hurricane are seen to the S., S. E., and E. S. E., according to the season
of the year, as we see them at the westward. During the rainy season, and
when the storm, as is usual at that period, is small, and the S. E. trade
blows more eastwardly, the wind at the Windward Islands, possibly, may set
in at the north, and back round by the east as it progresses. So Colonel
Reid thinks it sometimes does, at Barbadoes. But when the belt of rains is
south, and the hurricane comes from the south-east, and is larger and more
violent in its action, and the north-east winds prevail, the first effect
is an increase of these trades. Soon, however, the wind hauls to the north
and north-west, in opposition to its course, bearing the same relation to
it that our east and north-east winds bear to storms in the United States;
and the wind hauls around during the passage of the storm to the west,
south-west, and south-east, and at the latter point it clears off. Mr.
Edwards in his History of Jamaica says--and as a resident, his authority
should be decisive as to this Island--"_that all hurricanes begin from the
north_, veer back to the W. N. W., W., and S. S. W., and when they get
around to the S. E. the foul weather breaks up." Doubtless the same is
true of the class of northers of which we are speaking on the Gulf of
Mexico. _But with this class the barometer does not rise during the gale,
and in proportion to its length and violence._ With the other class of N.
W. winds--the northers of winter--it does.
The following description of two winter northers, copied from Colonel
Reid's valuable work, will illustrate what has been said. _Precisely such
changes from S. E. rains to N. W. winds, with blue sky and detached dark
clouds--fair-weather N. W. scud--occur every autumn in October and
November_, and the falling of the thermometer and rising of the barometer,
after rain, and a change of the wind, are perfectly characteristic.
------------------------------------------------------------------------
1843. | Wind. |Force.|Weather.| Bar.|Ther.|
------------------------------------------------------------------------
Jan. 30.| | | | | |
A.M. 4. |S. S. W. | 2 |b. c. |29.90| 77 |Off Tampico.
Noon. |South. | 5 |b. c. r.|29.86| 76 | {Lat. 23 deg. 41' N.,
P.M. 8. |South. | 6 |b. c. r.|29.84| 76 | {Long. 94 deg. 50' W.
Jan. 31.| | | | | |
A.M. 4. |S. Easterly.| 3 |b. c. |29.90| 74 | {Between 6 and 10
| | | | | | {A.M., wind was
| | | | | | {variable.
Noon. |N. by W. | 9 |c. q. w.|29.96| 76 |Norther commenced at
| | | | | | 10 A. M.
P.M. 8. |N. N. W. | 9 |c. |30.09| 73 |Lat. 22 deg. 36' N.,
| | | | | | Long. 95 deg. 48' W.
Feb. 1. | | | | | |
A.M. 4. |N. N. W. | 7 |c. g. |30.29| 63 |Lat. 22 deg. 9' N.,
| | | | | | Long. 94 deg. 50' W.
Noon. |Westerly. | 6 |c. |30.30| 67 |
P.M. 8. |Calm. | 0 |c. |30.26| 67 |
------------------------------------------------------------------------
Feb. 14.| | | | | |
A.M. 4. |S. E. | 3 |b. c. r.|29.66| 73 |At Sacraficios.
Noon. |S. W. | 4 |b. c. |29.62| |Norther comc'd at 5.30
| | | | | | P.M.
P.M. 8. |N. W. by N. | 10 |c. q. u.|29.72| 65 |
Feb. 15.| | | | | |
A.M. 4. |N. W. by N. | 10 |c. q. u.|30.10| 61 | {Gale moderated and
| | | | | | {again freshened
| | | | | | {about 8 A.M.
Noon. |N. W. by N. | 10 |c. g. q.|30.19| 61 |
P.M. 8. |N. W. | 4 |c. g. |30.20| 65 |
Feb. 16.| | | | | |
A.M. 4. |N. W. | 3 |q. |30.18| 62 |
P.M. 8. | N. N. W. | 2 | c. g. |30.21| 66 |
------------------------------------------------------------------------
b. indicates blue sky--c. detached clouds--r. rain--v. visibility of
objects--q. squalls--w. wet dew--u. ugly threatening appearance--g.
gloomy weather.
The exact counterpart of the first norther may be observed with us every
fall. On the 30th January, with a rising thermometer and falling
barometer, there was rain at midday. The night following was moist--the
next day, about ten A.M., the wind came out N. W., with squalls and gloomy
weather, a falling thermometer, and rising barometer.
The norther of Feb. 14th differed from the other only in regard to the
time of the day when it commenced; the order of events was the same. The
rain fell in the night--it cleared off early in the day, and the norther
followed in the afternoon. This also is frequently the case with us, as
every one may observe.
This brief notice of the surface winds of our climate would be incomplete
without a description of those of the thunder-gust and tornado.
The former is exceedingly simple. The showers, which are accompanied with
much wind, form suddenly in hot weather, and have a considerable advance
condensation (frequently with obvious lateral internal action), extending
eastwardly from the line of smooth cloud from which the rain is falling,
or rather where the falling rain obscures the inequalities of the cloud.
_The gust is never felt until the advancing condensation has passed over
us_, when it takes the place of the gentle easterly breeze which
previously set toward the shower. _The gust ceases as soon as the cloud
has passed._ It is obviously the result of the inducing and attracting
influence of the cloud upon the atmosphere near the surface of the earth
as it passes over it. Let the reader watch attentively this advance
condensation, from its eastern edge to the line of smooth cloud and
falling rain, and he will understand at a glance this internal action of
gust-clouds. The whole phenomena are simple and intelligible. A cloud
approaching from a westerly point, dark and irregular from its eastern
edge to the line of falling rain, where it appears smooth and of a light
color; wind from the east blowing gently toward it, till the condensation
is over us; then the gust following the cloud; then the rain, and in a few
minutes the cloud, and wind, and rain have passed on to the east, and
"sunshine" returns.
The tornado, as it is termed when it occurs upon land, "spout," if on the
water, is sometimes of a different character, and as it undoubtedly had
great influence in inducing the gyrating theory of Mr. Redfield, and the
aspiratory theory of Mr. Espy, and has been cited by both in support of
their respective theories, it deserves a more particular notice. There are
several marked peculiarities attending it which determine its character.
1st. It occurs during a _peculiarly sultry and electric_ state of the
trade and surface atmosphere, and at a time when thunder showers are
prevailing in and around the locality, and at every period of the year
when such a state of the atmosphere exists. One recently occurred in
Brandon, Ohio, in midwinter.
2d. There is always a cloud above, but very near the earth, between which
and the earth the tornado forms and rages. It is usually described as a
black cloud, ranging about 1000 feet or less above the earth, often with
a whitish shaped cone projecting from it, and forming a connection with
the earth; at intervals rising and breaking the connection, and again
descending and renewing it with devastating energy. Its width at the
surface varies from forty to one hundred and eighty rods--the most usual
width being from sixty to ninety rods. Sometimes when still wider, they
have more the character of thunder-gusts, and are brightly luminous.
3d. Two motions are usually visible, one ascending one near the earth and
in the middle, and a gyratory one around the other. The latter is rarely
felt, or its effects observed, near the earth. Occasionally, and at
intervals, objects are thrown obliquely backward by it.
