“In nearly all great storms which are accompanied with rain, there appear two distinct classes of clouds, one of which, comprising the storm scuds in the active portion of the gale, has already been noticed. Above this is an extended stratum of stratus cloud, which is found moving with the general or local current of the lower atmosphere which overlies the storm. It covers not only the area of rain, but often extends greatly beyond this limit, over a part of the dry portion of the storm, partly in a broken or detached state. Thisstratus cloud is often concealed from view by the nimbus, and scud clouds in the rainy portion of the storm, but by careful observations, may be sufficiently noticed to determine the general uniformity of its specific course, and, approximately, its general elevation.“The more usual course of this extended cloud stratum, in the United States, is from some point in the horizon between S. S. W. and W. S. W. Its course and velocity do not appear influenced in any perceptible degree by the activity or direction of the storm-wind which prevails beneath it. On the posterior or dry side of the gale, it often disappears before the arrival of the newly condensed cumuli and cumulo-stratus which not unfrequently float in the colder winds, on this side of the gale.”“The general height of the great stratus cloud which covers a storm, in those parts of the United States which are near the Atlantic, can not differ greatly from one mile; and perhaps is oftener below than above this elevation. This estimate, which is founded on much observation and comparison, appears to comprise, at the least, the limit or thickness of the proper storm-wind, which constitutes the revolving gale.“It is not supposed, however, that this disk-like stratum of revolving wind is of equal height or thickness throughout its extent, nor that it always reaches near to the main canopy of stratus cloud. It is probably higher in the more central portions of the gale than near its borders, in the low latitudes, than in the higher, and may thin out entirely at the extremes, except in those directions where it coincides with an ordinary current. Moreover, in large portions of its area, there may be, and often is, more than one storm-wind overlying another, and severally pertaining to contiguous storms. In the present case, we see, from the observations of Professor Snell and Mr. Herrick, at Amherst, Massachusetts, and at Hamden, Maine (115 and 135 b.), that the true storm wind, at those places, was super-imposed on another wind; and various facts and observations may be adduced to show that brisk winds, of great horizontal extent, are often limited, vertically to a very thin sheet or stratum.”
“In nearly all great storms which are accompanied with rain, there appear two distinct classes of clouds, one of which, comprising the storm scuds in the active portion of the gale, has already been noticed. Above this is an extended stratum of stratus cloud, which is found moving with the general or local current of the lower atmosphere which overlies the storm. It covers not only the area of rain, but often extends greatly beyond this limit, over a part of the dry portion of the storm, partly in a broken or detached state. Thisstratus cloud is often concealed from view by the nimbus, and scud clouds in the rainy portion of the storm, but by careful observations, may be sufficiently noticed to determine the general uniformity of its specific course, and, approximately, its general elevation.
“The more usual course of this extended cloud stratum, in the United States, is from some point in the horizon between S. S. W. and W. S. W. Its course and velocity do not appear influenced in any perceptible degree by the activity or direction of the storm-wind which prevails beneath it. On the posterior or dry side of the gale, it often disappears before the arrival of the newly condensed cumuli and cumulo-stratus which not unfrequently float in the colder winds, on this side of the gale.”
“The general height of the great stratus cloud which covers a storm, in those parts of the United States which are near the Atlantic, can not differ greatly from one mile; and perhaps is oftener below than above this elevation. This estimate, which is founded on much observation and comparison, appears to comprise, at the least, the limit or thickness of the proper storm-wind, which constitutes the revolving gale.
“It is not supposed, however, that this disk-like stratum of revolving wind is of equal height or thickness throughout its extent, nor that it always reaches near to the main canopy of stratus cloud. It is probably higher in the more central portions of the gale than near its borders, in the low latitudes, than in the higher, and may thin out entirely at the extremes, except in those directions where it coincides with an ordinary current. Moreover, in large portions of its area, there may be, and often is, more than one storm-wind overlying another, and severally pertaining to contiguous storms. In the present case, we see, from the observations of Professor Snell and Mr. Herrick, at Amherst, Massachusetts, and at Hamden, Maine (115 and 135 b.), that the true storm wind, at those places, was super-imposed on another wind; and various facts and observations may be adduced to show that brisk winds, of great horizontal extent, are often limited, vertically to a very thin sheet or stratum.”
