REPORT ON THE PRESSURE ERRORS OF THE THERMOMETERS. 25 



But it does not require to be taken into account so far as the Challenger thermometers 

 are concerned. 



Final Conclusion from the Investigation. 



The final conclusion is that only one of these five causes, which are active in the 

 laboratory experiment, can affect the Challenger thermometers when let down into the 

 sea, namely, pressure. There is there no heating of water by compression ; there is no 

 heating by pumping ; there is no heating of vulcanite, because the thermometers are let 

 down so quickly in comparison with the rate of increase of pressure that each little rise 

 of temperature is at once done away with as the thermometer passes through a few 

 additional yards of water ; and the effect on the protecting glass also, for the same 

 reason, which is a heating effect on the whole, is all but done away with step by step 

 as it is produced. All these four causes, therefore, which made Captain Davis' correction 

 so much too large, are valid only for experiments in a laboratory press, and not for ex- 

 periments in the deep sea. Therefore, as a final conclusion, I assert that, if the Challenger 

 thermometers had had no aneurisms, the amount of correction to be applied to the 

 minimum index would have been somewhat less than 0'05 F. for every ton of pressure, 

 i.e., for even- mile of depth. All the thermometers which have large aneurisms have 

 had special calculations made for them, but in no case does the correction to be applied 

 to the minimum index exceed 0'14 or about ^th of a degree per mile of depth. [The 

 results of the special calculation for each thermometer are given in Appendix E. These 

 refer to temperatures about 50 F. ; for lower temperatures somewhat less correction is 

 necessary, as the part of the tube to which the effect is due is then a little shorter.] 



Various singular results were met with in the course of the experiments, especially 

 in connection with the crushing (in some cases) or the explosion (in others) of one or two 

 of the thermometers. In one of these cases the copper tube surrounding the instrument 

 was considerably distorted. I learn that the same thing occurred to the copper sheaths 

 of the thermometers which were crushed in deep water during the Challenger voyage. 

 The explanation of this occurrence will be found in Appendix D, to which I refer for the 

 description of other singular phenomena observed during the course of the inquiry. 



The preliminary experiments connected with this investigation were carried on 

 mainly by students working in my laboratory, but all the experiments on which the pre- 

 ceding conclusions were founded were carried on by myself with the very efficient assist- 

 ance of Mr R. T. Omond and of my assistant Mr Lindsay. I have been singularly fortunate 

 in having at hand the mechanical skill of Mr Chalmers and the glass-blowing skill of Mr 

 Kemp. To these able artificers I am indebted for the prompt and thorough manner in 

 which they have executed the various novel forms of apparatus required in the course 



of this protracted investigation. 



D 