4th. It is composed, at the surface of the earth, of _two lateral
currents_, a northerly and southerly one, varying in direction, but
normally at right angles in most cases, although not always, with its
course of progression, extending from the extreme limits of its track to
the axis; which currents are most distinctly defined toward the center,
and upward. These currents prostrate trees, or elevate and remove every
thing in their way which is detached and movable. There does not seem to
be any current in advance of these lateral ones tending toward the
tornado, save in rare and excepted cases, and then owing to the make of
the ground or the irregular action of the currents; nor any following,
except that made by the curving of the lateral currents toward the center
of the spout as it moves on, and perhaps a tendency of the air to follow
and supply the place of that which has been carried upward and forward,
like that of water following the stern of a vessel. The south current is
always the strongest, and often a little in advance of the other, and
covers the greatest area. The proportion of the two currents to each other
is much the same that the S. E. trades bear to the N. E. This excess in
volume and strength of the southerly current will explain the
irregularities in most cases, and the fact that objects are so often
_taken up and carried from the south to the north side_, and so rarely
from the north and carried south of the axis. These irregularities are
such as attend all violent forces, and something can be found which will
favor almost any theory; but the two lateral currents appear always to be
the principal actors, except, perhaps, when it widens out and assumes more
the character of a straightforward gust. See a collection by Professor
Loomis, American Journal of Science, vol. xliii. p. 278.
The following diagram is a section of the New Haven tornado, from
Professor Olmstead's map accompanying his article in the "American Journal
of Science and Art," vol. 37. p. 340.
The manner in which the main currents flow is shown by their early and
unresisted effect in a cornfield, as represented by the dotted lines. The
direction in which the fragments of buildings were carried by the greater
power of the southerly currents is shown also. And so is this irregular
action, where a part of the southerly current broke through the northerly
one, and prostrated two or three trees backward on the north side of the
axis.
[Illustration: Fig. 16.]
5th. This cloud, and its spout, move generally with the course of the
counter-trade in the locality--_i. e._, from some point between S. W. and
W., to the eastward, but occasionally a little south of east, deflected by
the magnetic wave beneath the belt of showers.
6th. Several exceedingly instructive particulars have been observed and
recorded.
_a_. _No wind is felt outside of the track_, as those assert who have
stood very near it, and its effects show.
_b_. The track is often as distinctly marked, where it passed through a
wood, as if the grubbers had been there with their axes to open a path for
a rail-road. The branches of the trees, projecting within its limits, are
found twisted and broken off, or stripped of their leaves, while not a
leaf is disturbed at the distance of a foot or two on the opposite side of
the tree, and outside of the track.
_c_. As the spout passes over water, the latter seems to _boil up_ and
_rise to meet it_, and _flow up_ its trunk in a _continued stream_.
_d_. As it passes over the land, and over buildings, fences, and other
movable things, they appear to _shoot up_, instantaneously, as it were,
into the air, and into fragments. If buildings are not destroyed or
removed, the doors may be burst open _on the leeward side_, and gable ends
_snatched out_, and roofs taken off on the _same side_, while that portion
of the building which is to the windward remains unaffected.
_e_. Articles of clothing, and other light articles, have been carried out
of buildings through open doors, or chimneys, or holes made in the roofs,
and to a great distance, without _any opening_ being made for the air to
_blow_ in.
_f_. If there be a discharge of electricity up the spout from the earth,
like that of lightning, the intense action ceases for a time or entirely.
_g_. Vegetation in the track is often scorched and killed, and so of the
leaves on one side of a tree, which is within the track, while those on
the other side, and without the track remain unaffected. (Espy's
Philosophy of Storms, 359, cited from Peltier.)
_h_. The active agent whatever it is, has been known to _seize hold of a
chain attached to a plow_ and _draw the plow about, turning the stiff sod
for a considerable distance_. (See Loomis on the tornado at Stow, Ohio,
American Journal of Science, vol. xxxiii. p. 368.)
_i_. In passing over ponds, the spout has taken up all the water and fish,
and scattered them in every direction, and to a great distance.
_j_. The barometer falls very little during the passage of the spout. (See
the Natchez hurricane of 1827, Espy page 337.) Not more than it
_frequently_ does during gentle showers.
_k_. Persons have been taken up, carried some distance, and if not
projected against some object in the way, or some object against them,
have usually been _set down gently and uninjured_.
_l_. Buildings which stood upon posts, with a free passage for the air
under them, although in the path of the tornado, escaped undisturbed.
(Olmstead's account of the New Haven tornado, American Journal of Science,
vol. xxxvii. p 340.)
_m_. A chisel taken from a chest of tools, and stuck fast in the wall of
the house. (Ibid.)
_n_. Fowls have had all their feathers stripped from them in an instant
and run about naked but uninjured.[5]
_o_. Articles of furniture, etc., have been found torn in pieces by
antagonistic forces.
_p_. Frames taken from looking-glasses without breaking the glass. Nails
drawn from the roofs of houses without disturbing the tiles.
_q_. Hinges taken from doors--_mud taken from the bed of a stream_ (the
water being first removed), and let down on a house covering it
completely--a farmer taken up from his wagon and carried thirty rods, his
horses carried an equal distance in another direction, _the harness
stripped from them_, and the wagon carried off also, _one wheel not found
at all_. (American Journal of Science, vol. xxxvii. p. 93.)
Pieces of timber, boards, and clapboard, driven into the side of a hill,
_as no force of powder could drive them, etc., etc._
Now to my mind, these circumstances indicate clearly, that it is not wind,
_i. e._, mere currents of air, which produces the effect, but that a
_continuous current_ or _stream of electricity_ from the earth to the
cloud exists, and carries with it from near the earth, such articles as
are movable: That this stream collects from the _northerly_ and
_southerly_ side upon the _magnetic meridian_, in _two currents_ with
_polarity_, which meet in their passage up at the center; curving toward
the center in the posterior part as the spout moves on, when acting in a
normal manner, and making the "_law of curvature_" observed: That no
conceivable movement of the air alone in such limited spaces could produce
such effects; or if so, that no agent but electricity could so move the
air: That the air in a building could not shoot the roof upward, and into
fragments; much less could the air in a cellar by any conceivable force,
be made to elevate _or shoot up_ the entire house, and its inmates, and
contents--effects so totally unlike what takes place in gales,
hurricanes, and typhoons: That elastic free air never did nor could take
hold of the plow chain, and plow up the ground; or scorch and kill the
vegetation; or twist the _limbs_ from one side of a tree, while the most
delicate leaves on the other, and within two or three feet, remained
unaffected and undisturbed; or pick the chickens: That even if the
expansion of the air could produce these effects--if a sudden vacuum were
produced--_nothing but currents of electricity could produce the sudden
vacuum_, by removing the air above.
It is well settled that atmospheric electricity can and does flow in
currents with light, by experiments in relation to the brush discharge,
etc. That it may do so without light or disruptive discharge, and in a
stream, or as it is termed, by convection, with the force and effect seen
in the tornado, is perfectly consistent with what we know of it--and it
is, I think clearly evinced that such is the character of the phenomena,
by the fact that a sudden powerful _disruptive_ discharge, _with light, up
the spout_, produces an instantaneous partial or total suspension of its
action; to be renewed as the cloud passes over _another_ and more highly
charged _portion_ of the _earth's surface_. Peltier gives instances where
the spout has been entirely and instantaneously destroyed by such a sudden
and powerful discharge of electricity; marking the spot where it was so
destroyed by a large hole in the earth, from which the discharge issued.
And in fact these tornados are often steadily luminous, and so much so,
when they occur in the night, as to enable persons to read without
difficulty.
The lateral inward and upward currents, are accompanied, after they meet
and unite, or seem to unite, by gyratory or circular ones. How are they
produced? This question can only be answered by analogy. No permanent
impressions are left by the circular currents, except to a limited extent,
and in occasional instances; and observation of them has been, and must
necessarily be limited and uncertain. I have witnessed one or two on a
moderate scale; but owing to the suddenness of their passage, and the
confusion of the objects taken up, it was difficult to determine what the
circular currents were. When the southerly current is much the strongest,
it appears sometimes to cross the axis, and curve round the northerly one.
