Outlines of a Mechanical Theory of Storms
T >> T. Bassnett >> Outlines of a Mechanical Theory of StormsThe summer of many countries is always dry--California for instance. In
winter, in the same country, the rains are apparently incessant. This of
course depends on the power of the sun, in diverting the great annual
currents of the atmosphere. As long as the dry north-west trade sets
down the coast of California, the circumstances are 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 mensem, pluvia ventisque carebunt."
Hence, also, in the present day we hear sailors speak of the full and
change, or the quartering of the moon, in connection with a gale at sea;
thus showing, at least, their faith in the influence of the phenomenon.
Yet it is actually the case, at certain times, that in about latitude
40d and 41d, the storms appear about a week apart.
There is some reason, also, to suspect, that there is a difference of
temperature on opposite sides of the sun. As the synodical rotation is
nearly identical with the siderent period of the moon, this would
require about forty-four years to run its course, so as to bring the
phenomena to exact coincidence again. Since these observations were
made, it is understood that Sig. Secchi has determined that the
equatorial regions of the sun are hotter than his polar regions. It may
be owing to this fact, that we have inferred a necessity for a change,
whose period is a multiple of the sun's synodical rotation, but it is
worthy of examination by those who possess the necessary conveniences.
Another period which must influence the character of different years,
depends on the conjunction of the perigee of the lunar orbit with the
node. Taking the mean direct motion of the moon's perigee, and the mean
retrograde motion of the node, we find that it takes six years and one
day nearly from conjunction to conjunction. Now, from the principles
laid down, it follows, that when the perigee of the orbit is due north,
and the ascending node in Aries, that the vortices of the earth will
attain their greatest north latitude; and when these conditions are
reversed, the vortices will reach their highest limit in the lowest
latitude. This will materially affect the temperature of the polar
regions. In the following table, we have calculated the times of the
conjunctions of the apogee and pole of the orbit, taking the mean
motions. It may be convenient to refer to by-and-bye, remembering that
when the conjunction takes place due south, the vortices reach the
highest, but when due north, the vortices in the northern hemisphere
have their lowest upper limit:
CONJUNCTION OF APOGEE AND POLE OF ORBIT.[24]
Year. Month and Day. Longitude.
1804, April 18th, 220d
1810, " 17th, 104
1816, " 16th, 348d
1822, " 15th, 232
1828, " 14th, 116
1834, " 12th, 360
1840, " 11th, 244
1846, " 10th, 128
1852, " 9th, 12
1858, " 8th, 255
1864, " 7th, 139
1870, " 6th, 23
1876, " 5th, 267
By this we see that the vortices have never attained their highest limit
during the present century, but that in 1858 their range will be in a
tolerable high latitude, and still higher in 1876--neglecting the
eccentricity of the orbit.
A very potent influence is also due to the heliocentric longitude of the
sun, in determining the character of any given year. Let us explain:
The moon's inertia forces the earth from the mechanical centre of the
terral system, but is never able to force her clear from the central
axis. With the sun it is different. He possesses many satellites
(planets). Jupiter alone, from his great mass and distance, is able to
displace the whole body of the sun. If other planets conspire at the
same side, the centre of the sun may be displaced a million of miles
from the mechanical centre of the solar system. Considering this centre,
therefore, as the centre of an imaginary sun, from which heliocentric
longitudes are reckoned, the longitude of the real sun will vary with
the positions of the great planets of the system. Now, although this
_systematic_ longitude will not be exactly similar to the heliocentric
longitude reckoned from the sun's centre, yet, for the purposes
intended, it will correspond sufficiently, and we shall speak of the
longitude of the sun as if we reckoned heliocentric longitudes from the
mechanical centre of the system. When we come to consider the solar
spots, we shall enter into this more fully. In the following diagram we
shall be able to perceive a cause for variation of seasons in a given
year, as well as for the general character of that year.
