiz, which, as compared with the rope used 

 on the Challenger expedition, saves much friction, much 

 room in stowing on the vessel, and easier handling, with no 

 loss of strength, and a great gain in the time occupied in 

 reaching the bottom and hauling in. In order that the 

 motion of the vessel in drawing the dredge over the bottom 

 may not tend to raise its mouth off the bottom, a weight is 

 usually attached to the line at some distance in advance of 

 the dredge and some slack line is run out, the resulting po- 

 sition of the ship, weight, and dredge being shown on the 

 diagram exhibited. 



On the 1st of September, 1818, Sir John Ross, R. N., ran 

 out 1,000 fathoms of line, and in the mud, brought up by 

 the sounding-cup, were tubicolous worms, while at 800 

 fathoms was entangled a fine brittle star-fish, sometimes 

 known as a " Medusa's Head " on account of its many arms. 

 This shoAvs that the actual depth could not have exceeded 

 800 fathoms (since star-fish do not swim,) and was probably 

 less, but it is the first recorded instance of the capture of 

 animals from any such depth. 



In 1817, Sir James Clarke Ross, R. N., published an ac- 

 count of his antarctic voyage, in Avhich he states that seve- 

 ral shell-fish Avere brought up from 1,000 fathoms on that 

 expedition, and that he believes the bed of the ocean to 

 be teeming Avith animal life. 



■ In spite of such testimony the existence of life on the sea 

 bottom, at a depth beyond tAvo or three hundred fathoms^ 