Perhaps this may be all the curving that really takes place, except at the
posterior part of the axis, for evidence of a curving on the south of the
axis is rarely, if ever seen.
Assuming, however, that the main currents unite and form one from the
earth to the cloud, _induced_ circular currents would be in perfect
keeping with the known laws of electricity. Such currents, and with
magnetic properties, are always induced by powerful currents of voltaic
electricity passing through wires. And doubtless _in all cases_ powerful
currents of electricity _induce attendant circular currents_. This may
account for the external gyration of the spout.
Or it may be that the two lateral currents of air which attend the
currents of electricity, do not unite; having opposite polarity, but pass
by and around each other, in connection with the circular magnetic
currents. Future observation and perhaps experimental research will
determine this. But it may not be accomplished by the present generation;
for the belief that tornados are mere whirlwinds, produced by the action
of the sun in heating the land, is adhered to, notwithstanding they cross
the intense magnetic area of Ohio in mid-winter, and seems to be
ineradicable.
The proportions of different winds vary in different localities. For the
benefit of those who are curious, I copy a table from an able compilation
by Professor Coffin, published by the Smithsonian Institute, showing the
proportion of the winds at New Haven (the station nearest to me). It will
be noticed that during the year the N. W. winds blow the greatest number
of days; the S. W. next; the N. E. and S. E. less than either, and about
equal. It may be observed that the two latter bear about the same
proportion to the whole, that our number of cloudy and stormy days,
averaging about ninety, bear to the whole number of days in the year.
+------------------------------------------------+
|Course.| 1804. | 1811. | 1812. | 1813. | Total. |
|------------------------------------------------|
| N. | 143 | 105 | 90 | 111 | 449 |
| N. E. | 99 | 207 | 138 | 138 | 582 |
| E. | 33 | 18 | 22 | 23 | 96 |
| S. E. | 131 | 108 | 135 | 110 | 484 |
| S. | 58 | 69 | 113 | 80 | 320 |
| S. W. | 224 | 255 | 153 | 261 | 893 |
| W. | 81 | 69 | 102 | 57 | 309 |
| N. W. | 329 | 264 | 345 | 315 | 1253 |
+------------------------------------------------+
This work of Mr. Coffin has been brought to my notice since the foregoing
pages were written. The facts embodied in it will be found to comport with
what I have observed and stated. In relation to the proportionate number
of days in the year during which the wind blows from the different points
of the compass at the several stations it is very full and able.
But it has cardinal defects. It does not show the _main currents_ of the
atmosphere. It treats the surface-winds, which are incidental, as
principals. The direction of the main currents is indeed shown frequently
by the mean course of the surface winds, but not uniformly or
intelligibly. Nor does it distinguish between the fair weather and storm
winds; nor always between the trade winds during their northern transit,
and the variable winds north of the trade-wind region. Hence, the
deductions derived from it disclose no general system, and sustain no
theory, although many very important facts appear. Some of these,
Professor Coffin found it difficult to reconcile with received theories,
or satisfactorily explain. For instance, he found the prevailing winds of
the United States, in Louisiana and Texas, S. and S. E.; in western
Arkansas, and Missouri, southerly, and in Iowa and Wisconsin, S. W.,
forming a curve, and evidently connected together.
Thus, alluding to the winds west of the Mississippi, and between the
parallels of 36 deg. and 60 deg., he says:
"On the American continent, west of the Mississippi, there appears to
be more diversity in the mean direction of the wind, yet here it is
westerly at sixteen stations out of twenty, from which observations
have been obtained. The most peculiar feature in this region, is the
_line_ of southerly winds on the western borders of Arkansas and
Missouri. It seems to form a connecting link between the winds of
this zone and the south-easterly ones that we find south of it; and,
in some degree, to favor an idea that has been advanced, that there
is a vast eddy, extending from the western shore of the Gulf of
Mexico, to the eastern shore of the Atlantic; that the easterly
trade-winds of the Atlantic Ocean, when they strike the American
continent, veer northwardly, and then N. E., and thus recross the
Atlantic, and follow down the coast of Portugal and Africa, till they
complete the circuit."
This mean prevalence of the curving winds indicates the course of the
western portion of the concentrated counter-trade, of which we have so
fully spoken, and to which that portion owes its rains and fertility.
Doubtless the curve would have been traced somewhat further west, if
observations had been obtained from more westerly stations.
The idea of an eddy, to which Professor Coffin alludes, is of course
unsound; that of a counter-trade, most fully confirmed; the curve
corresponding with that of the regular rains and fertility as they are
known to exist.
Professor Coffin is a believer in the generally-received theory of
rarefaction, as the cause of all winds. His work is published by the
Smithsonian Institution, and the theory is, so far forth, nationalized.
But he found it very difficult to reconcile all the facts he obtained,
with the theory, and, possessing a truth-loving mind, he frankly admits
it. Alluding to the prevalence of N. E. winds off the coast of Africa in
the summer months, as shown by certain numbered wind-roses, he says:
"Nos. 81, 83, 86, and 91, have caused me much perplexity. The arrows
for the warmer months evidently indicate a point of rarefaction
situated to the _south_ or _south-west_, and yet all the observations
from which they were computed were taken within a few hundred miles
of the African coast and desert of Sahara; a region, the annual range
of whose temperature must be exceedingly great. The only way in which
I can account for a fact so astonishing, is, by supposing the
deflecting forces at these numbers to be secondary to the influence
which we see so strongly marked in Nos. 88, 89, and 90. Let us, then,
first devote our attention to these."
(We have not space for the map of Professor Coffin, nor is it necessary to
insert it. The numbers 81, 83, 86, and 91, refer to respective portions of
the Atlantic, west of Africa, North of the Cape de Verdes, of 5 deg. of
latitude each, where the N. E. trades are drawing off from the coast. The
Nos. 88, 89, and 90 refer to like portions _below_ the Cape de Verde,
where the S. W. monsoons are found under the rainy belt; and the
explanation of the distinguished author is an attempt to account for the
blowing of the trades _from_ Sahara, by supposing them connected with the
monsoons further south, which seem to blow toward it.)
"The intense heat of the Great Desert rarefies the air exceedingly
from June to October, inclusive, and hence the arrows of unparalleled
length (Plate XII.)," (showing the monsoon winds below the Cape de
Verdes,) "pointing toward it during those months, the longest being
longer than that which represents the most uniform of the
trade-winds, in the ratio of 104 to 89. The influence of this
rarefaction is sufficient to curve the powerful current of the
trade-winds in the manner exhibited on Plate VII. Nos. 89 and 90, and
to produce the not less remarkable change in No. 88, holding the
current back and retarding it, so that its progressive motion in the
_three_ months of July, August, and September united, hardly exceeds
that during any _one_ of the colder months of the year. But while
this is so, the trades on the western side of the Atlantic are
pursuing nearly their regular track, being but slightly affected by
these influences. As a consequence, the latter must leave, as it
were, a partial vacuum behind them, which is filled by air flowing in
from the north-east and south-east. This will account for the seeming
anomaly of having a somewhat strong deflecting force directed toward
mid-ocean, in the hottest part of the year, as in the numbers above
referred to. _And yet it may be very naturally asked, Why does not
the air from these parts supply the Great Desert directly, instead of
taking a circuitous route to supply the region that supplies it? A
question which, I confess, it seems difficult to answer._"
(The italicization in the foregoing extract is mine).