Much of the foregoing is graphically described, and unquestionably true. But it may well be asked how he, or others, distinguish which of two or more currents (for there are frequently three, and sometimes four visible), are the true currents of the storm, and which interlopers from another storm? Is thetrue one always the upper one, and why? If the upper one, why is the interloper at the surface noted and quoted to prove what a storm is? How does he know what proportions of the winds he has recorded to show the revolving motion of gales, were the true storm winds of the particular storm? or, that every one of them was not an interloping wind on which the true storm wind was superimposed?
These inquiries are pertinent, for obviously, unless some rule for distinguishing between the currents is given, and there be evidence of direct observation to show that the surface wind, whose direction is noted, is the true wind of the storm, and that thelatteris notsuperimposed, no reliance can be placed upon logs, or newspaper accounts, or registers. There is another element besides direction, viz.: superimposition, a determination of whichisessential totruth. It will be difficult for Mr. Redfield to say that a determination of that element has been made, with certainty, in a single storm he has investigated; and in relation to the convergence of storms, and blending, and superimposition of their winds, I think he is mistaken.
Mr. Redfield is right in saying (American Journal of Science, vol. ii., new series, p. 321) that “too much reliance may be placed upon mere observations of the surface winds in meteorological inquiries,” and yettheyonly have thus far been regarded, and he has proved gyration in no other way. I have frequently, with a vane in sight, asked intelligent men how the wind was, and been amused andinstructed by their inability to state it correctly. Mr. Redfield, in his inquiries, often found two reports of the weather at thesame time, from thesame place, materially different; and I have known, from my own observation, newspapers and meteorological registers to be several points out of the way; and this, because the vanes are influenced by local elevations, and change several points, and very often; because few know the exact points of the compass in their own localities, and because entire accuracy has not been deemed essential. For these reasons, newspaper and telegraphic reports are not always reliable; and therefore, and because, also, storm-winds are easterly and fair winds westerly, and the former veer from east around to west, on one or both sides in many cases, there are few storms which can not be represented as whirlwinds, by a properselectionofreports, a correspondinglocationof thecenter, and anextensionof the lines of supposed gyration, so as to include theprecedingwinds, the actual winds of the storm, and thelateral, andsucceedingfair weather ones.
But, again, Mr. Redfield is right in saying there is, in such cases, “an extended stratum of stratus cloud,” and it is always present. But why does he say thiscovers the storm? Is it distinct from it, and if so, what is it doing there? What power placed it there, and for what purpose? Has this extended stratum of cloud, which forms the canopy of a vast chamber—five hundred to one thousand miles in diameter, and less than two miles in vertical depth, while the earth forms the floor—any agency in producing thewhirl that is supposed to be going on within it, and if so, what? Has the earth any agency, and if so, what? If neither the ceiling nor floor of the chamber have any agency in producing it, what does? Are we to consider thestorm-scudas possessing the power, and as waltzing around the aerial chamber, carrying the air with them in a hurricane-dance of devastation?What, in short, is the power, and how is it exerted?
