78 HEAT. 



to say that the heat was supplied to water in a calorimeter by violent 

 stirring, the energy put in by the stirring being transformed to heat 

 proportional to the work done. Rowland found that the same amount 

 of work produced a different temperature rise in the same quantity of 

 water at different parts of the scale. The range was from 5 to 36 C., 

 and there was distinct evidence for the existence of a minimum specific 

 heat about 30. The recalculated results are represented in Fig. 60. 

 Rowland verified the variation by experiments by the method of mixtures, 

 from which he found the coefficient of decrease between to 30 to be 

 000236. 



In 1893 a most careful determination of the variation between 

 15 and 25 was published by Griffiths,* who used the method of electric 

 heating. The research was really on the mechanical equivalent of heat, 

 but we may regard it here as one on the specific heat of water. 



Taking the specific heat at 15 as 1, Griffiths found that if t lies 

 between 15 and 25 then 



Specific heat at t = I - -000266( - 15) 



where t is the temperature on the hydrogen scale. This is represented 

 in Fig. 60. 



In 1894f some experiments on the latent heat of steam led 

 Griffiths to suppose that the mean specific heat of water between 

 and 100 is exceedingly near to that at 15. Since the specific heat is 

 decreasing at 15, this implies, of course, that it must reach a mini- 

 mum before 100, and then increase again. Griffiths' supposition was 

 confirmed by Dr. Joly by an experiment with his steam calorimeter, in 

 which a known weight of water was raised from about 12 to 100. so 

 that its mean specific heat between 12 and 100" was determined. 

 Griffiths found from Joly's work that 



Mean specific 



Specific heat at 15 



instead of - =1'004 as found by Regnault. 



1*0008 



Meanwhile Bartoli and Stracciati | had been carrying out a very 

 extensive series of researches on the specific heat of water by the 

 method of mixtures. They made three sets of experiments. In all 

 the calorimeter contained a known weight of water initially at the 

 temperature of the surroundings. In the first set, different metals of 

 specific heat known through the range used were heated to 100 and 

 dropped into the calorimeter. In the second set, a known weight of 

 water at was dropped in ; and in the third set, a known weight of 

 water at a temperature above that of the calorimeter was mixed. The 

 three sets showed results very much of the same nature. The mean 

 is shown in Fig. 60. It should be noted that the metal set gave a 



* Phil. Tram., 1893, A., p. 361. 



t Phil. Trans., 1895, A., p. 320. Dr. Joly's experiment referred to in the text ia 

 described in the paper. 



J i\uovo Cimento, 32. A brief account is given in Beiblatter, xvii., 1893, pp. 

 542, 638, 1038. 



