re not favorable for
giving full development to the action of the vortices. When the trade
wind ceases, and the prevailing winds come from the south, loaded with
vapor, the vortices produce storms of any magnitude; but (and we speak
from two years' observation) the passages of the vortices are as
distinctly marked there in winter time, as they are in the eastern
States; and in summer time, also, they are very perceptible. The same
remark applies to Mediterranean countries, particularly to Syria and
Asia Minor; although the author's opportunity for observing lasted only
from April to December, during one season. If we are told it never rains
on the coast of Peru, or in Upper Egypt, it does not seriously militate
against the theory. The cause is local, and the Samiel and the sand
storm of the desert, is but another phase of the question, explicable on
the same general principles. From the preceding remarks it will be seen,
that in order to foretell the character of particular days, a previous
knowledge of the weather at that particular place, and for some
considerable time, is requisite; and hence the difficulty of laying down
general rules, until the theory is more fully understood.

MODIFYING CAUSES.

We now come to the causes which are auxiliary and interfering. It is
natural that we should regard the sun as the first and most influential
of these causes, as being the source of that variation in the
temperature of the globe, which alternately clothes the colder regions
in snow and verdure. The heat of the sun undoubtedly causes the ether of
the lower atmosphere to ascend, not by diminution of its specific
gravity; for it has no ponderosity; but precisely by increase of
tension, due to increase of motion. This aids the ascensional movement
of the air, and therefore, when a vortex is in conjunction with the sun,
its action is increased--the greatest effect being produced when the
vortex comes to the meridian a little before the sun. This has a
tendency to make the period of action to appear dependent on the phases
of the moon, which being the most palpable of all the moon's variations,
has been naturally regarded by mankind as the true _cause_ of the
changes of the weather. Thus Virgil in his Georgics, speaking of the
moon's influence and its signs:

"Sin ortu in quarto (Namque is certissimus auctor)
Pura, nec obtusis per coelum cornibus ibit;
Totus et ille dies, et qui nascentur ab illo,
Exactum ad