To these questions, Mr. Redfield’s essays furnish no comprehensive answer. There is an intimation that the cause of storms will be, at some future day, developed. One attempt, and but one, has thus far been made, and that I quote entire:
“We have seen that the two Cuba storms, as well as the Mexican northers, have appeared to come from the contiguous border of the Pacific Ocean.“Now, are there any peculiarities in the winds and aerial currents of those regions, which may serve to induce or support a leftwise rotation in extensive portions of the lower atmosphere, while moving on, or near the earth’s surface? I apprehend there are such peculiarities, which have an extensive, constant, and powerful influence. First, we find on the eastern portion of the Pacific, from upper California to near the Bay of Panama, an almost constant prevalence of north-westerly winds at the earth’s surface. Next, we have an equally constant wind from the southern and south-western quarter, which, having swept the western coast of South America,extends across the equator to the vicinity of Panama, thus meeting, and commonly over-sliding the above-mentioned westerly winds, and tending to a deflection or rotation of the same, from right to left. As this influence may thus become extended to the Caribbean or Honduras Sea, we have, next, the upper or S. E. trade of this sea, which is here frequently a surface-wind, and must tend to aid and quicken the gyrative movement, ascribed to the two previous winds; and lastly we have the N. E. or lower trade, from the tropic, which, coinciding with the northern front of the gyration, serves still further to promote the revolving movement which may thus result from the partial coalescenceof these great winds of Central America, and the contiguous seas.“Thus, while a great storm is, in part, on the Pacific Ocean, its N. E. wind may be felt in great force on that side of the continent, through the great gorges or depressions near the bays of Papagayo or Tehuantepec, as noticed by Humboldt, Captain Basil Hall, and others, the elevations which there separate the two seas being but inconsiderable; and, when the gyration is once perfected, the whole mass will gradually assume the movement of the predominant current, which is generally the higher one, and will move off with it, integrally, as we see in the cases of the vortices, which are successively found in particular portions of a stream, where subject to disturbing influences.”
“We have seen that the two Cuba storms, as well as the Mexican northers, have appeared to come from the contiguous border of the Pacific Ocean.
“Now, are there any peculiarities in the winds and aerial currents of those regions, which may serve to induce or support a leftwise rotation in extensive portions of the lower atmosphere, while moving on, or near the earth’s surface? I apprehend there are such peculiarities, which have an extensive, constant, and powerful influence. First, we find on the eastern portion of the Pacific, from upper California to near the Bay of Panama, an almost constant prevalence of north-westerly winds at the earth’s surface. Next, we have an equally constant wind from the southern and south-western quarter, which, having swept the western coast of South America,extends across the equator to the vicinity of Panama, thus meeting, and commonly over-sliding the above-mentioned westerly winds, and tending to a deflection or rotation of the same, from right to left. As this influence may thus become extended to the Caribbean or Honduras Sea, we have, next, the upper or S. E. trade of this sea, which is here frequently a surface-wind, and must tend to aid and quicken the gyrative movement, ascribed to the two previous winds; and lastly we have the N. E. or lower trade, from the tropic, which, coinciding with the northern front of the gyration, serves still further to promote the revolving movement which may thus result from the partial coalescenceof these great winds of Central America, and the contiguous seas.
“Thus, while a great storm is, in part, on the Pacific Ocean, its N. E. wind may be felt in great force on that side of the continent, through the great gorges or depressions near the bays of Papagayo or Tehuantepec, as noticed by Humboldt, Captain Basil Hall, and others, the elevations which there separate the two seas being but inconsiderable; and, when the gyration is once perfected, the whole mass will gradually assume the movement of the predominant current, which is generally the higher one, and will move off with it, integrally, as we see in the cases of the vortices, which are successively found in particular portions of a stream, where subject to disturbing influences.”
The analogy between this and the theory of Professor Dove, cited above, and prior, in point of time, is obvious. They are substantially alike in principle, with different locations. They differ also in this, Professor Dove appears to think something more than over-sliding necessary, and assigns the duty of crowding the upper current down in to the lower, to make anencounter, to a lateral overflow from Africa. Mr. Redfield seems to think there may be a tendency to deflection when they “over-slide” each other. They are both closet hypotheses, the poetry of meteorology, with something more than poetical license as to facts.
