1819.] and onthe Laws of the Communication of Heat. 113 
precision. But we cannot hope to discover the most general 
properties; or, if the expression is preferred, the most simple 
laws of heat, till we have compared thermometers constructed 
with substances taken from the three general states in which 
matter exists, and till we have calculated the corresponding 
quantities of heat. 
Though this subject of research must naturally have presented 
itself to the,mind of every philosopher, we must acknowledge 
that it has not yet been treated in a manner suitable to its 
importance. ‘The essays of Deluc and Crawford embrace too 
small a portion of the thermometric scale to enable us to deduce 
general consequences from them. Indeed this is a reproach 
which applies to almost all the experiments relative to the theory 
of heat ; and it has become the source of.a great number of 
erroneous inductions. Indeed it is easy to conceive that pheno- 
mena subjected to very different laws may appear identical 
within a certain interval of temperature, and that if we remain 
satisfied with observing them within those limits in which their 
divergence is almost insensible, we shall be led to ascribe their 
feeble discordance to errors of observation, and shall be destitute 
of the data requisite to mount to their real cause. We shall have 
occasion several times in the course of this memoir to show the 
justice of this reflection. 
Mr. Dalton, considering this question from a point of view 
much more elevated, has endeavoured to establish general laws 
applicable to the measurement of all temperatures. These laws, 
it must be acknowledged, form an imposing whole, by their 
regularity and simplicity. Unfortunately this skilful philosopher 
proceeded with too much rapidity to generalize his very ingenious 
notions ; but which depended upon uncertain data. The conse- 
quence is, that there is scarcely one of his assertions but what is 
contradicted by the result of the researches which we are now 
going to make known. 
These researches have for their principal object the laws of 
the cooling of bodies, plunged into an elastic fluid of any nature 
whatever, and at different densities and temperatures. Before 
studying this class of phenomena, it was indispensable to obtain 
more exact ideas than we at present possess respecting the 
measure of elevated temperatures. It was by the examination 
of this accessory, but highly interesting question, that we began 
our labours. e shall hkewise begin our memoir with it. 
This memoir then will consist of two very distinct parts. The 
first will have for its object every thing which relates to the 
measure of temperature ; the second will contain the general 
Jaws of cooling. 
Part I.—Of the Measure of Temperatures. 
If there existed a body whose dilatations were subjected to a 
law, so simple and so regular that successive additions of equal 
Vou. XIII. N° II. H 
