44 



PROCEEDINGS OF THE AMERICAN ACADEMY 



772.7 774.6 773.1 767.0 774.0 



Joule's values 



Correction for thermometer 

 " " capacity 

 " . " latitude 

 " to vacuum 



Corrected values 



To reduce the values in English measure to meters 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 0° C. which hardly makes a difference of 0°.01 C. in the tempera 

 ture 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 

 according 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 of 426.75 at 14°. 6, my value at this point 

 being 427.52. The difference amounts to 1 in 550 only. Giving 

 the observations equal weights, this would have been 1 in 480 nearly. 

 The quantity 426.75 is what I find at 18° C. So that my result 

 at this particular temperature differs from that of Joule only the 

 amount that water changes in speciQc heat in 3°.4 C. 



