in the Twenty Years before 1895 47 



I line on June 18, 1875. It may be added that, during the 

 whole voyage, eleven thermometers collapsed under the high 

 pressure, at very great depths. 

 We see then that, at a full station of average depth the 

 length of sounding line handled was: 

 For the sounding . . . . . . 2060 fathoms 

 For intermediate temperatures . . 2500 

 And for intermediate waters . . 1875 



Total .. .. 6435 

 When the depth was 3000 fathoms or more the length of 

 sounding-line handled in the day amounted to from 7500 to 

 8000 fathoms. In addition to this there would be the 3000 

 fathoms of dredge-line. 



In dredging and trawling the "Challenger" was equally 



successful. From the date of sailing from England to October 3, 



1873, or nine months, the dredge or trawl-line parted six times. 



From October 3, 1873, till June 26, 1875, 113 stations, no line 



parted. In 1875 three lines, and in 1876 two lines parted. 



.11 during three-and-a-half years, during which 354 stations 



re made, there were only eleven cases of the parting of the 



dredge or trawl-line. 



In the ordinary routine on board the "Challenger" the 



sounding was made with a sinker weighing 336 Ibs. The 



"Baillie" tube which carried it weighed 25 Ibs., and the water 



bottle weighed 20 Ibs., so that the total weight at the end 



of the line was 381 Ibs. in air. Excepting the water bottle 



which was of bronze, all this weight was of iron, and we find 



weight in water by deducting one-eight or 48 Ibs. which 



65 333 Ibs. as the effective sinking weight. The No. i lin< 



which was in daily use, weighed in water 6 Ibs. per 100 fathoms 



(in air it weighed 20 Ibs.). Therefore, every 100 fathoms of 



used in the sounding added 6 Ibs. to the effective sinking 



weight, but at the same time by it- in. HMD it produced a 



nl itmn which depended on the velocity of descent. The 



retarding effect, except in very shallow water, is greater th.tn 



tin ,i< (. ''licet, therefore the net effect is one of retarda- 



\\ith win the opposite is the case. After the 

 50 or 100 fathoms of line have run out, th i j, .1 continual 