Here the worthy professor finds a fact inconsistent with the theory of
rarefaction--viz.: that the winds blow off shore, and toward mid-ocean,
opposite Sahara, and he is "perplexed and astonished." The theory,
however, must be maintained, and one of those modifying hypotheses which
have made meteorology such a complicated piece of patch-work, must be
invented; some "deflecting forces" found. There is the Great Desert,
bordering upon the ocean, north of the Cape de Verde Islands, for a
distance of six hundred miles, widening as it extends inland, whose
temperature, as he says, "_must be exceedingly great_;" and doubtless is
so, and yet the air, instead of blowing in upon it in a hurricane, is
actually drawing off from it, and blowing towards the S. W., where the
water and air do not rise above 84 deg.. Well may he be "perplexed and
astonished."
Turning south, however, to the distance of five hundred miles or more, he
finds the S. W. monsoon winds, which in those months blow under the belt
of rains, toward the land, in the direction of, but at a great distance
from, Sahara. It is an easy matter to suppose that they reach the Great
Desert and supply its vortex of rarefaction, inasmuch as they blow in a
direction toward it, and distance is no impediment to supposition.
Then it is necessary to _suppose_ that the S. E. and N. E. trades, at the
south-west, draw so strongly to the westward as to create a partial vacuum
to the S. W. of Sahara, which is filled by the winds which draw off shore,
and then we have the supply brought from the distance of five hundred
miles or more, by an ascending vortex, which creates a vacuum, and the air
near the vortex taken away in _another_ direction by a _partial_ vacuum;
and so an ascending _vortex_, which creates a vacuum is supplied from a
distance, and a _partial vacuum_ at a distance is supplied by the air near
the perfect vacuum. Such an idea of a supply by a circuitous route, and
secondary influence, is not very philosophical, to say the least, and
Professor Coffin feels it; and to the question, Why is it so? which, he
says, may very naturally be asked, he confesses there is no answer. And
there would be none, even if his suppositions were based upon facts. But
other questions might be asked equally difficult to be answered, viz.:
1st. Is there any rarefaction which can draw the trades to the west, and
in that particular locality, in opposition to the supposed vortex of
Sahara, by creating a _partial vacuum_?
2d. Are they in fact so drawn?
3d. Do the S. W. winds, south of the Cape de Verdes, and _under the rainy
belt_, which in the summer months extend up to these islands, _reach the
desert at all_?
These are pertinent questions, _and every one of them must be answered in
the negative_. The hypothesis is without foundation, and Professor's
Coffin's perplexity and astonishment must remain, until he abandons the
theory of rarefaction entirely. The winds which so perplex him are nothing
but the regular N. E. trades, made to originate on the coast and continent
of Africa, in summer, by the northern transit of the whole machinery. They
not only draw off from the desert coast, but they _blow over the desert
itself_ on to the ocean, and into the rainy belt upon the land, as we have
already seen, and the supposed vortex of rarefaction does not exist.
That the monsoons do not reach the desert is demonstrated by the tables of
Professor Coffin, and to set it at rest we will make the necessary
extracts. Commencing with the region from the equator to 5 deg. N., and from
10 deg. to 55 deg. W. longitude, we have the observed winds in proportion, as
follows, for July and August--the south-east trades prevailing, inasmuch
as the belt of rains is at this season situated further north.
LATITUDE 0 deg. TO 5 deg., LONGITUDE FROM GREENWICH 10 deg. TO 55 deg..
+-------------------------------------------------------+
| Course. | July. | August. | Course. | July. | August. |
|-------------------------------------------------------|
| North. | 0 | 0 | S. S. W.| 54 | 111 |
| N. N. E.| 8 | 2 | S. W. | 1 | 29 |
| N. E. | 6 | 2 | W. S. W.| 6 | 19 |
| E. N. E.| 27 | 16 | West. | 2 | 9 |
| East. | 31 | 20 | W. N. W.| 1 | 6 |
| E. S. E.| 120 | 96 | N. W. | 1 | 0 |
| S. E. | 216 | 276 | N. N. W.| 0 | 2 |
| S. S. E.| 218 | 443 | Calm. | 8 | 4 |
| South. | 69 | 279 |---------------------------|
| | | | Total | 768 | 1,314 |
+-------------------------------------------------------+
Here, it is evident that the S. E. trades are the prevailing winds, but
their course is variable.
Ascending to the region between 5 deg. and 10 deg. north latitude, and 10 deg. to 55 deg.
west longitude, the northern part of which at this season is covered by
the rainy belt; we find the monsoon, the S., S. S. W., and S. W. winds,
the prevailing ones in August, although the winds are variable, as usual
under the rainy belt.
+-------------------------------------------------------+
| Course. | July. | August. | Course. | July. | August. |
|-------------------------------------------------------|
| North. | 19 | 6 | S. S. W.| 188 | 368 |
| N. N. E.| 26 | 11 | S. W. | 63 | 94 |
| N. E. | 104 | 32 | W. S. W.| 73 | 93 |
| E. N. E.| 30 | 16 | West. | 33 | 48 |
| East. | 45 | 29 | W. N. W.| 30 | 18 |
| E. S. E.| 36 | 40 | N. W. | 21 | 9 |
| S. E. | 93 | 53 | N. N. W.| 17 | 13 |
| S. S. E.| 225 | 307 | Calm. | 109 | 74 |
| South. | 239 | 514 |---------|-------|---------|
| | | | Total | 1,351 | 1,725 |
+-------------------------------------------------------+
Ascending to the region of 10 deg. to 15 deg. north latitude, and 15 deg. to 45 deg. west
longitude, we find the winds exceedingly variable, and the monsoons
diminished remarkably. If Professor Coffin's theory was correct, they
should increase as they approach the desert; but they in fact, diminish,
and the N. E. trades are found at the north portion.
+-------------------------------------------------------+
| Course. | July. | August. | Course. | July. | August. |
|-------------------------------------------------------|
| North. | 17 | 55 | S. S. W.| 30 | 71 |
| N. N. E.| 64 | 74 | S. W. | 33 | 63 |
| N. E. | 155 | 149 | W. S. W.| 19 | 43 |
| E. N. E.| 91 | 71 | West. | 12 | 25 |
| East. | 83 | 60 | W. N. W.| 17 | 21 |
| E. S. E.| 25 | 26 | N. W. | 13 | 24 |
| S. E. | 17 | 26 | N. N. W.| 24 | 56 |
| S. S. E.| 13 | 33 | Calm. | 62 | 78 |
| South. | 9 | 44 |---------|-------|---------|
| | | | Total | 684 | 919 |
+-------------------------------------------------------+
Ascending to the region between 15 deg. and 20 deg. north latitude, and 15 deg. to 45 deg.
west longitude, we get north of the belt of rains _and lose the monsoons
entirely although still below the desert_; and find the regular N. E.
trades, with less variable winds than are found in almost any other part
of the ocean.
