Staff-Commander J. E. Davis on Deep-sea Thermometers. 133 



and as it was known that a delicate thermometer was affected in 

 vacuo, it was natural to suppose that an opposite effect would be had 

 by placing them under pressure, and particularly such as they would 

 be subjected to at great depths. 



Several thermometers, of a superior construction, were made by 

 different makers, and permission was granted to make experiments by 

 pressure in an hydraulic press ; but much delay was caused by not 

 being able to obtain a press suitable to the requirements, until Mr. 

 Casella, the optician, had a testing-apparatus constructed at his own 

 expense, and the experiments were commenced. 



Previously to the experiments being made, Dr. W. A. Miller, 

 V.P.R.S., proposed, or rather revived, a mode of protecting the bulb 

 from compression by encasing the full bulb in glass, the space between 

 the case and the bulb being nearly filled with alcohol*. 



A wrought-iron bottle had been made to contain a thermometer, 

 for the purpose of comparison with those subjected to compression ; 

 but it failed, and finally burst under great compression ; it proved, 

 however, of but little consequence, as those designed by Dr. Miller 

 showed so little difference under pressure that they were at once ac- 

 cepted as standards. 



Two series of experiments were then most carefully made, at pres- 

 sures equal to depths of 250, 500, 750, &c. to 2500 fathoms, the 

 results of which satisfactorily proved that the strongest-made unpro- 

 tected thermometers were liable to considerable error, and therefore 

 that all previous observations made with such instruments were in- 

 correct. 



Experiments were also made in the testing-apparatus with Sir Wm. 

 Thomson's enclosed thermometers, to ascertain the calorific effect 

 produced by the sudden compression of water, in order to find what 

 error, if any, was due to compression in the Miller pattern : an error 

 was proved to exist, but small, amounting to no more than 1 0, 4 

 under a pressure of 3 tons to the square inch. 



The dredging-cruise of the ' Porcupine' afforded an opportunity of 

 comparing the results of the experiments made in the hydraulic test- 

 ing-apparatus with actual observation in the ocean, and a most 

 careful series of observations were obtained by Staff-Commander E. 

 K. Calver at depths corresponding to the pressure applied in the 

 testing-apparatus ; the result was, that although there was a differ- 

 ence in the curves drawn from the two modes of observation, still 

 the general effect was the same, and the means of the two were 

 identical. 



From these experiments and observations a scale has been made 

 by which observations made by thermometers of similar construction 

 to those with unprotected bulbs can be corrected and utilized, while 

 it is proposed that by means of observations made with the Miller 

 pattern in the positions and at the same depths at which observa- 

 tions have been made with instruments not now procurable for actual 



* Phil. Mag. November 1869. 