[Illustration: Fig. 21]
Let S represent the centre of the sun, and the circle a vertical section
of the sun, cutting; through the centre,--SJ being in the equatorial
plane of the vortex, of which ZZ' represents the axis. As the ether
descends the poles or axis at Z, it is met by the current down the
opposite pole, and is thence deflected in radii along the equatorial
plane to J. But on the side S, the ether is opposed by the body of the
sun; its direction is consequently changed, and cross currents are
produced, assuming it as a principle, that the ethereal fluid is
permeable by other currents of similar matter, and that it tends always
to move in right lines. This granted, it is evident that, in passing the
sun, the quick moving ether forms a conical shell, (the sun being at the
apex,) so that the strongest current of ether is in this conical shell,
or at the surface of this conical space. As the plane of the ecliptic is
not much inclined to the sun's equator, and this last probably not much
inclined to the plane of the vortex, should the earth have the same
_heliocentric_ longitude at the time, (or nearly the same,) she would
be in an eddy, as respects the radial stream, and be protected from its
full force by the body of the sun.
Now, the ether comes down the axis with the temperature of space, and
may possibly derive a _little_ additional temperature in passing over
the body of the sun; so that in this position the earth is protected
from the chilling influence of the radial stream, by being protected by
the body of the sun. And although, from the immense velocity of the
ether, it cannot derive much additional temperature, there may still be
an appreciable difference, due to this cause.
It is the chilling influence of the ethereal stream which originated the
idea among philosophers, of _frigorific impressions, darted from a clear
sky_. In some years the sun will be nearly in the centre of the system;
in other years the axis of the vortex will not come near the sun. And as
the sun's longitude may vary through the entire circle, it may happen
that the earth's longitude shall coincide in winter or summer, or spring
or autumn. When, however, the earth emerges from the protection of the
sun, and enters the conical shell, considered as a space of considerable
depth, she will again be exposed to the full force of the radial stream,
rendered more active by the previous deflection, and by the numerous
cross currents pervading it; so that a mild and calm winter may be
succeeded by a cold and stormy spring. The present season, (1853) the
earth's longitude coincided with the sun's longitude in about 135d, and
consequently was in the conical space spoken of, during February and
March; but the radius vector of the sun's centre, being then less
than 300,000 miles, the protection was not as complete as it is
sometimes. Still, the general fineness of these months was remarkable;
yet in April and May, when the earth became again exposed to the action
of the solar stream, the effect was to retard the spring, and disappoint
the prognostications of the weather-wise. In applying these principles,
we must consider the effect in those latitudes which are more readily
affected,--that is, in the temperate zone, midway between the two
extreme zones of heat and cold.
In 1837 and 1838, the longitude of the sun's centre corresponded with
the earth's, in August and September, when there was neither rain nor
electrical excitement; and consequently those seasons were sickly over
the whole country. Now, there is another cause which renders the months
of August, September, and October, deficient in electrical energy, and
consequently more prone to be sickly. If, therefore, the two causes
unite their influence, the autumnal months will be more sickly at those
times. This last cause, however, only affects the _northern latitudes_
in autumn, and consequently, _ceteris paribus_, the autumnal months
should not be so proverbially sickly in the southern hemisphere. This
is, however, only suggestive.
Again, in 1843, the winter was very mild in January and February; but in
March it turned cold and stormy, and continued through April. In this
year the longitude of the sun was nearly the same as in 1853,--the two
longitudes of the earth and sun corresponding about the last of January;
but in March, the earth forsook the comparative calm produced by the
sun's position, and hence the greater cold.[25]
Thus it appears at every step we take, that the different members of the
solar system do indeed belong to the same family, whose least motions
have their influence on the rest. Who could have anticipated that the
position of Jupiter in his orbit had anything to do with the health of
this remote planet, or with the mildness of its seasons? In this we have
a clue to the origin of that astrological jargon about planetary aspects
being propitious or malign. Philosophers are even yet too prone to wrap
themselves in their mantle of academic lore, and despise the knowledge
of the ancients, while there is reason to believe that the world once
possessed a true insight into the structure of the solar system. As war
became the occupation of mankind, under the despotic rule of ambition,
so truth retired, and ignorance seizing upon her treasures, has so
mutilated and defaced them, that their original beauty no longer
appears. Let us hope that the dawn of a better day is approaching.
