The Philosophy of the Weather Part 9

Noon. South. 5 b. c. r. 29.86 76 {Lat. 23 41' N., P.M. 8. South. 6 b. c. r. 29.84 76 {Long. 94 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 36' N., Long. 95 48' W.

Feb. 1. A.M. 4. N. N. W. 7 c. g. 30.29 63 Lat. 22 9' N., Long. 94 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 pa.s.sed 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 pa.s.sed._ 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 pa.s.ses 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 pa.s.sed 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 princ.i.p.al actors, except, perhaps, when it widens out and a.s.sumes 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.

[Ill.u.s.tration: 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 a.s.sert who have stood very near it, and its effects show.

_b_. The track is often as distinctly marked, where it pa.s.sed 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 pa.s.ses 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 pa.s.ses 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 _s.n.a.t.c.hed 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. x.x.xiii. p. 368.)

_i_. In pa.s.sing 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 pa.s.sage 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 pa.s.sage 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. x.x.xvii. 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-gla.s.ses without breaking the gla.s.s. 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. x.x.xvii. 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 circ.u.mstances 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 pa.s.sage 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 s.p.a.ces 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 pa.s.ses 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 a.n.a.logy. 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 pa.s.sage, 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.

a.s.suming, 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 pa.s.sing 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 pa.s.s 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 Inst.i.tute, 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 compa.s.s 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 princ.i.p.als. 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.