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XXXVIII. The Expansion of Mercury between 0° 0. and 

 -39° C. By Professors W. E. Ayrton, F.E.S., and John 

 Perry, F.B.S* 



AT a meeting of the Physical Society in November 1885, 

 Mr. G. Whipple gave the Society the results of the 

 examination of thermometers down to the melting-point of 

 mercury. There was, however, no evidence as to whether the 

 contraction of the mercury was uniform, as the thermometers 

 were only compared with mercurial ones, and as, in addition, 

 we were not able to find the results of any experiments made 

 on the expansion of mercury between 0° and —39° C, its 

 temperature of solidification, we thought it desirable to make 

 a series of comparisons of a mercury-thermometer, the stem of 

 which had been accurately subdivided into equal volumes, with 

 an air-thermometer, both immersed in a bath of frozen mer- 

 cury which was allowed to gradually become warm. For 

 this purpose we borrowed a mercury-thermometer from Mr. 

 Whipple, which he was so kind as to lend us, and one of our 

 assistants (Mr. Mather) constructed a very simple form of 

 constant-volume air- thermometer, shown in the diagram. 



B B is a wooden box, at the bottom of which is a hole closed 

 * Communicated by the Physical Society : read March 27, 1886, 



