1870.] Staff- Commander Davis on Deep-sea Thermometers. 347 



consequently that the true theoretic resistance of a solid rectangular beam is 

 exactly twice that arrived at by the theory of Leibnitz, 



The strength so computed is in general accordance with the results of 

 experiments in cast iron, wrought iron, steel, and other materials, the 

 maximum strength being found in cast iron, which is one-eighth above, 

 and the minimum in glass, which is one-fourth below the calculated 

 strength. 



The author considers this treatment of the subject as arising necessarily 

 out of Dr. Hook's law "ut tensio sic vis," and that it is in effect com- 

 pleting the application of those principles which were only partially ap- 

 plied by Leibnitz. 



The paper concludes with some practical illustrations (accompanied by 

 photographs) of the effect of diagonal action. 



The appendix contains the results of experiments on the tensile, com- 

 pressive, and transverse resistances of steel. 



III. "On Deep-sea Thermometers/'' By Staff-Commander John E. 

 Davis, R.N. Communicated by Capt. Richards, R.N., Hy- 

 drographer of the Admiralty. Received April 18, 1870. 



(Abstract.) 



The results of thermometric observations at great depths in the ocean 

 not being of a satisfactory nature, the attention of the Hydrographer 

 of the Navy was directed to the defects in the construction of the Six's 

 self-registering thermometers then in use, and also to the w r ant of know- 

 ledge of the effects of compression on the bulb ; 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 w r ould 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. 



Previous to the experiments being made, Dr. W. A Miller, Y.P.R.S., 

 proposed, or rather revived, a mode of protecting the bulb from compres- 

 sion 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 dif- 

 ference under pressure that they were at once accepted as standards. 

 * Vide Proceedings of the Royal Society, vol. xvii. No. llo, June 17, 



