SUPPLEMENTARY REPORT ON METEOROLOGY. 59 
that direction. Besides, the atmosphere is no doubt a medium 
of that description, which permits solar radiation to pass much 
more freely than heat which has combined with the materials of 
the globe at a low temperature; hence the surface of the globe 
may be considered as a true accumulating source of heat, the 
further we recede from which the greater will be the cold*. 
57. A just apprehension of these circumstances will serve to 
explain the modifications of this phanomenon, as well as the 
phenomenon itself. This I have lately endeavoured to do, and 
to show the accordance of the theory with factst. It is known, 
from experiment, that the decrement of temperature is most 
rapid in spring, and least so in autumn. This appears, both 
from the reduced observations on the Pentland Hills, near 
Edinburgh, alluded to in my last Report (p. 219), and from 
those on a great scale, conducted so long at Geneva and the 
Great St. Bernard{. I have shown that this arises from the 
following peculiarities of the annual curves at two stations at 
different elevations; (1.) the curve at the upper or colder station 
stands wholly below that at the warmer one. Hence were these 
two curves similar, and their epochs the same, the difference 
would be constant. But (2.) the range at the upper station is 
less than that at the lower one; hence the summer difference of 
temperatures is on the whole greater than the winter difference, 
which we know to be the fact§. (3.) The maxima above occur 
later than those below, so that the whole colder and flatter 
curve is shifted to the right hand, and hence the epoch of 
maximum difference precedes the epoch of maximum tempera- 
ture, according to a law which I have investigated in the paper 
referred to. 
58. The diurnal curves correspond to the annual curves in 
the two first particulars, but not in the last. I have attempted 
to explain the cause of this difference, and to show that, in 
point of fact, the epoch of the diurnal curve at the higher 
station is (up to a certain height at least) accelerated upon the 
lower one instead of the reverse, and that consequently a re- 
tardation of the maximum difference upon the maximum tem- 
perature occurs, which is really the case||.. A clear apprehen- 
sion of the progress of temperature in the atmosphere and 
* See on this subject Fourier, Mém. de l’ Académie des Sciences, tom. vii.; 
Ann, de Chim. xxvii. 155 ; Saussure, Voyages dans les Alpes, 4to, tom. ii. § 932, 
&e.; Kamtz, Lehrbuch, ii. 128; Pouillet, Comptes Rendus, vii. 49. 
{+ Edinburgh Transactions, xiv. 489 (1840); and Jameson’s Journal, 
October 1840. 
{ Dove’s Repertorium, iii. 337. 
§ See First Report, p. 219. Kamtz, Lehrbuch, ii. 140. 
|| Saussure, Voyages, iv. § 2050. Kamtz in Poggendorff, xxvii. 345. 
