250 
SECOND REPORT -1832. 
y"~-v 
which however but imperfectly represents the observations. 
The causes which regulate the amount of rain in different lati¬ 
tudes, have been well pointed out by Dr. Anderson in the 
Essay on Hygrometry before alluded to *. 
A less explicable variation takes place in the fall of rain at 
different heights. And here a distinction, not always enough at¬ 
tended to, must be pointed out. The quantity of rain which falls 
on high grounds exceeds that at the level of the sea; hut the 
amount at stations abruptly elevated above the surface of the 
earth diminishes as we ascend. For example, at Kinfauns 
Castle, Perthshire, by a mean of five years, 25*66 inches of rain 
fell; whilst on a hill in the neighbourhood, 600 feet higher, 
no less than 41*49 inches were collected by a mean of the same 
period f. On the other hand, at Paris, whilst 56*37 centime¬ 
tres of rain fall in the court of the Observatory, according to 
Arago, only 50*47 fall on the tower at a vertical height of 28 
metres. The former fact may readily be explained by the in¬ 
fluence of a hilly country in retaining clouds and vapours ; but 
the latter seems yet to have met with no satisfactory explana¬ 
tion, nor has any theory having even novelty to recommend it 
been recently proposed. The interesting observations esta¬ 
blished at York Minster, at the suggestion of the British As¬ 
sociation, and under the active superintendance of my friends 
Mr. Phillips and Mr. Gray, jun., will soon, I am certain, afford 
us valuable information on this curious subject. 
The very interesting comparative registers kept at Geneva 
and at the Convent of the Grand St. Bernard, have not failed 
to illustrate the influence of a mountainous country on the fall 
of rain. From the results published in the Bibliotheque Univer- 
selle , it appears that the amount at the latter point is double 
that at the former J. Mr. Dalton, in an interesting paper upon 
these observations, which has just appeared §, points out in a 
clear manner the influence of hot currents of air ascending by 
the surface of the ground into the colder strata which rest upon 
a mountainous country. The consequence is, that although 
neither the hot nor the cold air was accompanied with more 
moisture than could separately be maintained in an elastic 
state, when the mixture takes place, the arithmetical mean of 
the quantities of vapour cannot be supported in an elastic state 
at the arithmetical mean of the temperatures, since we have 
seen that the weights of vapour which can exist in a given 
space, increase nearly in a geometrical ratio when the tempe¬ 
ratures follow an arithmetical one. 
* Edinburgh Encyclopaedia, vol. xi. f Ibid. Art. Meteorology. 
X Bibliotheque Universelle, Mars ]828. 
§ Manchester Transactions, New Series, v. 233. 