In the first place,no such concurring winds exist in the same locality at the same time. When the inter-tropical belt of rains is over Central America and Southern Mexico, a S. W. monsoon blows in under it, but it usurps the place of all other surface winds; and, when the belt is absent, that portion of the eastern Pacific is most remarkably calm, or is covered by the N. E. trades. Secondly, thetrade-winds every where pursue their appointed course without “tendencyto deflection” by the meeting, or “over-sliding,” or “breaking in,” or “encounter,”of other winds. The great laws of circulation do not admit of any suchconfusion. And, lastly,no storm ever came over the eastern United States from that quarter. The unchangeable laws of atmospheric circulation forbid it. Recent observations also have shown that the storms on the west coast of Central America, and the eastern Pacific, pursue a N. W. course, precisely as in the West Indies, and every where over the surface-trades of the northern hemisphere. IndeedMr. Redfield himself has recently investigated several of them, and admits their course to be north-westerly. (See American Journal of Science, new series, vol. xviii. p. 181.)
But, suppose the co-existence of the winds and the course of the storms admitted as claimed, let us seek for clearer views. What do these gentlemen mean? Do they intend to have us believe the air has inherent moving power, and that the “tendency” of which they speak is an attribute of the winds, and that when they thus meet, and “come into each other,” “encounter,” or “over-slide,” and become acquainted, they wheel into a waltz, and move off northward, “integrally,” with unceasing circular movement, even until they arrive at the Arctic circle? Or is it a mere mechanical effect of meeting, “coming into each other,” or “over-sliding?” If the latter, why a tendency to rotation from right to left? The trade-winds, at least, arecontinuous, unbroken sheets, and not disconnected portions which meet and blow past each other, and there is no warrant for placing themside and side, and attributing to them any such mechanical effect, and as little respecting the other winds. Outside of the fanciful hypothesis, there are no facts to show such a tendency one way rather than the other; and, in accordance with the known facts regarding stratification of the currents of air, no such “tendency” can exist.
But whatpowerimpels the winds, which thus meet at these points? If they be impelled, is it consistent with the action of this power that thewindsit hascreatedandcontrols, should thus assume anopposite “tendency,”and whirl away to the north-eastward, regardless of the power that originated and controls them? What must this “tendency” be, which thusoccasionallynot only diverts the winds from theusually regular coursegiven them by their originating power, but increases their action, from gentle, ordinary winds, to hurricanes? Nay, which gives them a new, resistless gyratory and electric energy, increasing as the new, independent, supposed cyclonic organization moves off, “integrally,” away from “the home of its many fathers,” on a devastating journey towards the north pole?
And, further, if all this were true as to the West Indies and Central America, what is to be said of the billions of other storms, originating on a thousand other portions of the earth’s surface, and how are they to be accounted for, inasmuch as such other “meetings,” “coming into each other,” and “over-sliding,” and “tendency to deflection,” is not assumed to exist?
These questions cannot be satisfactorily answered. The distinguished theorists are mistaken. The stratus-cloud does not over-lie or cover the storm.It is the storm.The winds beneath, whether surface or superimposed, are but its incidents, due to its static induction and attraction. Theirdirectiondepends on the shape of the storm cloud, and its course of progression, and the susceptibility of the surface atmosphere in this direction or that, to its inductive and attractive influence. Theirforceto its depth, its contiguity to the earth, and the intensity of its action; and the scud, are but patches of condensation, occasioned by the same inductive action which affects and attracts the surface current in which they form.
Another objection to Mr. Redfield’s theory of gyration is based upon the fact that in order to constitute hisstorm, to get thegyration, he has to include, at least, an equal amount, generally a great deal more, offair weather. The N. W. wind, the “posterior, or dry side of the gale,” as he calls it (in the foregoing extract), is afair weather wind. It isnecessary, however, to complete the supposedcircle, and it ispressed into the service. The practical answer given to the question, “what are storms?” is, they are cyclones, part storm, so called, andpart fair weather; that is, the stratus-cloud, the scud, the easterly wind, and rain or snow of day before yesterday, were thewet side, or front part of the storm, and the sunshine, clear sky, and N. W. wind of yesterday, to-day, and, perhaps, to-morrow, are the posterior or dry side. When a storm clears off from the N. W. it is notover, it is, perhaps,just begun; and, inasmuch as it storms again, very soon after the wind changes back from the N. W. to the southward, in winter, our weather then is pretty much allstorms.