There is yet another cause (just alluded to) which modifies the action
of the vortices.
We have shown that, if the periodic times of the planets are
approximately equal to the periodic times of the contiguous parts of the
solar vortex, the density of the ether is directly as the square roots
of the distances from the centre. As the earth is at her perihelion
about the first of January, the density of the surrounding ether is then
less than in other parts of the orbit; consequently, if we suppose that
there is a continual tendency to equilibrium, the ether of space must
press inwards, during the time between the perihelion and aphelion,
(_i.e._ from January to July,) lowering the temperature and increasing
the electrical action of those months. As the distance from the sun is
most rapidly augmenting about the first of April, and the effective
power of the sun's radiation is most rapidly increasing in May; by
combining the two we shall find, that about the first of May we shall
have considerable electrical action, and cold weather. This explains
also, in part, the prevalent tradition of certain days in May being very
cold.[26] When the earth leaves the aphelion, a reaction takes place,
being most rapid in September. There is then an _escape_ of ether from
the earth, which keeps up the temperature, and causes these months to be
sickly, from the negative electrical state of the atmosphere. In the
southern hemisphere, the effects in the same season will be reversed,
which may partly account for the greater degree of cold in that
hemisphere, and for accelerating the approach of both summer and winter,
while in the north they were both retarded.
We must now advert to another cause, which of all others is probably the
most important, at least to the other members of the solar system.
In every part of the solar vortex the ether is continually pressing
outwards. We are not now speaking of the radial stream, but of the
slower spiral motion of the ether around the axis of the vortex, whose
centrifugal force is bearing the whole body of the ether outwards, thus
rarefying the central parts, and thus giving rise to the polar influx,
from which arises the radial stream. This may be made more intelligible,
by reflecting that the polar current is comparatively dense ether, and
that the length of the axis of the vortex prevents this influx current
coming in sufficient quantities to restore an equilibrium in the density
of the medium. Yet, what does come down the poles, is distributed
rapidly along the equatorial plane, leaving the space still rarefied.
Now we perceive, that in order for the radial stream to continue in
action, requires the whole medium of the vortex to be also moving
outward; it is therefore continually condensed as it proceeds. This
condensation necessarily converts much of the specific heat of the ether
into sensible heat; so that the _temperature_ of the medium is
continually increasing, as the distance from the sun increases.
When we contemplate the solar system as the emanation of one Great Mind,
we naturally seek for evidence of the wisdom of a supreme intelligence
in _all_ the arrangements of that system. But, however humbly and
reverently we may speak of these arrangements, we can scarcely avoid the
wish, that the planetary distances had been differently arranged, if
Newton's doctrine be true, that space is a vacuum, and that the heat of
a planet, is inversely as the squares of the distances from the sun.
For, to speak of the temperature of space, except as dependent on this
law, is one of those many incomprehensible inconsistencies with which
philosophers are chargeable. If the Newtonian philosophy is literally
true, space has _no temperature_, and the surface heat of the planet
Neptune is nearly 1,000 times less than on our own globe. Again, on
Mercury it is seven times greater, which heat would scorch and consume
every organic substance on the earth, and speedily envelope the boiling
ocean in a shroud of impermeable vapor. Granting even that space may not
be a vacuum, and yet the law of gravitation be true, we may still be
allowed to consider both Saturn and Uranus and Neptune, as inhospitable
abodes for intelligent creatures; and, seeing the immensity of room in
the system, there is no reason why these planets might not have been
permitted to revolve nearer the great source of light and life and
cheering emanations. To suggest the resources of Omnipotence is no
argument. He has surrounded us with analogies which are seen, by which
we may attain a knowledge of those which are not seen; and we have every
reason to suppose that the great Author of nature is not indifferent to
the aspects under which his works reveal him unto his creatures. Yet
there is (on the above hypothesis) an apparent want of harmony in the
planetary distances; and if frail mortality may be permitted to speak
out, an explanation is needed to obviate this seeming anomaly in the
economy of the world. The more we learn of the physical arrangements of
the universe, the more do they correspond with our experience of the
nice adaptation of the means to the end which obtains in our own globe,
and we can only judge of other planets by the analogies around us. Here,
there, are extremes of temperature it is true: it is necessary there
should be, and we can see and understand the necessity in all such
cases, and how they conduce to the general average of good. But,
astronomers can give no reason why it is necessary that some planets of
our system should be placed so remote that the sun is frittered down to
a star, whose heatless light is but a mockery to those frigid realms.
