50 Mr Rowell on the Phenomena of Evaporation. 
in the more fertile lands, but also occurring in barren pastures, and 
even in the more elevated valleys, although few are met with beyond 
the limits of cultivation. The mole frequently bears the name of 
moddiwarp or moddiwort. 
The Carnivora come next; but as among them there are species 
which require a rather lengthened description, it seems expedient to 
reserve them and the Rodentia, among which is a new species, for 
another occasion. 
On the Phenomena of Evaporation, the Formation, and Sus- 
pension of Clouds, §c. By G. A. ROWELL, Esq. of Oxford. 
Communicated by the Author. 
THE phenomena of evaporation, the formation and sus- 
pension of clouds, &c., are so varied, that it is generally 
allowed that no theory hitherto proposed will explain the 
subject satisfactorily, and it is difficult to find authors agree- 
ing to the same explanation. The theory adopted by the 
writer on this subject in the Encyclopedia Britannica (that 
water is taken up in solution in the air), is generally given 
up ; for although it explains evaporation in air very well, it 
does not explain the cause of evaporation in vacuo, or ac- 
count for the formation and suspension of clouds, or how 
clouds obtain their electricity. 
The theory proposed by the late eminent philosopher, Dr 
Dalton, that evaporation is caused by the absorption of caloric 
by water, is adopted by Mr Howard and other leading meteor- 
ologists, but this theory also fails in a similar way; one ob-_ 
jection is, that ice and snow will evaporate when surrounded 
by air below the freezing temperature ; now, as ice is water 
deprived of its 140 degrees of heat of fluidity, from what 
source can it derive its caloric to convert it into vapour, 
when surrounded by a freezing atmosphere ? 
Again, the great heights at which clouds are sometimes 
seen, tell against the theory, as the following will shew the 
enormous expansion of vapour necessary to render it buoyant, 
and, at the same time, the great reduction of temperature at 
such heights. 
