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



In this case the timing was only valuable as cor- 

 roborating other evidence of the accuracy of the 

 sounding, for even at this great depth, nearly three 

 miles, the shock of the arrest of the weight at the 

 bottom was distinctly perceptible to the commander, 

 who passed the line through his hand during the 

 descent. This was probably the deepest sounding 

 which had been taken up to that time which was 

 perfectly reliable. It was taken under unusually 

 favourable conditions of weather, with the most 

 perfect appliances, and with consummate skill. The 

 whole time occupied in descent was 33 minutes 

 35 seconds ; and in heaving up, 2 hours 2 minutes. 

 The cylinder of the sounding apparatus came up 

 filled with fine grey Atlantic ooze, containing a con- 

 siderable proportion of fresh shells of Globigerina. 

 The two Miller- Casella thermometers registered a 

 minimum temperature of 2*5 C. 



Various attempts have been made to devise an 

 instrument which should determine accurately the 

 amount of vertical descent of the lead by self-regis- 

 tering machinery. The most successful apparatus for 

 this purpose, and the one most in use is ' Massey's 

 sounding-machine.' This instrument, in its latest and 

 most improved form, to be used with the common 

 lead, is shown in Pig. 43. Two thimbles FF pass 

 through the two ends of the heavy oval brass shield 

 A A ; to the upper of these the sounding-line is 

 attached, and to the lower the weight at about half 

 a fathom .from the machine. A set of four brass 

 vanes or wings u are soldered obliquely to an axis 

 in such a position that as the machine descends the 

 axis revolves by the pressure of the water against 



