1831.] 
On the Measure of Temperature, fyc. 
363 
The foregoing remarks have been offered, in the hopes of giving some general 
idea of the objects which may be attended to in making geological observations, or 
which are included in the extensive scofie of matter which geology embrace* 
within its researches. To recur, however, to what is the chief object, namely, to 
collect data for giving a geological and mineralogical map, sections and descrip- 
tions of the country, the manner in which specimens are to be taken, and the 
direction and dimensions of the beds marked for this purpose, has been specified in 
the first pages. The labels on the specimens must be securely affixed, and the 
reference to their position in the plan carefully marked, to avoid the chance of 
error. The geological plans should be coloured, distinguishing the different rocks, 
as they are traced on the surface, and in the section. To induce uniformity 
in this respect, a table of colours is given for the principal rocks, which is nearly 
the same as that in the Geological Map of England. It has been found convenient, 
in addition to the colours, to have letters of reference, as is shown in the sketch : 
any remarks, as of simple minerals found in the beds, can be made to the same 
letters. 
II On the Measure of Temperature , and on the Laws which regulate 
the Communication of Heat. By M. M. Dulong and Petit. 
[From the Journal Polytechnique, T. IX.] 
§ 4. On Cooling in Air and in the Gases. 
The laws of cooling in vacuo being known, it is easy enough to separate from the 
total cooling of a body, surrounded by air or any other gas, the portion of the effect 
due to the contact of the fluid. It is sufficient evidently to deduct from the actual 
rate of cooling that which would be found, if (all else being equal) the body had 
been placed in vacuo . This correction can always be made, now that we have a 
formula to represent this rate with every degree of accuracy, and for every possible 
case. We can then determine the energy of the cooling process as due solely to 
the contact of fluids, and such as they would be observed could we deprive sub- 
stances of the power of radiation. This part of our enquiry required a great many 
experiments to be made, since the laws which we were desirous of investigating 
were to lie studied with different gases, and with each of these again tor different 
nressures and temperatures. Each experiment has been conducted, and the result 
calculated in the manner previously explained : we shall therefore confine ourselves 
to eivinir the mean results of calculation from all these observations. 
The first Question which it was incumbent to enquire into was, Whether the sur- 
(JJnf the bodv which so powerfully affects radiation, would effect any change m 
rte loss SJasiooea by tbe contact of fluids ? To determine this point, ,t was 
sufficient to observe the cooling of our thermometer m a gas of a determinate 
elasticity and temperature, first with the natural surface of the glass, and afterwards 
88 Of alHhe^exp^i^^s which we made with this question in view, we shall here 
^?nS“e f 1wvfdtto cooling of the largo thermometer in tbe balloon, 
co^tog ah of the density ,72 metres', and of the temperature 20°, . 
First Case. 
The Thermometer with its natural surface. 
r ~ 
Excess of temp, 
of the thermo- 
meter. 
Total rate of cool- 
ing of the ther- 
mometer. 
Rate of cool 
ing in va- 
cuo. 
Dift’erence,or rate 
of cooling due 
to the air. 
200® 
180 
160 
140 
120 
100 
14°, 04 
11 ,76 
9 ,85 
8 ,05 
6 ,46 
4 ,99 
8°, 5 6 
7 ,01 
5 ,68 
4 ,54 
3 ,56 
2 ,72 
5°, 48 
4 ,75 
4 ,17 
3 ,51 
2 ,90 
2 ,27 
