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 Fig. 43. Two thimbles F F pass 
through the two ends of the heavy oval brass shield 
AA; 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 B 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 
