fluence exerted by the moon upon the weather, in relation to
which we have any reliable practical data.

Humboldt appears to have adopted the impression of Sir W. Herschell, that
the moon aids in the dispersion of the clouds. (Cosmos, vol. iv. p. 502.)
But the tendency to such dispersion is always rapid during the latter part
of the day and evening, when there is no storm approaching, and the full
moon renders their dissolution visible, and attracts attention to them.
The Greenwich observations, also, carefully examined by Professor Loomis,
fail to confirm the impression of Herschell and Humboldt, and those
eminent philosophers are doubtless in this mistaken.

From this general and somewhat desultory view of the general facts, which
bear analogically upon the question, no decisive inference can be drawn in
relation to the seat of the primary influence which produces the
atmospheric changes. The preponderance is in favor of the magnetic, or
magneto-electric, action of the earth. We must come back to our own
country and grapple with the question at home.

CHAPTER IX.

Before proceeding to do this, however, it may be well to look at some
theories which have been advanced, and to a greater or less extent
adopted, and at their bearing upon the question.

The calorific theory is at present the prevailing one in Europe and in
this country. Meteorologists there and here refer all atmospheric
conditions and phenomena to the influence of heat. The principal
applications of that theory have been considered. But within the last few
years the elasticity and tension of the aqueous vapor of the atmosphere
have received much attention, as exerting an auxiliary or modifying
influence. Professor Dove, of Berlin, who ranks perhaps as the most
distinguished meteorologist of that continent, attributes barometric
variations to _lateral overflows_, and, in the upper regions, resulting
from the elevation of the atmosphere by expansion; and in this view
meteorologists of Europe seem generally to acquiesce. In an article sent
to Colonel Sabine, and recently republished in the American Journal of
Science, January, 1855, in thus attempting to account for the annual
variation of barometric pressure, which occurs in Europe and Asia, and,
indeed, over the entire hemisphere. He says:

"From the combined action or the variations of aqueous vapor, and of
the dry air, we derive immediately the periodical variations of the
who