24 G Mr Blackadder on circumstances connected with the 
has caused the precipitation, afterwards becomes surrounded by 
a body of air that is not saturated, its temperature may be re- 
duced by evaporation below that of the contiguous air. In the 
course of nature, however, this can be but a rare occurrence. 
As it is impossible to acquire any accurate geological know- 
ledge, by examining the appearances exhibited by a single quar- 
ry, mine or cliff, or by several such places, more especially when 
the locality, &c. is not greatly different, so is it with meteoro- 
logy, as it regards the phenomena exhibited by the vaporisation 
and condensation of water ; mountain, hill, and valley, — dry 
plain and marshy meadow, — the sea and fresh-water lakes, 
rivers and stagnant ditches, must all be familiar, and the ap- 
pearances there exhibited carefully attended to, before any ac- 
curate estimate can be formed of the causes which operate in 
modifying the spontaneous formation and reduction of aqueous 
vapour. In this point of view, Dr Wells was unfavourably si- 
tuated ; but he has given us an excellent example of what zeal 
and perseverance, aided by a masculine intellect, may effect, 
even in very unpromising circumstances. 
On one occasion, in the month of July, during a tract of 
fine weather, and immediately on sunset, I had an oppor- 
tunity of witnessing a very interesting exhibition of that mo- 
tion which takes place in the lower air, at a time when the 
atmosphere might, by persons not conversant with meteoro- 
logical pursuits, be considered perfectly tranquil. It was an 
evening, as described by the poet, when “ a solemn stillness 
reigns.” The scene was a perfectly level meadow, destitute 
of trees, hut in which were a few straggling sheep and cows ; 
and it was surrounded on all sides by rising grounds, vary- 
ing, of small elevation, but rising gently as they receded. 
The place from which it was viewed was about 50 feet above 
the level, and within less than a gunshot of the side of the 
meadow, commanding a complete view of the whole. Sudden- 
ly the eye was arrested by a very low white mist, steaming 
from the whole surface of the meadow. At first it did not ex- 
tend higher than the legs of the sheep, and had throughout a 
peculiar indefinite agitated motion, resembling small broken 
waves, not advancing in any horizontal direction. In the course 
