Intelligence and Miscellaneous Articles, 143 



of 3 or 4 degrees is produced ; this is noted, after which the cooling 

 of the thermometer is observed during five minutes. The quantity 

 of heat given off is known, the effect it has produced is calculated, 

 and from the known formulae of calorimetry the desired capacity is 

 deduced*. 



The old method required two operations, which were : — the first, 

 to heat in a stove for a long time the body to be studied, and to pour 

 it with minute precautions into the calorimeter ; the second, to ob- 

 serve the thermometer immersed in the calorimeter. In the method 

 which I propose the first operation is omitted, and the second suffices 

 such as it was before. The corrections remain the same, but are 

 simplified. 



They are simplified because a lower temperature is sufficient, and 

 because, the heat given off being proportional to the time, the me- 

 thod known as Rumford's is applicable. We may even dispense 

 with all correction, as I shall show. 



I provided the external envelope of the apparatus with a spiral 

 twenty times as long as the first, and immersed the whole into a 

 vessel containing twenty times as much liquid as the calorimeter, 

 and forming a medium in which the latter is immersed. The 

 current passes simultaneously into the two spirals ; it produces 

 there heats proportional to the quantities of liquid, and consequently 

 equal heatings. At each moment the temperatures of the calorimeter 

 and its surroundings are in equilibrium, and the first, neither gaining 

 nor losing any thing by radiation, is subject only to the action of the 

 current. It is impossible to maintain this equilibrium strictly during 

 the whole time of the experiments if they are prolonged ; but it is 

 very easy to establish it within a few tenths ; and that is sufficient to 

 obviate all necessity for correction. Thus we can measure for each 

 degree the specific heat of a liquid (water or alcohol for example) 

 from the lowest temperatures to its boiling-point. 



I have verified this method by determining the capacities of iron 

 and of copper, which are the most difficult to obtain exactly, because 

 they are very small. I found 0*098, 0*093. M. Regnault obtained 

 the numbers 0-113, 0'095, which are a little larger ; but he operated 

 with a higher temperature. 



II. Of Gases and Vapours. — The advantages of this method are 

 especially apparent when treating of aeriform fluids. A gaseous cur- 

 rent passes through a glass tube to the middle of a cork of badly 

 conducting material ; a thermometer there measures its tempera- 

 ture. It immediately enters a second tube through the folds of a 

 metal spiral or a bundle of twisted wires traversed by electricity — 

 that is to say, through a focus ; it becomes heated and meets a second 

 thermometer, which measures its increase of temperature. Before 



* Suppose two experiments to be made with the same current during the 

 same time, with the weights P and P' of water and of the liquid to be stu- 

 died. The quantities of heat are the same; they have heated the liquids 

 6 and 6' degrees. Denoting the weight of the calorimeter reduced to water 

 by 7T, and the capacity sought by x, we have 



(P + 7r)0=(P'a? + 7r)0'. 