+-------------------------------------------------------+
| Course. | July. | August. | Course. | July. | August. |
|-------------------------------------------------------|
| North. | 39 | 20 | S. S. W.| 0 | 5 |
| N. N. E.| 210 | 185 | S. W. | 0 | 5 |
| N. E. | 112 | 87 | W. S. W.| 8 | 3 |
| E. N. E.| 114 | 104 | West. | 0 | 1 |
| East. | 20 | 36 | W. N. W.| 0 | 4 |
| E. S. E.| 21 | 17 | N. W. | 3 | 4 |
| S. E. | 0 | 2 | N. N. W.| 3 | 31 |
| S. S. E.| 2 | 11 | Calm | 20 | 8 |
| South. | 5 | 1 |---------|-------|---------|
| | | | Total, | 557 | 526 |
+-------------------------------------------------------+
Ascending still further to the region between 20 deg. and 25 deg. north latitude,
and 15 deg. and 45 deg. west longitude, which borders, in part, on the S. W.
corner of the desert, and we have not, during the month of August, a
single wind between S. S. E. and W. N. W., which blows in upon the land;
and _only twelve instances out of three hundred and ninety-four in this
hottest month in the year, and on the southern portion of the desert, when
the wind blows on shore from any quarter_. This is demonstration. The
monsoon winds are confined to the rainy belt; they do not reach the
desert, nor does the desert attract the winds from the ocean, or
reverse, hold back, or disturb the trades.
+-------------------------------------------------------+
| Course. | July. | August. | Course. | July. | August. |
|-------------------------------------------------------|
| North. | 25 | 20 | S. S. W.| 3 | 0 |
| N. N. E.| 210 | 153 | S. W. | 2 | 0 |
| N. E. | 129 | 77 | W. S. W.| 13 | 0 |
| E. N. E.| 110 | 86 | West. | 0 | 0 |
| East. | 8 | 20 | W. N. W.| 0 | 3 |
| E. S. E.| 4 | 11 | N. W. | 2 | 1 |
| S. E. | 0 | 3 | N. N. W.| 5 | 8 |
| S. S. E.| 1 | 7 | Calm. | 2 | 5 |
| South. | 1 | 0 |---------|-------|---------|
| | | | Total, | 515 | 394 |
+-------------------------------------------------------+
Ascending once more, to the region between the degrees of 25 and 30, north
latitude, and 15 and 45, west longitude, we find it bounded east entirely
on the center of the desert. Now here, certainly, there must be evidence
of the truth of the rarefaction theory, if any where on the face of the
earth. Yet here, in July and August, we find the trades as regular as any
where, and not more variable winds than are found in the trades toward
their northern limits every where, and in August, only forty out of four
hundred and twenty-nine winds, blowing directly or indirectly on shore.
+-------------------------------------------------------+
| Course. | July. | August. | Course. | July. | August. |
|-------------------------------------------------------|
| North. | 32 | 19 | S. S. W.| 9 | 6 |
| N. N. E.| 155 | 125 | S. W. | 3 | 9 |
| N. E. | 144 | 35 | W. S. W.| 13 | 14 |
| E. N. E.| 140 | 89 | West. | 12 | 3 |
| East. | 48 | 57 | W. N. W.| 7 | 7 |
| E. S. E.| 31 | 23 | N. W. | 11 | 1 |
| S. E. | 8 | 7 | N. N. W.| 36 | 6 |
| S. S. E.| 8 | 12 | Calm. | 18 | 12 |
| South. | 5 | 4 |---------|-------|---------|
| | | | Total, | 680 | 429 |
+-------------------------------------------------------+
It would seem to be impossible for any man to believe in the theory of
rarefaction, after an examination of these tables.
Professor Coffin discovers other anomalies, for which he finds it
difficult to account. Among these are the northerly tendency, in the
afternoon, of the winds in Ohio, south of Lake Erie; the winds of
south-western Asia, which, he says, "Are so irregular as to defy all
attempts to reduce them to system;" particularizing the N. W. at
Jerusalem, the westerly at Bagdad, the N. E. at Constantinople, the
northerly at Trebizond, etc., etc. Jerusalem has the Mediterranean at the
N. W., Bagdad has it at the west, Constantinople has the Black Sea at the
N. E., Trebizond N. N. W. and N. E., and the counter-trade, as it passes
over them, draws its storm-surface wind or sea-breeze, from the quarter
where evaporation is greatest, and the atmosphere is most susceptible of
electrical inductive influence. Precisely as it draws from the ocean and
the eastward, east of the Alleghanies, from the lake region, west of the
lakes, and from the northward, south of the lakes, and from the westward,
east of them.
This law of attraction will explain, too, the mean prevalence of easterly
winds north of the parallel of 60 deg., at the stations named in his work.
Great Bear Lake, Great Slave Lake, and Fort Enterprise, lie east of the
Rocky Mountain range which interposes between them and the Pacific, and
have Hudson's Bay and other large bodies of water on the east and north.
Hence, easterly winds prevail at these places. At Norway House, on
Nelson's River, near the north end of Lake Winnipeg, a large body of
water, which stretches off to the south, we find the south wind the
prevalent one, especially in December, when the northern and north-eastern
waters are frozen up, and the N. E. largely present at all seasons of the
year.
At New Hernhut, in winter, when Davis' Straits are covered with floes, the
prevailing wind is east, drawn from the warm, open sea east of Greenland,
where the Gulf Stream is evaporating. But in June and July, when
evaporation is going on over Davis' Straits and Baffin's Bay, the
prevailing winds are west and south, and the east winds fall off.
Other stations are equally instructive, but I must forbear.
In relation, however, to the easterly zone of wind, of which Professor
Coffin speaks, it should be added that the counter-trade, south of the
magnetic pole, in high latitudes, pursues an easterly course, is near the
earth, and attracts an opposite wind as it does on the east and north of
the pole, in localities where the surface atmosphere is not peculiarly
susceptible to its influence, and, therefore, the _winds are mainly
opposite to its course_. Thus, at Melville Island, they are almost all
westerly and north-westerly, for there the remnant of the counter-trade is
passing west around the magnetic pole. These westerly and north-westerly
winds are very light, and like the gentle easterly breeze which sets
toward the cumulus clouds and summer showers.
Since most of this work was written, I have procured, and read with great
pleasure, Lieutenant Maury's "Geography of the Sea." It is a work of
great interest, and should be in the hands of every one. The extent of
ground covered, however, made it necessary for Lieutenant Maury to
introduce much matter not derived from his own investigations. In doing
this, he has taken received opinions, and has thereby introduced much
heresy. The view he adopts in relation to the monsoons, although the
popular one with philosophers, is of that character. He says (page 222):
"Monsoons are, for the most part, formed of trade-winds. When a
trade-wind is turned back, or diverted, by over-heated districts,
from its regular course at stated seasons of the year, it is regarded
as a monsoon. Thus, the African monsoons of the Atlantic, the
monsoons of the Gulf of Mexico, and the Central American monsoons of
the Pacific, are, for the most part, formed of the north-east
trade-winds, which are turned back to restore the equilibrium which
the over-heated plains of Africa, Utah, Texas, and New Mexico have
disturbed. When the monsoons prevail for five months at a time--for
it takes about a month for them to change and become settled--then
both they and the trade-winds, of which they are formed, are called
monsoons."
Again (Sec. 476-7):
"The agents which produce monsoons reside on the land. These winds
are caused by the rarefaction of the air over large districts of
country situated on the polar edge, or near the polar edge, of the
trade-winds. Thus, the monsoons of the Indian Ocean are caused by the
intense heat which the rays of a cloudless sun produce, during the
summer time, upon the Desert of Cobi and the burning plains of
Central Asia. When the sun is north of the equator, the force of his
rays, beating down upon these wide and thirsty plains, is such as to
cause the vast superincumbent body of air to expand and ascend. There
is, consequently, a rush of air, especially from toward the equator,
to restore the equilibrium; and, in this case, the force which tends
to draw the north-east trade-winds back becomes greater than the
force which is acting to propel them forward. Consequently, they obey
the stronger power, turn back, and become the famous south-west
monsoons of the Indian Ocean, which blow from May to September
inclusive.
