Ox THE MECHANICAL EQUIVALENT OF HEAT 443 



stopped and a radiation experiment begun. The last operation was to 

 weigh the calorimeter again, after removing the thermometer and safety 

 tube, and also the weights which had been used. 



The chronograph sheet, having then been removed from the cylin- 

 der, had the time records identified and marked, as well as the ther- 

 mometer records. Each line of the chronograph record was then num- 

 bered arbitrarily, and a table made indicating the stand of the ther- 

 mometer and the number of the revolutions and fractions of a revolu- 

 tion as recorded on the chronograph sheet. The times at which these 

 temperatures were reached was also found by interpolation, and re- 

 corded in another column. 



From the column of times the readings of the torsion circle could be 

 identified, and so all the necessary data would be at hand for calculating 

 the work required to raise the temperature of one kilogramme of the 

 water from the first recorded temperature to any succeeding tempera- 

 ture. 



As these temperatures usually contained fractions, the amount of 

 work necessary to raise one kilogramme of the water to the even degrees 

 could then be found from this table by interpolation. Joule's equiva- 

 lent at any point would then be merely the difference of any two suc- 

 ceeding numbers; or, better, one tenth the difference of two numbers 

 situated 10 apart, or, in general, the difference of the numbers divided 

 by the difference of the temperatures. 



It would be a perfectly simple matter to make the record of the tor- 

 sion circle entirely automatic, and I think I shall modify the apparatus 

 in that manner in the future. 



It would take too much space to give the details of each experiment; 

 but, to show the process of calculation, I will give the experiment of 

 Dec. 17, 1878, as a specimen. The chronograph sheet, of course, I 

 cannot give. The computation is at first in gravitation measure, but 

 afterwards reduced to absolute measure. 



The calorimeter before the experiment weighed 12-2733 kil. 

 The calorimeter after the experiment weighed 12-2716 kil. 



Mean 12-2720 kil. 

 Weight of calorimeter alone 3-8721 kil. 



. . Water alone weighed 8-3999 kil. 



3470 kil. 



Total capacity 8-7469 kil. 



