MECHANICAL EQUIVALENT OF HEAT. 135 



obtained by the addition of water to water, while X. 

 gives the mean of the different methods, and XI. gives 

 the values as deduced from the formula — 

 Ct= 1-006630 -0-000593962/ 



+ o-ooooo433865o/ 2 +0-000000425 5 20/ 3 



— 0-0000000028 1 gt*, 

 the unit being (I am glad to see) the capacity for heat 

 of water at 15 C. 



I quote the numbers given in Cols. VIII., IX., XL 

 for each five degrees of temperature only. 



(No direct observations appear to have been taken 

 above 31", and therefore the value at 35 is exterpolated.) 



It does not appear to me that the numbers given in 

 Cols. VIII. and IX. (which sum up the whole of the ex- 

 perimental evidence at the temperatures quoted) justify the 

 use of such a formula as that given above ; at all events 

 experimental results such as those at temperatures o°, 5 , 

 2 5 , and 30° seem scarcely capable of a strain 1 which is 

 too great for any physical measurements that I am 

 acquainted with. 



The experimental results are of great value, the more 

 especially as it is evident that the observers devoted 

 much time and attention to the standardisation of their 

 thermometers. 



The experiments themselves agree with the formula 

 in giving a minimum value at about 20 C, and on this 

 point, therefore, the authors differ widely from both 

 Rowland and myself. 



1 For example, Col. VIII. gives 1 + -000025 (6 - 15) as the capacity 

 for heat over the range 15 to 25 C, while Col. IX. gives 1 - -000014 

 ($- 15) over the same range. 



