OP ARTS AND SCIENCES. 



135 



c, draw a line, j c, parallel to dm, and where it meets Icj will be the 

 required point, and will give the value of 6". Hence, the rise of tem- 

 perature, corrected for all errors, will be kj. 



This method, of course, only applies to cases where the final tem- 

 perature of the calorimeter is greater than that of the air ; otherwise 

 there will be no maximum. 



In practice, the line dm is not straight, but becomes more and more 

 nearly parallel to the base line. This is partly due to the constant 

 decrease of the difference of temperature between the calorimeter and 

 the air, but is too great for that to account for it. I have traced it to 

 the thin metal jacket surrounding the calorimeter, and I must con- 

 demn, in the strongest possible manner, all such arrangements of calo- 

 rimeters as have such a thin metal jacket around them. The jacket is 



of an uncertain temperature, between that of the calorimeter and the 

 air. "When the calorimeter changes in temperature, the jacket follows 

 it, but only after some time ; hence, the heat lost in radiation is uncer- 

 tain. The true method is to have a water jacket of constant tempera- 

 ture, and then the rate of decrease of temperature will be nearly 

 constant for a long time. 



The following results have been obtained by Mr. Jacques, Fellow 

 of the University, though the first was obtained by myself. Correc- 

 tions were, of course, made for the amount of thermometer stem in 

 the air. 



Mean Specific Heat. 



.0915 

 .0915 

 .0896 

 .0895 

 .0885 

 .0910 



