GLEANINGS 
IN 
SCIENCE. 
JYo. 2 February , 1829 . 
I . — On the Measure of Temperature, and the Lairs which regulate the 
Communication of Heat*. By MM. Dulong and Petit. 
[From the w Journal de L'Ecole Royale Poly technique, T. XI.] 
Introductory Observations. 
Ftlom the earliest cultivation of experimental physics, it has been generally 
admitted, that amongst all the effects of heat, we ought to adopt change of volume 
as preferable to every other class of phenomena due to that cause, in our attempts 
to measure its mod ideations, whether natural or artificial. Still there was a wide 
interval between this general conviction, and that knowledge of the subject 
required in constructing thermometers on just principles ; such in fact as should 
render them comparable one with the other. Rut the frequent employment of 
these instruments, and the value of the data which they furnish, having continued 
to attract attention to the subject, and to those circumstances which might in any 
way affect their indications, all the particulars of their construction have been 
studied with so much care, and in such detail, as to leave little to be wished for on 
this head. 
It was, in fact, indispensable to use the greatest accuracy in thermometrical obser- 
vation ; but it did not follow, that such accuracy would lead us to a full knowledge 
of the theory of heat. For we may refer the varying phenomena to an arbitrary 
scale of temperature, and then investigate empirical formula, which will exactly 
represent observation ; but we could not hope to discover general properties, or 
what may be called the most simple laws of heat, without comparing thermo- 
meters constructed with substances in each of the three different states, of which 
matter is susceptible, and de termini tig the relations which exist between the indi- 
cations of these instruments, and the quantities of heat added or subtracted, to pro- 
duce determinate changes of temperature. 
Although this subject of research must have suggested itself to the mind of 
every inquirer, it must be allowed, that it has not yet been followed out with all 
the care, and in that fulness which its importance demands. The labours of 
* This truly valuable paper was crowned by the Academy of Sciences in its sitting 
of the 16th .March 1818, and the prize in physics decreed to the very ingenious and 
profound authors. 
It has been noticed with high commendation in all our receut works in which the 
subject is treated of; but in so imperfect a manner, that the true value of the results 
cannot be collected. It appeared, therefore, desirable to give a more complete idea 
of its coutents thau has yet been done ; and it was at first supposed, that a tolerably 
clear abstract might be made of it. On making the attempt, it was found, that the 
authors had been any thing hut prolix, and that without sacrificing clearness it 
could not he shortened. As however, the paper us too long for our limits, we are 
compelled to divide it into different portions; and this is easily done, ns the Essay 
itself, embracing different topics, allows a subdivision without any break of connec- 
tion. It is divided into two parts; the 1st treats of the measure of temperature ; 
the 2d of tne laws of cooling. The first part again is subdivided into the follow- 
ing sections : 
1. — On the expansion of the gases. 
2 — On the expansion of mercury. 
3 — On the expansion of solids. 
4. — On the specific heat^f bodies. 
The present Number contains & 1 . — Ed. 
