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SECOND REPORT— 1882 . 
posed ; and the changes which cultivation and other circum¬ 
stances may gradually effect in the elements of climate, espe¬ 
cially with regard to the isotherai * and isocheimal f lines, even 
when the mean annual temperature suffers little variation. The 
author next considers, at some length, the particular influence 
of the configuration of soil in modifying the climate, contrasts 
the continental arrangements of the two hemispheres, and the 
characters of a terrestrial and marine climate at the equator. 
He points out in a clear manner the influence of forests upon 
temperature, from the shadow they produce, from the coolness 
created by the evaporation at their surfaces, and from the ex¬ 
tended radiating surface which they present. Such are the 
principally interesting points to which this Essay alludes. In 
the same volume, Baron Humboldt gives some views upon the cli¬ 
mate of Asia, which he has collected during his late journey. 
The subject of the decrease of heat as w r e ascend above the 
surface of the earth, has excited, and especially in Britain, 
much less attention than it deserves. We hardly know a finer 
problem for complete solution in Meteorology. Little has been 
done towards it during the last few years, but we cannot pass 
it over quite without notice. The principle upon which this 
diminution of temperature takes places in the higher regions of 
the atmosphere, is now universally allowed to be the increased 
capacity for caloric of air when it is rarified. The first ques¬ 
tion for solution is, therefore, the specific heat of air under dif¬ 
ferent degrees of condensation,—a point of by no means easy 
investigation, and which has engaged the attention of some of 
the first philosophers of the day, as we have already noticed. 
It has been investigated experimentally by Dalton and Leslie, 
De la Rive and Marcet; and theoretically by Laplace, Ivory, 
Poisson, and Avogadro. The object is the more important, 
as it is intimately connected with the amount of astronomical 
refractions. We do not consider, however, that the total effect 
can be expressed simply by the law of specific heats varying 
with height; and it appears that the experimental data which 
have been sought by observations on the atmosphere, have not 
generally been conducted on principles which can lead to con¬ 
clusive results. I do not allude merely to the use of insulated 
observations of temperature at great elevations, which in my 
opinion can lead to no general result X, because of the innumera¬ 
ble accidental causes always at work, which can only have 
their influence multiplied by a long series of observations,—but 
to the fact, that observations of temperatures at great heights, 
* Equal summer temperature. f Equal winter temperature. 
X Such as the collection of insulated observations in Ramond Surla Formule 
Barometrique de la Mecanique Celeste, p. 189. 