"Of course, the vast plains of Asia are not brought up to monsoon
heat _per saltum_, or in a day. They require time both to be heated
up to this point and to be cooled down again. Hence, there is a
conflict for a few weeks about the change of the monsoon, when
neither the trade wind nor the monsoon force has fairly lost or
gained the ascendency. This debatable period amounts to about a month
at each change. So that the monsoons of the Indian Ocean prevail
really for about five months each way, viz.: from May to September,
from the south-west, in obedience to the influence of the over-heated
plains, and from November to March inclusive from the north-east, in
obedience to the trade-wind force."
What the "trade-wind force" is, Lieutenant Maury tells us in another
paragraph, viz.: "Calorific action of the sun and diurnal rotation of the
earth"--the received calorific theory. I have already shown, I think,
conclusively, that there is no expansion and ascent in the supposed region
of calms, which induces, or can induce, the trades; and that, in point of
fact, the air on the land is cooler under the belt of rains. But as
Lieutenant Maury, whose reputation is national, adopts the theory, I shall
be pardoned for copying the following table, showing the difference of
temperature at two cities of India, before, after, and while the belt of
inter-tropical rains is over them. It will be seen that the temperature is
actually less when the belt is there, viz., in July and August, than in
April and May. _This should be conclusive upon that point._
+----------------------------------------------------+
| | Anjarakandy. | Calcutta. |
| Months. |--------------------|-------------------|
| | Rain. | Temp. | Rain. | Temp. |
|-----------|----------|---------|---------|---------|
| | M. M. | | M. M.| |
| January, | 2,26 | 26 deg.,5 | 0,0 | 18 deg.,4 |
| February, | 2,26 | 27 deg.,7 | 67,68 | 21 deg.,5 |
| March, | 6,77 | 28 deg.,4 | 24,82 | 25 deg.,6 |
| April, | 29,33 | 29 deg.,8 | 130,84 | 28 deg.,5 |
| May, | 175,96 | 28 deg.,6 | 16,24 | 29 deg.,7 |
| June, | 794,05 | 26 deg.,6 | 575,24 | 29 deg.,3 |
| July, | 807,59 | 25 deg.,8 | 338,38 | 28, deg.1 |
| August, | 572,98 | 26 deg.,0 | 311,31 | 28 deg.,3 |
| September,| 311,31 | 26 deg.,4 | 254,91 | 28 deg.,0 |
| October, | 157,91 | 26 deg.,8 | 42,86 | 27 deg.,2 |
| November, | 65,42 | 26 deg.,9 | 20,30 | 23 deg.,0 |
| December, | 29,33 | 26 deg.,5 | 0,0 | 19 deg.,2 |
|-----------|----------|---------|---------|---------|
| Year, | 2955,14 | 27 deg.,2 | 1928,74 | 26 deg.,4 |
+----------------------------------------------------+
Anjarakandy is on the Malabar coast, between 12 deg. and 13 deg. north latitude.
Calcutta in an angle of the Bay of Bengal, at 22 deg. 30' north latitude. The
former is in and near the focus of the monsoons, and has a temperature in
July (when 18 inches of rain fall), about as low as in December.
In the foregoing table from Kaemptz, the rain is in millimetres, about
twenty-five of which make an inch, and the temperature is centigrade,
which may be raised to Fahrenheit by adding four fifths of the quantity
and also 32 deg.--thus, if the height of the centigrade thermometer be 25 deg.,
add to this four fifths of 25 deg., which is 20 deg., and also 32 deg., the result is
77 deg.. Twenty-five centigrade is therefore equal to seventy-seven
Fahrenheit.
Lieutenant Maury is not, and should not be a theorist. He occupies the
position, in some sort, of a national _investigator_, and, of course, of
national _instructor_. Opinions which emanate from him, or which are
endorsed by him, should be accurate. Sooner or later that which he has
adopted in relation to the monsoons, and some others, must be abandoned.
In addition to what has already been said, I wish to call his, and the
reader's attention, to several other facts and considerations in relation
to the monsoons, and particularly those of India.
1st. The deserts of Cobi and Bucharia, which constitute the "burning
plains" of _Central_ Asia, north-east of the Indian Ocean, lie between 38 deg.
and 45 deg. of north latitude, and under the zone of extra-tropical rains.
They are not wholly rainless. They partake of that saline character which
affects so much of Asia and the western part of this continent. South of
them, running nearly east and west, are the lofty ranges of the Himmalaya
and Kuenlun Mountains, and the table lands of Thibet. To their saline
character, in part, but mainly to the interposition of these mountain
ranges, depriving the counter-trade of moisture, they owe their
comparative sterility. _If bountifully supplied with rains, this salt
would doubtless ere this have been washed to the ocean, as it has been
from other countries, once as salt as they._ But they have some rain, and
more or less vegetation, and are not intensely hot. They lie too far
north, and are too elevated. Their temperature is not materially different
from that of the western, and comparatively desert portions of our own
country, and they are utterly incapable of creating a monsoon at the
Indian Ocean, and especially from the long line of Malabar coast, where
the south-west monsoons are found in most strength. The sterile portions
of Utah, New Mexico, and Texas are alike incapable of such effect upon the
atmosphere of Central America and Mexico. These monsoons commence in May,
and prevail until October, and the temperature of the air where they blow
ranges with considerable regularity between 76 deg. at night, and 84 deg. at
mid-day, on the Malabar coast, and a trifle lower in Central America.
At Fort Fillmore, El Paso, New Mexico, in latitude 32 deg.03, the mean
temperature for
May is 68 deg.
June " 78 deg., 5'
July " 80 deg., 1'
August " 83 deg., 8'
September " 77 deg., 9'
-------
And for the whole period, 77 deg., 1'
At Santa Fe, New Mexico, the mean for
May is 66 deg., 9'
June " 72 deg., 5'
July " 75 deg., 3'
August " 72 deg., 9'
September " 62 deg., 3'
-------
And for the whole period, 69 deg., 3'
Mean of the two united, 73 deg., 2'
The mean of Western Texas is about 2 deg. higher than at Fort Fillmore, and of
Utah not materially different; and the mean of _Central_ Asia between 38 deg.
and 45 deg. does not materially vary from them.
Now, it is perfectly evident that during May and September the temperature
of Central Asia is far below that of the Indian Ocean and India, and never
materially exceeds it. Central Asia is hot, "burning," if you please,
compared with more elevated, fertile, or better watered territory _in the
same latitude_, and so it has been characterized; but not so, compared
with the Indian Ocean, or India, where the sun is vertical. During the
greater part of the time, therefore, that the monsoons are in full blast,
Utah, Texas, and New Mexico, and Cobi, and the burning plains of Asia, are
from 5 deg. to 10 deg. colder than the temperature of the place where the monsoons
are blowing. Would not such a fact be perfectly conclusive in any other
science except theory-swathed meteorology?
2d. The theory assumes that the heated air has an ascensive force, which
causes it to rise and create a vacuum, and this vacuum, by its suction,
draws in the adjoining air, which immediately ascends. The adjoining air,
drawn away from its locality, leaves a vacuum, and that is filled by
another rush from the S. W., and so on, till the Indian Ocean is reached,
and the monsoons are accounted for.
Now, look at the difficulties:
The highest temperature that can be assumed for the air over Cobi, at any
time, without disregarding facts and analogy, is 100 deg.. What is the
ascensive power of an area of atmosphere of 100 deg.? For this we have no
problem or formula, although problems and formulas abound in the science.
Professor Espy relied on heated air only to give the storm a _start_. His
main reliance was on the latent heat supposed to be given out during
condensation, for his ascensive storm power. But over these "burning
plains" there is, according to the theory, no storm or cloud, or
condensation on which that supposed reliance for expansion can be placed.
