390 On the Clouds. 
uniformity in their size, and perhaps the eye might number twenty 
of them above the horizon. Upon attaining the superior elevation 
of the country, a broad extent entirely uninterrupted presented 
itself, forming a circuit of many miles. At intervals of distance, 
I observed several columns of smoke ascending, apparently pro- 
duced by the burning of logs upon new clearings; the lower 
stratum of air was perfectly calm, so that the columns arose per- 
pendicularly from the earth; the next stratum above had a very 
gentle motion from the east, which imparted to the clouds a barely 
perceptible westerly progress; as they respectively approached the 
vicinity of the columns, they swerved from their direct course, and 
became stationary for a short time over them, and gradually dis- 
appear in the ascending smoke. 
Vapors are supposed to be merely small bubbles or vesiculae, 
arising 'from the surface of the earth, mainly through the in- 
fluence of heat. These vesiculae being specifically lighter than 
the atmosphere, are buoyed up by it, until they arrive at a region 
where the air is of that degree of density to form an equilibrium 
with them, until by some new agent they are converted into 
clouds, and thence descend in the shape of rain, snow, hail, or 
mist. The cause of the precipitation of rain is perhaps not yet 
accounted for in a satisfactory manner; it rests principally upon 
theories, which owing to our slight connexion with the upper 
strata of the atmosphere, and the few observers upon elevated 
positions, are as yet imperfect, and not sufficiently supported by 
observation and experiment. The observations made upon ele- 
vated points by men of science, have been few and hasty, and 
have not tended materially to elucidate the subject. It does not 
seem probable that the moon exerts any influence upon the 
atmosphere so far as rain is concerned, the effect of its attraction 
as shown by calculation being so very slight; as also exemplified 
in the little consistencies in the observations advanced in favor of 
such a theory. As a general rule, the quantity of rain which 
falls is greatest at the equator, and diminishes toward the pole, 
although this rule is much modified by local causes. It is staled 
that in some parts of St. Domingo the annual amount of rain is 
150 inches, while at St. Petersburgh, in Russia, it is but about 17 
inches, at Paris it is 19 inches, and at Pisa, in Italy, 43 inches. 
In England there is a great difference in the annual quantity of 
rain that falls at various points, for instance 
inches. inches. 
At Keswick, in Cumberland, 67 
Plymouth, 46 
Lancaster, — 45 
Dover, 37 
At Manchester, 33 
Bristol, 29 
London, - 23 
Upminster, 19 
The mean annual amount for England, is estimated at 35 inches 
