472 



HENRY A. ROWLAND 



From this I have constructed the following table : 



Corrected in this way we have, 



Joule's value 



Eeduction to air thermometer 

 Reduction to latitude of Baltimore 

 Correction for sp. ht. of copper 



My value 

 Difference 



Old. 



423-9 

 1-9 



5 



7 



427-0 



427-7 



New. 



423-9 



1-7 

 5 



426-1 

 427-1 



1-0 



or 1 in 600 and 1 in 426, respectively. 



But it is evident that all the other temperatures used in the experi- 

 ment must also be corrected, and I have done this in the following man- 

 ner. The principal other correction required is in the capacity of the 

 calorimeter, and this amounts to considerable in the experiments on 

 mercury and cast-iron, where no water is used. Dr. Joule informs me 

 that the thermometer with which he compared mine was made in 1844, 

 but does not give any mark by which to designate it, although it is evi- 

 dently the thermometer called "A" by him. I shall commence with the 

 experiments of 1847. The calorimeter was composed of the following 

 substances, whose capacities I recompute according to what in my paper 

 I have considered the most probable specific heats. 



wai-o-ht Capacity accord- Most probable Most probable 

 ing to Joule. Specific Heat. Capacity. 



Water 77617 grains 77617 1-000 77617 



Brass 24800 grains 2319 -0900 2232 



Copper 11237 grains 1056 -0922 1036 



Tin (?) 363 363 



Total capacity 



81355 



81248 



