Having thus taken a brief view of the different clouds, let us return to
the inquiry, from what ocean, and by what machinery, _our_ "rivers
return."
Not wholly or mainly from the North Atlantic, although it lies adjacent to
us, and they often _seem_ to do so; for, first, all storms, showers, and
clouds, which furnish, _independently_, any appreciable quantity of rain
to the United States, and even adjacent to the Atlantic, or indeed to the
Atlantic itself, come from a westerly point, and pass to the eastward.
_This is a general, uniform, and invariable law, although there is in
different places, and in the same place at different times, some variation
in their direction; ranging in storms from W. by S. to S. S. W., and in
showers between S. W. and N. W., to the opposite easterly points of the
compass; the most general direction, east of the Alleghanies, being from
W. S. W. to E. N. E._
But do we not see, you inquire--at least those of us who live east of the
Alleghanies--that when it rains, the wind is from the eastward; and that
the _clouds_ follow the wind from the east to the west? You do indeed,
generally, in all considerable storms, observe that the wind blows from
some easterly point, and that _seeming_ clouds are blown by it to the
westward; but what you see, and call clouds, are not the clouds which
furnish the rain. Far above the seeming clouds you notice, directly over
your head when it rains or snows, are the rain or snow clouds, dense and
dark, passing to the eastward, how strong soever the wind may blow from
the quarter to which they tend, or any other quarter, between you and
them. What you see below them are _scud_. So the sailors call them, and so
I have termed them. It is a "dictionary name," and a good one, expressive
of a distinction between them and _clouds_. They are thin, and the sun
shines through them, although with some difficulty, when the rain clouds
above are absent or broken. _This east wind and the scud are not the
storm, or essential parts of it._ Storms occasionally exist, particularly
in April, without either. They are but _incidents_, _useful_, but not
_necessary incidents_, as all surface winds are.
If you could see a section of the storm, you would see the rain cloud
above, moving to the east, and the scud beneath running to the west, as
indicated by the arrows in the cut on page 40. Opportunities frequently
occur when these appearances may be seen. Storms are sometimes very long,
a thousand miles, perhaps, from W. S. W. to E. N. E., and not more than
one to three hundred miles wide from S. E. to N. W., and their sides,
particularly the northern ones, regular, and without extensive partial
condensation. Then the storm cloud above, moving to the eastward, and the
scud running under to the westward, may be seen as in the cut.
So they may be seen before, at the commencement, and at the conclusion of
easterly storms, in a majority of cases, and the reader is desired to
notice them particularly as opportunities occur.
The term _running_, too, is a very expressive one, used by sailors as
applicable to _scud_. For while the forming or formed storm clouds may be
moving moderately along, at the rate of twelve to fifteen or twenty miles
an hour, from about W. S. W. to E. N. E., the scud may be running under
them in a different direction--opposite, or diagonal, or both--at the rate
of twenty, fifty, sixty, and, in hurricanes, even ninety miles an hour.
You have doubtless seen these scud running from N. E. to S. W., and
without dropping any moisture, a day or sometimes two days, before the
storm coming from the S. W. reached the place where you were; and then,
sometimes the storm cloud slipped by to the southward, and the expected
storm at that point proved "a dry northeaster." Sometimes the
condensation, although sufficiently dense to influence and attract the
surface atmosphere, and create an easterly wind and scud, does not become
sufficiently dense to drop rain, and then, too, we have a dry northeaster,
which may melt away or increase to a storm after it has passed over us. _I
have never seen, except, perhaps, in a single instance, one of these
masses of scud, however dense, which had not a rain (stratus) cloud above
it, drop moisture enough to make the eaves run._ So you see it may be
true, and if you will examine carefully, you may satisfy yourself that it
is true, that the storms all move from a westerly point to the eastward,
notwithstanding the wind under them is blowing, and the scud under them
are running to the westward.
There are many other methods by which the reader may determine this matter
himself. He may catch an opportunity for a view, when there is a break in
the stratus cloud above, and the sun or moon, no longer obscured by the
_storm cloud_, shines through the scud beneath. Then he may see they are
moving in different directions. _The upper cloud, if there be any of it
left, always to the eastward._
Again, we may see the storm approach from the westward, as it often does,
before the wind commences to blow, and the scud to run from the eastward;
particularly snow storms in winter, and the gentle showers and storms of
spring.
Again, thunder storms, we know, come from the westward, and apparently
against an east wind. It is sometimes said they approach from the east,
but it is a mistake. During thirty years attentive observation in
different localities, I have never seen an instance. They sometimes _form_
over us, or just east of us, or one may form at the east and another at
the west, and as they _spread out in forming_, one may seem to be coming
from the east, or there may be an easterly current, with dense flocculent
scud at the under surface of the shower cloud running westward, but they
finally pass off to the eastward, and never to the westward. It is
possible that a _patch of scud_ may become sufficiently _dense_ and
_electrified_ to make a _shower_, but I have never observed one. Such an
_apparent_ instance may be found recorded in "Sillman's Journal," vol.
xxxix. page 57. I have seen the scud assume a distinct cumulus form, but
never to become sufficiently dense to make a thunder shower.
