332 Economy of Fuel. 



the rate of variation. The remarks* on this subject are probably 

 sufficiently numerous to enable us to judge even in those cases in 

 which the variation was not noted, what was the actual change ta- 

 king place, or whether the temperature were stationary. 



As these experiments were made for a purpose purely practical, it 

 was no part of their aim to determine the abstract laws relating to 

 the rate of cooling. Nor is that, probably, necessary in the present 

 state of science. The very elaborate experiments of Dulong and 

 Petitf (as well as of many other philosophers,) have left little to be 

 desired in regard to the rate of cooling in vacuo, and in a limited quan- 

 tity of gas. 



They have separated these two things, and given the influence of 

 each circumstance a distinct consideration. But in what manner 

 will those laws which have been deduced, be modified by the cur- 

 rents of gas traversing the trunks of chimnies or the pipes of stoves im 

 Will the greater or less velocities of the currents materially influence 

 the proportion of heat which will be abstracted by a given extent of 

 surface, when the velocity itself depends on an excess of temperature 

 in the moving fluid ? 



Even allowing for these circumstances, will the quantity of heat 

 abstracted bear any constant ratio to the excess above the tempera- 

 ture of the room, with which the gas first enters from the chimney ? 

 The table is intended to furnish some data for answering these in- 

 quiries. 



* It will be understood that the remarks in the eighth column, refer to the par- 

 ticular results contained in the sixth, and not to the more general averages which 

 may chance to fall on the same lines in the seventh. 



1 See Ann. de Chim. et de Phys. Vol. vi.i, pp. 113, 225 and 337. 



