and the Mode of its Communication. 155 
that the heat which it acquires is not communicated to it by the 
flame, but by the wood to which it adheres, which is soon heated 
by the flame, and even set on fire. 
I cannot refrain from just observing, that it appears to me to 
be extremely difficult to reconcile the results of any of the fore- 
going experiments, with the hypothesis of modern chemists re- 
specting the materiality of heat. 
Deeply sensible of the insufficiency of the powers of the 
human mind, to unfold the mysteries of nature, and discover 
the agents she employs, and their mode of action, in her secret 
and invisible operations ; and being moreover fully aware of the 
danger of forming an attachment to a false theory, and of the 
folly of wasting time in idle speculations ; I have ever, in my phi- 
losophical researches, been much more anxious to discover new 
facts, and to show how the discoveries of others may be made 
useful to mankind, than to invent plausible theories; which much 
oftener tend to misguide, than to lead us in the path of truth 
and science. 
There are however situations, in which an experimental en- 
quirer sometimes finds himself, where it is almost impossible for 
him to abstain from forming, or adopting, some general theory, 
for the purpose of explaining the phenomena which fall under 
his observation, and directing him in his future researches. 
Finding myself in that situation at this time, I beg the atten- 
tion, and above all the indulgence , of the Society, while I en- 
deavour to explain the conjectures I have formed, respecting 
the nature of heat, and the mode of its communication. 
Hot and cold , like fast and slow , are mere relative terms ; 
and, as there is no relation, or proportion, between motion and 
a state of rest, so there can be no relation between any degree 
X 2 
