CHAP. IV. ] ST. THOMAS TO BERMUDAS. 263 
It will be seen from the table that the intervals between 
3200, 3300, and 3400 fathoms are the same, while they ought 
to have been regularly increasing. Captain Nares thought that 
the sounding-machine had probably reached the bottom, and 
that a uniform under-current might be dragging out the line. 
He accordingly commenced heaving in, but the strain on the 
accumulators at once showed that the weights on the “ Hydra” 
had not detached. At 3700 fathoms another attempt was made 
to heave’ in, but the weights were still there. Close to the 3900- 
fathom mark the line suddenly came almost to a stop; 50 fath- 
oms more were let out, and the time taken at intervals of 25 
fathoms; and the complete change of rate at once showed that 
the instrument was on the bottom. On reeling up, it was evi- 
dent from the decreased strain that the ‘“ Hydra” tube had been 
relieved of the weights, and was coming up with the instru- 
ments attached to it alone. 
Two thermometers were sent down in this sounding, and a 
slip water-bottle. The thermometers were broken, and as 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, I will briefly describe the condition of the 
thermometers when they came to the surface : 
No. 39, a valuable instrument with a small and constant er- 
ror, which we had used for some time whenever for any reason 
we required extreme accuracy, was shattered to pieces (Fig. 
70, A): 
In No. 42 the instrument was externally complete, with the 
exception of a crack in the small unprotected bulb on the right 
limb of the U-tube. The inner shell of the protected bulb was 
broken to pieces (Fig. 70, B). 
In both of these cases there seems little doubt that the dam- 
age occurred through the giving-way of the unprotected bulb. 
In No. 39 the upper part of that bulb was ground into coarse 
powder, and the fragments packed into the lower part of the 
