

220 THE DEPTHS OF THE SEA. [CHAP. 



of its cylinder. As the instrument runs down tl 

 water passes freely through the tuhe and valves, an 

 pours out by the holes in the wall of the cylinde 

 When it touches the ground the piston is pulle 

 down hy the weight, but its progress is somewfo 

 arrested by the water in the lower part of tli 

 cylinder, which can only escape slowly, thus givin 

 the weight time to force the terminal chamber wit 

 the butterfly valves into the ground. The weight 

 then rest upon the bottom and relieve the sprin 

 which throws the sling off the tooth. The tub 

 comes up free with all the valves closed, and the las 

 chamber filled with the substance of the bottom, an 

 the other chamber with bottom water. 



In the skilful hands of Captain Oalver the ' Hydra 

 never once failed, and from the great weight used i 

 is admirably suited for accurate soundings in dee 

 water ; but it is somewhat complicated, and it bring 

 up very small samples of the bottom. In the case c 

 the cruise of the ' Porcupine,' where the large dredg 

 was sent down at almost every sounding-station, thi 

 was of little consequence ; but where dredging is im 

 practicable, and all information as to the condition c 

 the bottom must be got from soundings, some simpl 

 adaptation of the ' Bull-dog ' scoops or the Fitzgeral 

 apparatus would certainly have a great advantage. 



During the cruise of the ' Porcupine ' in 186 

 soundings were taken with the utmost care at ninet 

 stations, and in 1870 at sixty- seven stations, and o: 

 every occasion the operation was conducted by Capi 

 Calver himself, whose great experience on the sui 

 veying service was in itself a guarantee of the greates 

 possible accuracy. Captain Calver told me that o: 



