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 — ta- 
king place, or whether the temperature were stationary. 
As these experiments were made for a purpose purely eaniaibe 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 
Petit} (as well as of many other philosophers,) have left little to be 
desired in regard: to the rate of costing’ in vacuo, and in a limited que 
tity of gas. 
They have separated these two things, and given the indocncenl 
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? 
ae or less velocities of the currents materially influence 
the proportion of heat which will be abstracted by a given extent of 
surface, when the venrny itself depends on an excess of — 
in the moving fluid ? ste 
Even allowing for these circumstances, will the quantity of heat 
abstracted bear any constant ratio to the excess above the tempera- 
iure of the room, with which the gas first enters from the chimney ? 
The table is intended to furnish some data for napeerering St in- 
, eas 
se oa 
* Tt will be understood that the remarks in the eighth column, pes to the por- 
ti results contained in the sixth, and not to the more general a an which 
may chance to fall on the same | lines in the seventh. 
{See Ann, de Chim. et de Phys. Vol. vii, pp. 113, 225 and 337. 
