THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



s S R A R ^ 



[FIFTH SEKIES.j -* V 



JUL 







JULY 1898. ^ rENT0 ^ 



I. A Comparison of Rowland's Thermometers icith the Paris 

 Standard, and a Reduction of his Value of the Mechanical 

 Equivalent of Heat to the Hydrogen Scale. By Dr. William 

 S. Day, Columbia University, New York*. 



1. Introduction. 



THE object of the investigation described here was to 

 compare Professor Rowland's thermometers with the 

 hydrogen scale of the International Bureau and to reduce his 

 value of the mechanical equivalent accordingly. 



The mechanical equivalent of heat, as it has been defined 

 until recently, is, in the C.Gr.S. system, the value of J in the 

 equation 



T dW 



where dW is the number of ergs required, when expended 

 in heat, to raise the temperature of one gram of water dt° C. 

 on the absolute scale. The use of the expression "mechanical 

 equivalent'' in its old sense will be adhered to in this paper 

 for the sake of uniformity with Rowland's paper. This 



dW 



quantity, — x—, differs at different temperatures on account of 



the variation of the specific heat of water. 



Rowland's measurement of the mechanical equivalent in 

 1877-78 (Froc. Am. Acad. xv. p. 75, 1879) still remains as 



* Communicated by Prof. J. S. Ames. 

 Phil Mag. S. 5. Vol 46. No. 278. July 1898. B 



