220 THE DEPTHS OF THE SEA. [CHAP. v. 



of its cylinder. As the instrument runs down the 

 water passes freely through the tube and valves, and 

 pours out by the holes in the wall of the cylinder. 

 When it touches the ground the piston is pulled 

 down by the weight, but its progress is somewhat 

 arrested by the water in the lower part of the 

 cylinder, which can only escape slowly, thus giving 

 the weight time to force the terminal chamber with 

 the butterfly valves into the ground. The weights 

 then rest upon the bottom and relieve the spring 

 which throws the sling off the tooth. The tube 

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

 chamber filled with the substance of the bottom, and 

 the other chamber with bottom water. 



In the skilful hands of Captain Calver the ' Hydra' 

 never once failed, and from the great weight used it 

 is admirably suited for accurate soundings in deep 

 water ; but it is somewhat complicated, and it brings 

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

 the cruise of the ' Porcupine/ where the large dredge 

 was sent down at almost every sounding-station, this 

 was of little consequence ; but where dredging is im- 

 practicable, and all information as to the condition of 

 the bottom must be got from soundings, some simple 

 adaptation of the < Bull-dog ' scoops or the Fitzgerald 

 apparatus would certainly have a great advantage. 



During the cruise of the ' Porcupine ' in 1869 

 soundings were taken with the utmost care at ninety 

 stations, and in 1870 at sixty-seven stations, and on 

 every occasion the operation was conducted by Capt. 

 Calver himself, whose great experience on the sur- 

 veying service was in itself a guarantee of the greatest 

 possible accuracy. Captain Calver told me that on 