Thunder and lightning sometimes attend portions of regular storms in
spring and autumn, but the thunder is always heard first in the west, and
last in the east.
Again, there are admitted facts with which you are conversant, which prove
this proposition. When it has been raining all day, and just at night the
storm has nearly all passed over to the eastward, and the sun shines under
the western edge of it, and "_sets clear_," as it is termed--you say that
"_it will be clear the next day_." Why? Because the storm will not pass to
the westward, covering the sun and continuing, how strong soever the wind
may be from the east; and because it is passing, and will continue to pass
off to the eastward, leaving the sky clear. _The easterly wind will stop
as soon as the storm clouds have passed, and it will fall calm, or the
wind will "come out" from the westward._
So, too, when the clouds are dark in the west in the morning, and the sun
rises clear, but "_goes into a cloud_," as it is expressed, you say that
it will rain. And if the clouds are dense this generally proves true;
because there is a storm or shower approaching from the west, and passing
over to the east, the western edge of whose advance condensation has met
the sun in his coming, and obscured him from your vision.
When, too, it has been storming, and lights up in the N. W. you say it
will clear off; the N. W. wind will blow all the clouds away. It is,
indeed, generally true that when it so lights up it is about to clear off;
although it sometimes shuts down again, in consequence of the approach of
another storm from the westward, following closely behind the one which is
passing off. It is a great mistake, however, to suppose the N. W. wind
blows away the clouds. Watch the smooth stratus rain cloud at its lower
edge, where the clear sky is seen, and you will see that it is moving on
steadily to the N. E., in obedience to the laws of its current, and will
do so, even when its retreating edge has passed up to the zenith, and down
to the S. E.
The storm uncovers us from the N. W. by the contraction of its width, _or_
because it has a _southern lateral extension_ and _dissolution_, and not
by being blown away by the N. W. wind; although that wind, by its peculiar
fair-weather clouds, may be, perhaps, observed beneath, ready to follow
its retreating edge.
Again, when it has been clear all day, and the sun sets in a bank of
cloud, you say--"_it will rain to-morrow, the sun did not set clear_," and
unless that bank is a thunder cloud, merely, which will pass over or by
you, with or without rain, before morning, it is generally true that it
will. The bank will prove the eastern edge of an approaching storm.
From these generally admitted and understood facts, you may know that
storms pass from the west to the east.
This proposition is also proved by all the investigations of storms, which
have taken place since the settlement of this country. Storms of great
severity attract particular attention, and are said to "back up" against
the wind, because they are observed to commence storming first at the
westward, although the wind is from the eastward. Doubtless you recollect
many such instances recorded in the newspapers. No season occurs without
such notices.
Many storms have been investigated by Mr. Redfield, for the purpose of
sustaining his theory. Many others by Professor Espy, to sustain his. One
by Professor Loomis, with great research and ability--and some by others,
accounts of all which have been published; and every one yet investigated,
north of the parallel of 30 deg., has been shown to pass from a westerly to an
easterly point.
So, too, we may know it from analogy. The laws of nature are uniform.
There is a great end to be accomplished, _viz._: the distribution of forty
inches of water, at regular intervals, over a large extent of country. The
rivers are to return, and the clouds are to drop fatness, and seed time
and harvest are not to cease. It is to be done and is done, by means of
storms and showers, and pursuant to general laws, as immutable as the
result. Most of these storms and showers, it has been found, and may be
observed, move from the westward to the eastward. Then we may know, from
analogy, that they do so in obedience to a general, uniform law; and so I
might say with confidence, if our inquiry stopped here, it will ever be
found by those who may hereafter examine them.
But, 2d. There is a current in the atmosphere, all over the continent
north of the N. E. trades, but in great volume over the United States,
east of the meridian of 105 deg. W. from Greenwich--varying in different
seasons, and upon different parallels, and flowing near the earth, when no
surface wind interposes between them. In the vicinity of New York, the
usual course of this current is from about W. S. W. to E. N. E. In the
western and south-western portion of the United States, it is, doubtless,
more southerly--varying somewhat according to the season--and in other
sections varies in obedience to the general law of its origin, and
progress.
I have observed its course in many places, between the parallels of 38 deg.
and 44 deg. N. _This current comes from the South Atlantic Ocean._ It is our
portion of the aerial current, which flows every where from the tropics
toward the poles, to which I have already alluded in connection with the
distribution of heat. _It brings to us the twenty inches of rain which we
lose by the rivers, and by the westerly winds, which carry off a portion
of the local moisture of evaporation, and its action precipitates the
remaining portion of that moisture. It spreads out over the face of our
country, with considerable, but not entire uniformity. All our great
storms originate in it, and all our showers originate in or are induced
and controlled by it._
_From the varied action, inherent or induced, of this current, most of our
meteorological phenomena, whether of wet or dry, or cold or warm weather,
result_; and a thorough knowledge of its origin, cause, and the reciprocal
action between it and the earth, is essential to a knowledge of the
"_Philosophy of the Weather_."
Let us then go down to the "chambers of the south," to the inter-tropical
regions, of which we have said something in connection with a notice of
Southern Mexico, and see where, and how this great aerial current
originates.