Recent Investigations on the Mechanical Equivalent of Heat. 479 



"Note on recent Investigations on the Mechanical Equivalent 

 of Heat." By E. H. Griffiths, F.R.S. Received and Read 

 June 17, 1897. 



Yesterday (June 16) I received, from Professor Ames, of Johns 

 Hopkins University, the results of an important investigation which 

 has heen carried out under the direction of Professor Rowland and 

 himself. An elahorate comparison of the thermometers used by 

 Rowland, with certain standards supplied by the International 

 Bureau, has been performed by Mr. W. S. Day. This comparison 

 has been made under conditions as similar as possible to those 

 prevalent when the thermometers were used by Rowland during his 

 original experiments. A further most elaborate comparison has also 

 been conducted by Messrs. C. W. Waidner and F. Mallory between 

 a platinum thermometer, previously standardised at Cambridge 

 (England), and Rowland's thermometers. The results of these 

 separate investigations may be regarded as in practical agreement. 



The conclusions- to which this prolonged investigation has led the 

 authors are so important that I take this opportunity of bringing 

 them before the notice of the Royal Society. Full details will be 

 given when the respective papers are published in America, but in 

 the meantime the authors have given me permission to communicate 

 their results to this Society. 



The following chart is a reduced copy of the one forwarded by 

 Professor Ames. 



It will be seen that the alteration in Rowland's values is consider- 

 able at certain temperatures. This is rendered more evident in the 

 following table. 



Schuster and 



Temp. 



Old. 



Corrected. 



Griffiths. 



G-annon. 



6°~ 



4209 x 10 4 



4204 X 10 4 







10 



4200 



4197 







15 



4189 



4189 



4199-7 xlO 4 





20 



4179 



4183 



4193-2 



4191 x 10 4 



25 



4173 



4177 



4187-4 





30 



4171 



4173 







35 



4173 



4174 







These numbers are in the C.Gr.S. system and hydrogen scale. The 

 point to which I now chiefly wish to direct attention is this — the 

 slant of Rowland's corrected curve is almost exactly similar to that 

 resulting from my own experiments. Hence the uncertainties pre- 

 viously existing as to the changes in the capacity for heat of water- 

 over the range 10° to 25° C. are greatly diminished. 



Mr. W. S, Day writes as follows : — 



