On the Clouds. 391 
Our own country is so extensive, and embraces so many parallels 
of latitude and longitude, that it presents a great variety of 
climates as well as local features that exert their respective in- 
fluence upon the wjeather; it would be impossible to fix even 
within approximation the mean annual amount of rain for the 
United States, in fact so few are the observations, so brief and 
unsatisfactory are the data, that I regret to say it, we know 
nothing at all about it. The state of Pennsylvania adopted a 
useful course in relation to meteorological science, by supplying 
each county in the state with a set of instruments, the observations 
from which were directed to be reported to the Franklin Institute 
at Philadelphia, by which means much useful information relative 
to meteorology of the state is annually obtained. 
It has been found by repeated experiments that more rain is 
collected in the rain guage when placed near the earth, than when 
placed at a distance from it, as upon the top of a building, or 
other elevated structure; we can only account for this by sup- 
posing that the vapour near the earth is more dense, and gradually 
expands as it rises in the atmosphere, and when the latter is in a 
condition to convert the vapor into rain, it will have a greater 
quantity to condense near the earth than at a higher point of 
atmosphere. 
The tendency of rain is to soften and moisten the ground, and 
put it in a condition to convey nutriment to vegetation, and by 
falling upon ranges of elevated land to convey to the plains fer- 
tilizing particles of soil, washed from their mellowed surface; and 
while it tends to purify the air, at the same time contributes its 
fertilizing influence to the soil. It moderates the heat of the 
surrounding atmosphere, and forms the source of every stream or 
river that irrigates the land. All no doubt have observed the 
beneficial effects of rain water upon the vegetation of plants, and 
the blighting effects produced by a want of it; how after a shower 
in the spring or summer, vegetation assumes a greener hue, and 
more luxuriant growth. A superabundance of rain may have an 
injurious influence upon crops by destroying the cohesion of the 
soil, and their consequent prostration, together with the dispersion 
of the soluble particles which are borne away by the temporary 
rills and streams, visible after a heavy rain, into the reservoirs of 
the vicinity, or the low bottoms where there is not descent suf- 
ficient to carry them further. 
It seems the greatest quantity of rain falls during the months 
whose temperature is highest; consequently the summer months 
are productive of the most rain, whilst the colder months exhibit 
the greatest number of cloudy and rainy days. 
In some countries excessive rains are found to be accompanied 
with barrenness and sterility of the land in the ensuing season, 
