APPENDIX TO THE MECHANICAL EQUIVALENT OF HEAT 475 



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 : 



Joule's values 



Correction for thermometer 

 Correction for capacity 

 Correction for latitude 

 Correction to vacuum 



Corrected values 



772-7 774-6 



3-2 3-7 



2 -2 



9 -9 



773-1 



3-1 



2 



9 



767-0 774-0 



3-3 2-8 



2 -2 



9 -9 



9 -9 



776-1 778-5 776-4 770-5 777-0 

 at 14-7 atl2-7 at!2-5 at 14-5 at 17-3 



To reduce the values in English measure to metres and the Centi- 

 grade scale, I have simply taken the reducing factor 1-8 X -304794, 

 although the barometer on the two systems is not exactly the same: 

 for this is taken into account in the comparison of the thermometers. 

 However, a barometer at 30 in. and 60 F. is equivalent to 759-86 mm. 

 at C. which hardly makes a difference of 0-01 C. in the temperature 

 of the hundred-degree point. 



In combining these so as to get at the true difference of Joule's and 

 my result, we must give these different determinations weights accord- 

 ing to their respective accuracy, especially as some of the results, as 

 No. 11, have very little weight. Joule rejected quite a number of his 

 results, but I have thought it best to include them, giving them small 

 weights, however. In this way we obtain a value for Joule's experiment 



