Parts of Water and of Dephlogifiicated Air, 355 
and phofphorus, and the alkali and earth in charcoal, may at- 
tract the pklogifton fo powerfully that the heat they contain 
may not be able to overcome the adhefion of their particles, 
until, by the effect of external heat, they are once removed te 
fuch a diftance from one another as to be out of the {phere of 
that kind of attraction *. . | 
If it be found to be a conftant fact, that equal additions of 
phlogifton to dephlogifticated air do not extricate equal quan- 
tities of heat, that may afford the means of finding the quanti- 
ties of heat contained in phlogifton and dephlogifticated air re- 
fpectively, and folve the problem. . 
. Many other ideas on thefe fubjects ete themfelves; but 
J am not bold enough to trouble you, or the public, with any 
{peculations, but fuch as I think are fupported. by uncontro- 
verted facts. | 
I muft therefore bring this long letter to a conclufion, and 
leave to others the future profecution of a fubje&t which, how- 
ever engaging, my neceffary avocations prevent me from pur- 
fuing. I cannot however conclude, without acknowledging my 
obligations to Dr. PRIESTLEY, who has given me every infor- 
mation and affiftance in his power, in the courfe of my enqui- 
ties, with that candour and liberality of fenti iment which diftin- 
guith his charaéter. 
I return you my thanks for the obliging attention you have 
paid to this hypothefis; and remain, with much efteem, &c, 
JAMES WATT. 
* On the whole, this queftion feems to involve fo many difficulties, that it cannot 
_ be cleared up without many new experiments. 
Awe 
Vor, LXXIV. Aaa 
