440 On the Determination of the [Dec. 



the same process as that which pave us the maximum temperature 

 to which the current of hot gas brought the calorimeter. We made 

 vapour pass through the tube, D E, (fig. 5) without any current of 

 gas, and observed the rate at which the calorimeter heated. We 

 stopped the experiment when the increase of heat in the calori. 

 meter was become exceedingly slow. Then we raised the heat of 

 the calorimeter artificially about 2 degrees, thus raising it above the 

 maximum point, and continued the experiment till it had almost 

 eeased to sink. We took the mean between these two terms as the 

 effect produced by the vapour tube. This experiment was made 

 twice with great care. In the first experiment the ascending series 

 conducted us to 51-8° (the air being at 46-778°), and the descend- 

 ing series to 53-042° (the air being at 46-634°). If we take the 

 mean between these two numbers, we get 5*58° for the maximum 

 effect produced by the vapour tube on the calorimeter. The 

 second experiment gave us exactly the same number. 



It may be asked, if the steam tube will communicate as much 

 heat to the calorimeter when the steam of gas is passing as when it 

 is absent. It is easy to see that it will not, since the temperature 

 of the tube, D E, remaining the same, the calorimeter is hotter in 

 the one case than in the other ; and it is a well-known principle, 

 that when one body communicates heat to another, the quantity 

 communicated is the more the greater the difference of temperature 

 between the two bodies. 



It is very difficult in the present case to determine how much the 

 heat communicated by the steam tube will be diminished by the 

 increase of temperature of the calorimeter. Fortunately, the 

 quantity is so small that it is of little importance. We may sup- 

 pose, without risking any error of importance, that the quantity of 

 heat yielded is as the difference between the temperature of the 

 calorimeter and of the tube, D E. This difference being 144° in 

 the experiments which we have related, and producing an elevation 

 of temperature amounting to 5\58° in the calorimeter, this elevation 

 ought to be 4-5°, when the difference between the temperature of 

 the steam tube, D E, and of the calorimeter, is only 129-6°, as 

 was the case in the experiments which we made on the different 

 gases. 



Note 2d. 



We determined in the following manner at what degree the cur- 

 rent of hot air maintained the calorimeter stationary. 



In consequence of data furnished by a preliminary experiment, 

 we raised the temperature of the calorimeter to 76 359°. The 

 thermometer, indicating the temperature of the air of the room, 

 stood at 44-83°. 



The calorimeter was then wiped with care, that no unknown 

 cause might accelerate its cooling, and the current of hot gas was 

 made to pass through it. The experiment was continued till the 

 thermometer of the calorimeter, observed every ten minutes, almost 

 ceased to rise. The observations were as follows : — 