Now, according to this theory, the temperature of Neptune may be far
more uniform and conducive to life than that of our own globe. The
chilling influence of the solar stream at that planet being nearly null,
and the temperature of the surrounding space far greater. So also
Mercury, instead of being the burning planet of the schools, may suffer
the most from cold.
The planet Mars is generally considered, of all the members of the
system, most nearly to resemble our own world. The telescope not only
reveals seas and continents, but the snowy circles round his poles,
which appear to increase and diminish, as his winter is beginning or
ending. This planet's ecliptic is similar to our own in inclination or
obliquity, his distance, also, is far greater, and his winter longer;
yet, for all this, his snow zones are less than on our own globe. This
anomalous fact has, we believe, never been noticed before; but it is
explicable on the theory, and therefore confirms it. Mars has no
satellite, and therefore his centre will be coincident with the centre
of the marsial vortex. There will be no _lateral vortices_ to derange
his atmosphere, and if the axis of his vortex coincides also with the
axis of the planet, the central vortex will be continually over the
poles, _and there will be no storms on the planet Mars_. A capital fact
connected with this, is the want of belts, as in Jupiter and Saturn; for
these planets have satellites, and if _they_ are not massive enough, the
belts may be produced by an obliquity in the axis of the Jovial and
Saturnial vortices. If Mars had an aurora like the earth, it is fair to
presume the telescope would ere this have shown it. He is, therefore, in
equilibrium. In applying this reasoning to the earth, we perceive that a
certain influence is due to the difference of temperature of the
ethereal medium surrounding the earth, at perihelion and aphelion, being
least at the former, and greatest at the latter.
As a modifying and interfering cause in the action of the vortices, we
must mention the great natural currents of the atmosphere, due to the
earth's rotation.
It is considered that the sun is the principal cause of these great
currents. By elevating the surface atmosphere of the equator, a lateral
current is induced from the north and south; but on account of the
enlarging circles of latitude, their direction tends more from the
north-east and south-east. These currents are usually called the trades.
Without disputing the correctness of this, it may be doubted whether the
whole effect is due to the sun. As this principle affects the ocean
likewise, it is necessary to look into it; and in order to simplify the
question, we will first suppose our globe covered entirely by the ocean,
without any protuberant land.
Let us assign a uniform depth of ten miles to this ocean. In the Fig.
following, the two circles will represent the surface and bottom of the
ocean respectively. The axis of rotation is thus represented by the line
PP'. Let us consider two particles of water at m and n, as feeling the
influence of this rotation; they will, of course, be both urged towards
the equator by the axifugal force. Now, every particle in the ocean
being also urged by the same force, it might be supposed that after a
protuberant mass of water had accumulated at the equator EE', the whole
ocean would be in equilibrium. This would not follow. The particle at m
is urged by a greater force than n; consequently the particle at n is
overborne by the pressure at m. Considering both in the same direction,
yet the particle at n must give way, and move in the opposite direction.
Just as the heaviest scale of the balance bears up the lightest,
although both gravitate towards the same point. This is so self-evident
that it would seem unnecessary to dwell upon it, had not the scientific
world decided that the rotation of the earth can cause no currents
either in the atmosphere or in the ocean.
[Illustration: Fig. 22]
The axifugal forces of the two particles m and n are directly as the
lines Mm and Nn, and if the gravitating forces were also as the radii Tm
and Tn, no motion would be produced. Admitting even the Newtonian law to
be rigidly exact, the earth cannot be considered a homogeneous globe,
but, on the contrary, the density of the central parts must be nearly
thirty times greater than the density of the surface of the ocean. The
ratio of the gravitating forces of these two particles is, therefore,
less than the ratio of their respective radii, and the axifugal tendency
of the particle at n is more than proportionally restrained by the
central gravitation; and hence m will move towards the equator, and n
towards the poles, as represented in the Fig.