What, then, is the ascension force of air at 100 deg.? _We ought to know, for
we sometimes have it as high, or within two or three degrees as high, in
all the eastern and middle States._
The monsoons blow at from twenty to twenty-five miles an hour, and
sometimes more. Is that the ascensive force of air at 100 deg.? At 25 miles an
hour it would be 2,200 feet; at 20 miles, 1,760 feet; and at 10 miles, 880
feet per minute.
Does any man believe that either current exists? Why, then, do we not have
our hats taken off, or light objects carried up, or have a monsoon, or, at
least, have the clouds running up, when we have such elevated
temperatures. _Nothing of the kind occurs with us._ Our hottest days are
comparatively still days; and I have seen the cumulus sailing gently to
the east, horizontally, when the air was at 98 deg.. Why should we be exempt?
Is not our air the same and our heat the same?
Again, suppose we grant that the ascensive force is equal to 20 or even 10
miles an hour, will not the adjoining air hold back somewhat to avoid
leaving behind an entire vacuum? or, will it all voluntarily rush in, and
leave a new complete vacuum? and, if so, why the preference of vacuums by
the air, and _when, where, and why_, should the _successive vacuums stop_?
Nay, would not gravity fill the second vacuum from _above_, rather than
from the south-west side? and will not the air incline to rush in, to some
or all these successive vacuums, from some other side than south-west? or,
have these deserts the power of selecting the quarter from which their
vacuum shall be filled, and of delegating it to succeeding vacuums? Would
it not incline to rush in from the east and west where there are no
elevations, rather than from the S. W. and over the Kuenlun Mountains, the
intervening ridges and valleys of Thibet, the lofty Himmalayas, the extent
of India, and the Ghaut Mountains, from three to four thousand feet high,
on its eastern coast? Would it not, at least, _leak in a little_, and
lessen the force with which the vacuums would draw from the far-off Indian
Ocean, so that the monsoon could not blow with equal force? or, if Cobi
and its fellow deserts _must_ and _can_ draw from an _ocean_, why not from
the head of the Arabian Sea, or Bay of Bengal, or the China Sea, which are
nearer, or from the Japan Sea, which is still nearer, or the Yellow Sea,
which is close by? Why draw only from under the central belt of rains?
Nay, what shall be done with Professor Dove? In a recent article,
republished in the American Journal of Science and Art, for January, 1855,
he says: "A greatly diminished atmospheric pressure taking place in summer
over the _whole continent_ of Asia must produce an influx from all
surrounding parts; and thus we have west winds in Europe, north winds in
the Icy Sea, east winds on the east coast of Asia, and south winds in
India. _The monsoon itself becomes, as we see, in this point of view, only
a secondary phenomena._" This looks very like _antagonism_. Who shall we
believe?
Again, suppose you get one atmosphere from the whole area, raised up by
the supposed ascensive force, and at the rate of twenty-five, twenty, or
even ten miles an hour, and a new volume drawn in from the south-west,
and _over the mountains_: will it not take a _little time_ for _that_ to
_heat up_? Does it heat so fast as to _keep up the ascensive force_
without intermission, at twenty-five, or twenty, or ten miles the hour?
What says Mr. Ericsson to this? Can he not arrange with a moderate lens,
to move his engine with the rays of the summer sun? Nay, Lieutenant Maury
says they can not heat up "_per saltum_, or in a day." But according to a
reasonable calculation, they must heat up the air from 80 deg., or less, to
100 deg., at the rate of 2,000 feet per minute. Heating 2,000 feet in depth,
in the proportion of 20 deg. per minute, night and day, for five months, is
"_per saltum_" in a minute, and 1,440 "_saltums_" per day!
And further still, the Indian Ocean, from which the monsoons are drawn to
Cobi and Central Asia to the N. E., is during those months covered by the
belt of calms and rains, as heretofore stated; and the S. E. trades
blowing into it are attributed to the suction created by the ascent of
heated air _there_. So, then, the monsoons are blowing away from under the
rainy belt, from 500 to 1000 miles, to Cobi and the burning plains of
Asia, while the ascensive force of that belt is such as to draw the S. E.
trades toward the very spot, a distance of 1,200 or 1,500 miles, at 20
miles an hour! What must the ascensive force over Cobi, etc., be, if, as a
"stronger power," it can overcome an ascensive force over the Indian Ocean
sufficient to draw the S. E. trades 1,500 miles, at 20 miles an hour; and,
in addition to the force necessary to resist this central suction, not
only stop or hold back the N. E. trade, but reverse it and draw it back,
at 20 miles an hour, as a monsoon? Must it not be, at least, double that
of the belt of calms, or the "great region of expansion," as Professor
Dove calls it?
Now, I am irresistibly tempted to ask whether a meteorological theory can
be too absurd for credence, and whether it would not be as well to endow
the deserts with ribs and lungs, and a proboscis long enough to reach the
Indian Ocean, and the necessary power of inspiration and expiration? Such
a theory would avoid all difficulties, conflict with no more analogies,
and, in my judgment, be as much entitled to credit as the one to which
meteorologists adhere.
3d. North of the Malabar coast, in the north-west of India, lies an
extensive desert. West of that is Beloochistan, with its rainless deserts.
Further west are the rainless deserts of Arabia, and these three,
including the Persian deserts further north, cover _as much surface_ as
the deserts of Cobi and Bucharia--have the sun vertical in part, and
nearly so over the entire surface--_are more intensely hot_, and lie
within _one third of the distance_ which intervenes between that desert
and the Indian Ocean off the Malabar coast, with _an open sea and_ no
_mountains between_. Now, look at it. The north-west desert of India, and
the rainless deserts of Beloochistan and Arabia _reverse no trade_ and
_have no monsoon_, although the Arabian Sea heads right up among them.
They do not attract one from the Indian Ocean off the Malabar coast,
although not more than one third of the distance off, and without such
mountains and table lands intervening as separate that coast from Cobi. It
is said by Lieutenant Maury that the monsoons, "_obey the stronger
force_." But which is the stronger force? Cobi, not _wholly_ rainless,
lying north of 35 deg., under the zone of extra-tropical rains, with India and
the Ghauts, the Himmalaya Mountains, the table lands of Thibet, and the
Kuenlun Mountains between? or the deserts of India, Beloochistan, and
Arabia, _wholly rainless_, and _intensely hot, near by_, and in _open
view_. There can be but one answer to this question. Nothing in the way of
desert barrenness, or elevated temperature, unless it be those of Sahara,
can exceed the deserts about the head of the Arabian Sea and Persian Gulf.
Certainly those of Cobi can not compare with them; yet the trades blow
steadily over them, although more northerly there, as every where, near
their northern limits, especially on land. Says Hopkins, in his
atmospheric changes:
"If any one part of the broad expanse of the continent of Asia could
be heated so as to draw air from the Arabian Sea and the Indian Ocean
during the summer, it would be that part which lies between
Hindoostan and the Lake of Aral, including the region between the
Valley of the Oxus and Persia, and the land of this part, unlike
Hindoostan, is not screened from the sun by thick vapors. But what
says Burnes respecting the winds of this part? Why, that about the
latter end of June, though the thermometer was at 103 deg. in the day,
'In this country a steady wind generally blows from the north.' And
on the 23d of August, after having passed the Oxus--'The heat of the
sand rose to 150 deg., and that of the atmosphere exceeded 100 deg., but the
wind blew steadily, nor do I believe that it would be possible to
traverse this tract in summer if it ceased to blow. The steady manner
in which it comes from one direction is remarkable in this inland
country.' Again--'The air itself was not disturbed but by the usual
north wind that blows steadily in this desert.' And he has many other
similar passages."
