os 
178 Dulong and Petit on the Measure of Temperatures, [Marcu, 
It is because they did not follow this plan that Messrs. Dalton 
and Leslie have obtained such inaccurate results respecting this 
question. ‘The first, led away without doubt by the notion that 
the law of Richmann is verified in his thermometric scale, and 
not having compared the cooling of different surfaces for a suffi- 
ciently large interval, had been led to suppose that the law of 
cooling is the same in all bodies. And Mr. Leslie, who had 
remarked that the law changes with the nature of the surface, 
not having included in his experiments temperatures sufficiently 
high, concluded, that the difference which he observed always 
increases as we advance in the thermometric scale. This has 
led him to consequences very far from the truth, respecting 
which we shall have ‘occasion to make observations in the sequel. 
Weshall merely remark, in expressing our surprise, that Mr. Leslie, 
whom the influence of the nature of the body on the law of 
cooling did not escape, and who had concluded in consequence 
that the law of Richmann must be inaccurate, has nevertheless 
made use of this in most of his experiments. 
We terminated these preliminary researches by examining th 
€ooling of water in three vessels of tin plate of the same size ; 
the first spherical ; the second cylindrical, having a height equal 
to twice the diameter of its base ; and the third likewise cylin- 
drical, but having a height equal to halfits diameter. 
Excesses of Velocity of Ditto of the|Ditto of the|Ratioofcolumi) Ratioofcolumn 
tempera- cooling ofjfirst  ylin- second cy-/three tocolumn|four-to column 
ture. jthe sphere. |der. linder. two. two. 
60° 0:90 1-11 1:01 1-23 1:12 
50 0°73 0-89 0-80 1:22 1-10 
40 0-54 0-66 0°60 1-22 ing 1 
30 0°38 0°47 0°43 1-23 1:13 
20 0-21 0:26 0-23 1-24 1:10 
The law of cooling is still the same for the three vessels of 
different shapes, as appears by the ratios contained in the last 
two columns. The form of the vessel then has no influence on 
the law of cooling ; and this assertion is confirmed by this, that 
the ratios found between the velocities of cooling are nearly the 
same as those that exist between the surfaces of the vessels, as 
may be easily ascertained. On recapitulating the results which 
we have just made known, we see that the law of cooling of a 
liquid mass, though it varies with the enveloping surface, is 
nevertheless independent of the nature of the liquid, and of the 
form and size of the vessel which contains it. This was the point 
which we proposed to establish in this introduction, and which 
constituted the basis of the researches which we are now going 
to explain. 
