66 THE VOYAGE OF H.M.S. CHALLENGER. 



the weight of the sounding line plus the impetus given it by the descending sinkers 

 will be dragging the line off the reels. Directly, therefore, a sudden lengthening of 

 the intervals was observed it was known that the sinkers were at the bottom, and the 

 heaving in of the line was commenced by bringing it to the drum of the donkey- 

 engine. Care was taken not to heave up too quickly at first, and also to keep 

 the ship carefully in position over the line, for if allowed to fall off, the wind drifting 

 her to leeward, brought an unnecessary strain on the sounding line. When hove up, the 

 water bottle and thermometers were taken off, and the lower part of the cylinder of the 

 sounding rod unscrewed and its contents carefully preserved. 



The preceding table shows the rate of descent of the sounding lead from 500 to 3000 

 fathoms, and being the mean of a great number of observations, will probably be useful 

 to surveyors taking deep-sea soundings with apparatus similar to that used on board 

 the Challenger, as any great difference from the numbers therein given would show 

 either that the weights were at the bottom, that the line was incorrectly marked, or that 

 a current was affecting it. 



The time-intervals observed in seven of the exceptionally deep casts obtained by the 

 Challenger are given in the following tables, from 1000 fathoms to the depth obtained; 

 five of them with 4 cwt., and two with 3 cwt., of sinkers attached. 



It may be as well to remark here that although only the time each 100 fathom mark 

 entered the water, and the intervals between these times are given in these tables, in 

 actual practice the time each 50 fathom mark entered the -water was registered when 

 2000 fathoms of line had been paid out, and the time each 25 fathom mark entered the 

 water when 3000 fathoms had run out, so that it was possible to detect at once when the 

 sinkers reached the bottom. 



[Table of Challenger Soundings. 