Here there is a vast tract of country south of 35 deg. which has a temperature
often of 103 deg., and does not reverse the trade and create a monsoon. How
utterly unphilosophical, then, to attribute the monsoons to Cobi because
they "obey the stronger force!" or to attribute them to it at all.
4th. The monsoons can not be _traced from_ the Malabar coast _to Cobi_.
They do not exist on the south-west of Cobi and near it, where they should
in greatest force, and there is no connection, in fact, shown between
them. They do not often extend more than twenty-five miles inland, or to
the east of the Ghauts. There are no corresponding intervening monsoons
crossing India to the mountains--none over the mountains and table
lands--none under the northern lee of the mountains--nor, in short, on the
whole track, nor any S. W. winds except such as naturally belong to the
action of the curving counter-trade.
Finally, the investigations of Commodore Wilkes on Mauna Loa, a mountain
upon Hawaii, more than 13,000 feet high, and the observations of Professor
Wise and other aeronauts are sufficient to put this whole matter of heated
lands and ascent of the atmosphere as the cause of winds, at rest.
Commodore Wilkes was encamped for about _twenty days_ on Pendulum Peak, in
December and January 1840. Although not up to the elevation of the
counter-trade in that latitude, he was above the local clouds which form
over the island during the day, where the sea breezes blow in with as
great strength as any where. Indeed, he was on the top of the "lofty
conical mountain" to which Caleb Williams alludes in the letter to
Professor Espy I have quoted, and above the spot where Professor Espy
assumed that the clouds were rising with such force as to induce the
strong sea breezes of that island. During this time there were two
snow-storms on Mauna Loa, and they had the wind from the S. W. during the
storm, as might be expected, looking at the situation of the mountain on
the western side of the island. These storms moved to the N. W., and were
observed at the other islands in that direction as rain.
The local clouds lay over the island every day, as they do over active
volcanic islands which are very elevated, although it was the dry season.
_Nothing like an ascent of the clouds or of the currents of air from the
ocean was observed._ On the contrary, the clouds formed before the sea
breezes set in, and the latter blew from the different sides of the island
in under the clouds, and outward again, probably on the opposite side. The
whole interior of the island is elevated, and its temperature low; and
_there was no elevation of temperature on the high portions of the island
over which the clouds formed, and toward which the winds blew, which could
create an upward current_.
"During our stay on the summit, we took much pleasure and interest in
watching the various movements of the clouds; this day in particular,
they attracted our attention; the whole island beneath us was
covered with a dense white mass, in the center of which was the cloud
of the volcano rising like an immense dome. All was motionless until
the hour arrived when the sea-breeze set in from the different sides
of the island; a motion was then seen in the clouds, at the opposite
extremities, both of which seemed apparently moving toward the same
center, in undulations, until they became quite compact, and so
contracted in space as to enable us to see a well defined horizon; at
the same time there was a wind from the mountain, at right angles,
that was affecting the mass, and drawing it asunder in the opposite
direction. The play of these masses was at times in circular orbits,
as they became influenced alternately by the different forces, until
the whole was passing to and from the center in every direction,
assuming every variety of form, shape and motion.
"On other days clouds would approach us from the S. W. when we had a
strong N. E. trade-wind blowing, coming up with cumulus front,
reaching the height of about eight thousand feet, spreading
horizontally, and then dissipating. At times they would be seen lying
over the island in large horizontal sheets as white as the purest
snow, with a sky above of the deepest azure blue that fancy can
depict. I saw nothing in it approaching to blackness at any time."
(Exploring Expedition, vol iv. p. 155).
Here, in the last paragraph, we have the whole truth disclosed. The N. E.
trade was blowing on Mauna Loa, 13,000 feet above the sea, and the
sea-breeze blew in on the _leeward side_, its moisture condensing over the
volcanic island, but without rising _up the mountain_, or _through the
surface-trade_, or _above 8,000 feet_.
So, too, the celebrated aeronaut, Mr. Wise, in the course of more than a
hundred ascensions, some during high wind, and others during rain storms,
never met with an ascending current, except in a single instance, in the
body of a hail-cloud, and then there were descending currents also, the
usual intestine motion of hail-cloud with its opposite polarities.
I copy a description of his passage through the clouds of a rain-storm,
and his floating a long period above them; and there was no ascending
current which disturbed their horizontal repose or progression. The double
layer is not uncommon--condensation taking place at the connection of the
upper and lower portions of the trades, with the surrounding atmosphere;
or in the trade, and by _induction in the surface atmosphere_ at the same
time. Such instances are frequently visible, and if his ascensions had
been undertaken at other times in stormy weather he would have seen more
of them.
"Before I passed the limits of the borough, a parachute, containing
an animal, was dropped, which descended fast and steady, and, just as
it reached the earth, my aerial ship entered a dense black body of
clouds. Ten minutes were consumed in penetrating this dismal ocean of
rainy vapor, occasionally meeting with great chasms, ravines, and
defiles, of different shades of light and darkness. When I emerged
from this ocean of clouds, a new and wonderfully magnificent scene
greeted my eyes. A faint sunshine shed its warmth and luster over the
surface of this vast cloud sea. The balloon rose more rapidly after
it got above it. Viewing it from an elevation above the surface, I
discovered it to present the same shape of the earth beneath,
developing mountains and valleys, corresponding to those on the
earth's surface. The profile of the cloud-surface was more depressed
than that on the earth, and, in the distance of the cloud-valley a
magnificent sight presented itself. Pyramids and castles, rocks and
reefs, icebergs and ships, towers and domes--every thing belonging to
the grand and magnificent could be seen in this distant harbor; the
half-obscured sun shedding his mellow light upon it, gave it a rich
and dazzling luster. They were really "castles in the air," formed of
the clouds. Casting my eyes upward, I was astonished in beholding
another cloud-stratum, far above the lower one; it was what is
commonly termed a "mackerel sky," the sun faintly shining through it.
The balloon seemed to be stationary; the clouds above and below
appeared to be quiescent; the air castles, in the distance, stood to
their places; silence reigned supreme; it was solemnly sublime.
Solitary and alone in a mansion of the skies, my very soul swelled
with emotion; I had no companion to pour out my feelings to. Great
God, what a scene of grandeur! Such were my thoughts; a reverence for
the works of nature, an admiration indescribable. The solemn
grandeur--the very stillness that surrounded me--seemed to make a
sound of praise.
"This was a scene such that I never beheld one before or after
exactly like it. Two perfect layers of clouds, one not a mile above
the earth; the other, about a mile higher; and, between the two, a
clear atmosphere, in the midst of which the balloon stood quietly in
space. It was, indeed, a strange sight--a meteorological fact, which
we cannot possibly see or make ourselves acquainted with, without
soaring above the surface of the earth." (History and Practice of
Aeronautics, p. 209).
This is graphic. Perhaps in relation to the conformity of the upper
surface of the inferior layer of clouds, to the irregularities of the
earth's surface, he was misled during the enthusiasm of the moment. He is
certainly mistaken as to the possibility of observing these double layers
from the earth; I have seen them in hundreds of instances. But in relation
to the _quiescence_ of the clouds for an hour, and _the entire absence of
ascending currents_, he could not be mistaken.
And now, in the absence of all direct proof to sustain the hypothesis,
that the heating of the land produces ascending currents, and thereby the
winds, and especially the monsoons, and in view of all the adverse
evidence, I put it to Lieutenant Maury, and every sincere searcher after
meteorological truth, whether the theory should not be abandoned.