NARRATIVE OF THE CRUISE. 



133 



the intervals occupied by the line in running out increased so considerably, that no doubt 

 was felt as to the accuracy of the result. The time each 50 fathom mark entered the 

 water was registered from 3000 fathoms to the bottom ; and the following intervals 

 obtained just before and after the sinkers touched the ground, may prove interesting, as 

 they show how quickly the speed of descent of the line slackens when the weight of the 

 siukers is no longer felt : — ■ 



The time the line occupied in descending the first 3800 fathoms will be found 

 on page 67. 



Two thermometers and a slip water-bottle were sent to the bottom. The 

 thermometers were broken, and the mode in which the fracture occurred is in itself 

 curious, and has an important bearing upon the use of these instruments at extreme 

 depths. A valuable instrument which had been used for some time, whenever for any 

 reason great accuracy was required, was shattered to pieces (fig. 53 A). The other 

 instrument was externally complete, with the exception of a crack in the small unpro- 

 tected bulb on the right limb of the U-tube, whilst the inner shell of the protected bulb 

 was broken to pieces (fig. 53 B). In both of these cases there seems little doubt that 

 the damage occurred through the giving way of the unprotected bulb. 



In the first case its upper part was reduced to a powder like table salt, and the 

 fragments packed into the lower part of the bulb and the top of the tube. The large 

 bulb and its covering shell were also broken, but into larger pieces, disposed as if the 

 injury had been produced by some force acting from within. The thermometer tube 

 was broken through in three places ; at one of these, close to the bend, it was 

 shattered into very small fragments. The creosote, the mercury, and bubbles of 

 air were irregularly scattered through the tube, and it is singular that each of 

 the steel indices had one of the discs broken off. The whole took place no doubt 

 instantaneously by the collapse of the small bulb, which at the same time burst the 

 large bulb and shattered the tube. 



In the other a crack only occurred in the small bulb, either through some pre-existing 

 imperfection in the glass or from the pressure. When the pressure became extreme the 