It is on account of the overwhelming momentum of the surface waters of
the South Pacific over the North, that the Pacific, at Panama, stands
six or seven feet higher than the Atlantic. We shall again allude to
this interesting fact.
According to newspaper reports of a lecture, delivered in New York, by
Lieut. Maury, U. S. N., this gentleman endeavors to explain the currents
of the ocean, by referring them to evaporation in the tropics. The vapor
leaves the salt of the water behind, and thus, by continual
accumulation, the specific gravity of the tropical waters is greater
than that of the superficial waters nearer the poles; the lighter
water, therefore, passes towards the equator, and the heavier water
below, towards the poles. If this be a correct statement of that
gentleman's theory, fidelity to our standards compels us to question the
soundness of the conclusion. The mere fact of the surface water of the
ocean being lighter than that of the bottom, cannot on any known
principles of science cause any movement of the surface waters towards
the equator. When such an acute and practical physicist is driven, by
the palpability of the fact that the polar waters are continually
tending towards the equator, to seek the cause in the tropical
evaporation, it shows that the dogma, which teaches that rotation can
produce no motion, is unsound.
Sir John Herschel, in speaking of the solar spots, says: "We may also
observe that the tranquillity of the sun's polar, as compared with his
equatorial regions (if his spots be really atmospheric), cannot be
accounted for by its rotation on its axis only, but must arise from some
cause external to the sun, as we see the belts of Jupiter and Saturn and
our trade winds arise from a cause external to these planets combining
itself with their rotations, which _alone_ (and he lays an emphasis on
the word) can produce no motions when once the form of equilibrium is
attained."
With respect to the origin of the solar spots, we have no disposition to
question the conclusion; but, as regards the _principle_ laid down, that
rotation can produce no motions when once the form of equilibrium is
attained, we must unequivocally dispute it. If our atmosphere were of
uniform density, the rotation of the earth would cause no current such
as we have described; with our atmosphere as it is, the result will be
different. The momenta of two portions of matter are the products of
their inertiae by their motions, and, in the present case, we must take
the inertiae of equal spaces. A cubic inch of air at the surface, and at
three miles above the surface, is as 2 to 1; but their centrifugal
velocity varies only as the radii of the respective spheres, or as 1320
to 1321. In the polar regions, therefore, the momentum of the surface
air preponderates, and, in this case, the _surface_ current is towards
the equator, and the upper current towards the poles. When, however, the
centrifugal velocity is considerably increased in a lower latitude, and
the curvature of the surface becomes more and more inclined to the
direction of that resolved part of the centrifugal force, which is
always _from_ the axis, the surface layers will evince a tendency to
leave the surface, and an intermingling will then take place in the
space between latitude 70d and 50d, or in latitude 60d. As this layer is
continually urged on in the same direction by the surface layer of
latitudes above 60d, the upper layer now becomes a current setting
_towards_ the equator, and, consequently, the back current occupies the
surface. Now, considering that the rarefying action of the sun is
elevating the air under the equator, there must necessarily be an upper
current from the equator to the poles; so that if we conceive the two
currents to meet about latitude 30d, there will be a second
intermingling, and the current from the poles will again occupy the
surface. Thus, we regard a part of the effect of the trades to the
rotation of the earth, which is the chief impelling power at the poles,
as the sun is at the equator; and the latitudes 60d and 30d will be
marked by some especial phenomena of temperature, and other
meteorological features which do actually obtain. These would be much
more marked if the irregular configuration of land and sea, the
existence of mountain chains, and the different heating power of
different latitudes, owing to the unequal distribution of the land, did
not interfere; and the currents of the air (disregarding the deflection
east and west) might then be represented by a treble link or loop, whose
nodes would vary but little from latitudes 30d and 60d. As it is, it
has, no doubt, its influence, although unimportant, when compared with
the disturbing action of the ethereal vortices.