OP ARTS AND SCIENCES. 43 



The reduction to the air thermometer was made for the tempera- 

 tures of 9*^0. and 11° C. respectively, but they both refer to the 

 temperature of the water used when the capacity was determined ; 

 this was about 9° C. Hence these experiments gave 427.5 and 428.7 

 on the air thermometer, with the water at about 9° C. 



The next experiments, with cast-iron, can be corrected in the same 

 manner, and thus become 



782.2 780.2 



and these are as before for water at 9°. 



The determination by the heating of a wire, whose resistance was 

 measured in ohms, can be thus reduced. The value found by Joule 

 was 429.9 in the latitude of Baltimore at 18°. 6 C. 



Using the capacity of the copper .0922, as I have done in my paper, 

 this quantity will be increased to 430.3. But I have given reasons 

 in my paper on the " Absolute Unit of Electrical Resistance " to show 

 that there should be a correction to the B. A. Committee's experi- 

 ments, which would make the ohm .993 earth quadrant -4- second, 

 instead of 1.000 as it was meant to be, which nearly agrees with 

 the quantity which I found, namely, .991. Taking my value .9911, 

 Joule's result will reduce as follows : — 



429.9 at 18°.6 C. 

 Correction for thermometer -f" 1-^ 



" " capacity -)- .4 



« " ohm —3.8 



Corrected value 428.0 at 18°.6 C. 



The last determinations in the " Philosophical Transactions " of 

 1878 can be reduced as follows. 



The capacity of the calorimeter was determined by experiment, 

 instead of calculated from the specific heet of copper given by Reg- 

 nault, as in the older experiments. The value used, 4842.4 grains, 

 corresponded to a specific heat of brass of about .090, which is almost 

 exactly what I have considered right. The reduction to the air 

 thermometer will decrease it somewhat, and the correction for the 

 increase of the specific heat of brass and the decrease of the specific 

 heat of water will also change it somewhat. In all, the amount will 

 be about 1 in 200. Hence the reduction becomes as follows : — 



