constantly recruited from the atmosphere as the storm-centre travels
along,--was new wool not forthcoming from the white sheep and the black
sheep that the winds herd at every point,--all rains would be brief and
local; the storm would quickly exhaust itself, as we sometimes see a
thunder-cloud do in summer. A storm will originate in the far West or
Southwest--those hatching-places of all our storms--and travel across
the continent, and across the Atlantic to Europe, pouring down
incalculable quantities of rain as it progresses and recruiting as it
wastes. It is a moving vortex, into which the outlying moisture of the
atmosphere is being constantly drawn and precipitated. It is not
properly the storm that travels, but the low pressure, the storm
impulse, the meteorological magnet that makes the storm wherever its
presence may be. The clouds are not watering-carts, that are driven all
the way from Arizona or Colorado to Europe, but growths, developments
that spring up as the Storm-deity moves his wand across the land. In
advance of the storm, you may often see the clouds grow; the
condensation of the moisture into vapor is a visible process; slender,
spiculæ-like clouds expand, deepen, and lengthen; in the rear of the
low pressure, the reverse process, or the wasting of the clouds, may be
witnessed. In summer, the recruiting of a thunder-storm is often very
marked. I have seen the clouds file as straight across the sky toward a
growing storm or thunder-head in the horizon as soldiers hastening to
the point of attack or defense. They would grow more and more black and
threatening as they advanced, and actually seemed to be driven by more
urgent winds than certain other clouds. They were, no doubt, more in
the line of the storm influence. All our general storms are cyclonic in
their character, that is, rotary and progressive. Their type may be
seen in every little whirlpool that goes down the swollen current of
the river; and in our hemisphere they revolve in the same direction,
namely, from right to left, or in opposition to the hands of a watch.