REPORT ON THE PRESSURE ERRORS OF THE THERMOMETERS. 3 



Captain Dar>* Jl/<xfe of Testing ; and his Correction for the Maximum Side. (With 

 this Appendix C. Heating of Water by Compression.) 



Consequent Correction for the Minimum Side. 



Theoretical Determination of the Direct Effect of Pressure. Experimental Verifica- 

 tion. (With this Appendix A, On the Accurate Measurement of High Pressures.) 



The Aneurisms. Their Object and Effects. (With this Appendix B. Calculation 

 of the Effect of an Aneurism.) 



Imploding and Exploding of the Thermometer Bulbs. 



Description of the Apparatus for applying Pressure. (Extended in Appendix D.) 



Accurate Measurement of great Pressures. (Also Appendix A.) 



Internal Pressure Gauges. 



External Pressure Gauge. 



Results of the Experiments. The true correction for pressure is very small. 



Sources of the large effect obtained in the Press. 



Final Conclusion from the Investigation. (Detailed in Appendix E. Tabular 

 Synopsis of the General Results of Experiment and Calculation.) 



These we will now take in order. 



The Pressure-Corrections supplied to the Challenger along with the Thermometers. 



When I was first asked to examine the thermometers I judged, from the appearance 

 and nature of the protection over the bulbs, that very slight corrections only would be 

 required, even for the greatest pressures to which they had been exposed. But Sir 

 Wyville Thomson told me that a correction of at least half a degree Fahr. had been 

 assigned for them for every mile under the sea. This correction had been given him by 

 Captain Davis of the Admiralty, who had in his experiments l the assistance and advice 

 of such exceedingly able experimenters as the late Professor W. Allen Miller and 

 others. 



Hence, although it appeared to me at first sight incredible that any such correction 

 should be required for thermometers with protected bulbs, I considered it absolutely 

 necessary to try Captain Davis' experiments over again, under the same conditions as 

 those which he had adopted in conjunction with Professor Miller. My object was, of 

 course, to find out whether I could again obtain these results, and, if I could obtain 

 them, to discover what were the causes which led to their being so exceedingly different 

 from what I should have expected. I felt assured that the results were much too large ; 

 and I had therefore, if I could reproduce them, to trace the various possible causes of 

 divergence between the results of experiments conducted in a hydrostatic press and of 

 other similar experiments made at the same pressures in the deep sea. 



1 " On Deep-Sea Thermometers,* by Captain J. E. Davis, RN. (Proceedings of the Meteorological Society, April 1871). 



