117 
of Edinburgh, Session 1872 - 73 . 
observations ; and I may remark in passing, what applies to all, 
that allowance must be made throughout for some factor of specific 
heat. The results were as follows : — The seasonal and monthly 
means in the tree and in the air were not sensibly different. The 
variations in the tree, in M. Becquerel’s own observations, appear 
as considerably less than a fourth of those in the atmosphere, and 
he has calculated, from observations made at Geneva between 1796 
and 1798, that the variations in the tree were less than a fifth of 
those in the air ; but the tree in this case, besides being of a 
different species, was seven or eight inches thicker than the one 
experimented on by himself.* The variations in the tree, therefore, 
are always less than those in the air, the ratio between the two 
depending apparently on the thickness of the tree in question and 
the rapidity with which the variations followed upon one another. 
The times of the maxima, moreover, were widely different : in the 
air, the maximum occurs at 2 p.m. in winter, and at 3 p.m. in 
summer; in the tree, it occurs in winter at 6 p.m., and in summer 
between 10 and 11 p.m. At nine in the morning in the month of 
June, the temperatures of the tree and of the air had come to an 
equilibrium. A similar difference of progression is visible in the 
means, which differ most in spring and autumn, and tend to 
equalise themselves in winter and in summer. But it appears 
most strikingly in the case of variations somewhat longer in period 
than the daily ranges. The following temperatures occurred 
during M. Becquerel’s observations in the Jardin des Plantes: — 
1859. 
rv . Temperature Temperature 
of the Air. in the Tree. 
O O 
Dec 
.15, 
26-78 
32 
?> 
16, 
19.76 
32 
„ 
17, 
17-78 
31-46 
„ 
18, 
13-28 
' 30-56 
55 
19, 
12-02 
28-40 
„ 
20, 
12-54 
25-34 
55 
21, 
38-30 
27-86 
55 
22, 
43-34 
30-92 
55 
23, 
44-06 
31-46 
* Atlas Meteorologique de l’Observatoire Imperial, 1867. 
