1830 .] 
by Messrs. Dulong and Petit. 
281 
given body, in cooling to a certain temperature— for such a scale would be founded 
on the assumption, that the capacities are constant ; or at least that they increase 
according to tbe same law in all bodies. Now both these assumptions are equally 
false. We have given, in the following table, the temperatures which would be 
obtained in this way, in employing each of the different substances included in the 
preceding table. We assume that they have been all subjected to the heat of a 
liquid kept at a temperature of 300°, as indicated by an air thermometer. 
Iron, 
332,2 
Silver, 
329,3 
Zinc, 
.328,5 
Antimony, 
324,8 
Glass, 
322,1 
Copper, 
320,0 
Mercury, 
318,2 
Flatiua, 
317,9 
General Reflections and Conclusions. 
Now, that we have shown, by experiment, within sufficiently wide limits, the laws 
of those phenomena, which may be employed in the measure of temperature, we 
have it in our power to decide whether tbe thermometric scale proposed by Mr. 
Dalton, possesses really all tbe advantages he attributes to it. in measuring tem- 
peratures on this scale, we shall find, according to this philosopher: — 
l mo. That the expansion of mercury and other liquids is proportional to the 
squares of the temperatures — reckoning from the point of greatest density in each. 
2do. That gases expand in geometrical proportion, to temperatures increasing 
arithmetically. 
3to. That reducing to the same volume, the capacities of all bodies are the same. 
4to. And lastly, that in the cooling of bodies, the temperatures form a geome- 
trical series, when the times are taken as an arithmetical one. 
The manner in which Mr. Dalton has brought forward the principle on which 
he founds the construction of his scale, sufficiently indicates, that it can only be 
considered as a hypothesis, with the supposed advantage of connecting together a 
number of phenomena by very simple relations. Such advantage, if it really ex- 
isted, would be important enough to induce our adoption of so happy an idea- 
even though it should fail to be established by direct experiment. We shall not, 
therefore, stop to discuss the value of the particular observations which appear to 
have influenced this celebrated philosopher (physicien), but confine ourselves to 
the examination, whether the results established in this memoir agree with the laws 
in question. 
Iu the comparison we are about to make, we shall consider the air thermometer 
(the degiees of which are all equal to the 100th part of the difference between the 
freezing and boiling points,) as an arbitrary scale ; and without troubling ourselves, 
as to the actual quantities of heat which may he represented by the indications of 
this instrument — we shall use it merely as a common measure to pass from one 
scale to another. 
Instead of enquiring whether, in measuring temperatures by Mr. Dalton’s ther- 
mometer, the expansion of mercury and of air would really follow the laws he has 
pointed out, it will be more simple to calculate the indications which would corres- 
pond on his scale, with the observed expansions of each of these substances, (taking 
for granted that his laws are correct,) and then compare the results obtained for 
each. The following table exhibits the agreement found between some of these 
terms, calculated in this manner. 
Teinperatures,as derived 
from an air thermome- 
ter, with uniform scale. 
Corresponding temperatures, 
as they would be indicated 
by a mercurial thermometer, 
ou Mr. Dalton’s hypothesis. 
Corresponding temperatures 
as they would he indicated 
by au air thermometer, ou 
Mr. Dalton’s hypothesis. 
— 40° 
— 114°, 8 
— 52°, 2 
0 
0 
0 
50 
57 ,4 
63 ,9 
100 
100 
100 , 
2(10 
169 ,1 
175 ,7 
300 
226 ,7 
236 ,8 
350 
251 ,1 
263 ,2 
L 