The statement of this claim seems so absurd that it may appear like injustice to make it. But gyration can not be made out without it, and it is evident in the extract quoted above; in the claim that the winter northers of the Mexican Gulf are parts of passing storms; and clearly and unequivocally advanced as a distinct proposition, as follows:
“1. The body of the gale usually comprises an area of rain or foul weather, together with another, and, perhaps equal, or greater, area of fair or bright weather.” (Am. Jour. of Science, vol. xlii. p. 114.)
Now, in the first place, we must distinguish between a storm and fair weather, before we can tell what the former is, and it is difficult to assent to a theory which explains what a S. E. storm oftwelve hours’continuance is, by includingtwo or three days of succeeding N. W. fair weather wind, as a part of it. There is no proportionate relation as totime, nor any relation as toqualities, or the attending conditions of the atmosphere, nor any conceivableconnection, except the hypothetical one ofgyration, between the two winds.
And, in the second place, it is true, and Mr. Redfield is well aware of the fact, that winds often blow for many days from the N. E., S. W., or N. W., without any preceding or succeeding winds to which they have any discoverable relation. If, therefore, truthwould justify Mr. Redfield in including the fair weather wind, a difficulty would remain which his theory does not cover or explain.
No American, except Mr. Redfield, has been able to discover satisfactory evidence of the gyration of storms, by actual careful observation, or a careful unbiased collation of the observation of others. Professor Coffin is reported to have read to the Scientific Association, at their Buffalo meeting, a paper, confirmatory, in part, but I have not been able to see it. The tracks of tornados have been searched as with candles. When they have been narrow, from forty to eighty rods, their action has been substantially similar, and, although, as we have herein before stated, some irregularities have been found which were consistent with gyration—for irregularities attend the violent action of all forces, and particularly the motion of electricity through the atmosphere, as every one who has seen the zig-zag course of a flash of lightning knows—yet the evidence of two lateral inward currents, or lines of force, has predominated over all others. In all cases, where the path is narrow, those lateral currents are the actors; they constitute the tornado; theirirregularitiesof action produce the exceptions; but the exceptions are neither numerous nor uniform, and do not prove either the theory of Mr. Espy or that of Mr. Redfield. The action is not that of moving air, merely, but of a power exceeding in force that of powder, which nothing but electricity or magnetism can exert. As the path widens, the wind becomes more like thestraight-line gust which follows beneath the ordinary severe thunder-showers. His theory finds no substantial confirmation or support in the path of the tornado.
Several storms were investigated by Professor Espy, some of them the same which Mr. Redfield had attempted to show were of a rotary character; one or two by the Franklin Institute of Philadelphia; one by Professor Loomis, already alluded to; and recently, two by Lieutenant Porter, from logs returned to the National Observatory. None of these investigations confirm the theory of Mr. Redfield. Indeed, Mr. Redfield himself has found it necessary to resort to suppositions ofmodifying causesto explain the evident inconsistencies. It is assumed that the axis, or center, oscillates, and describes a series of circles; and thus, one class of difficulties is avoided. Again, it is assumed that simultaneous storms converge and blend upon the same field, and another class of difficulties are surmounted. And, again, inasmuch as it is notorious that violent gales are rarely if ever felt with equal violence around the area of a circle, but from one or two points only, it is assumed, that the storm winds ascend, superimpose, and descend again, when they return to the place of their first violent action, etc. Thesimple truthrequires no such resort tomodifying hypothesis.
Still, another objection is, that the changes in the barometer, which occur before, during, and after storms, do not sustain the claims of Mr. Redfield or the requirements of his theory.
The barometer sometimes rises before storms. It generally commences falling about the time, or soon after the storm sets in, continues to fall during its progress, and rises again, sooner or later, afterward. This is the general rule.
On this subject Mr. Redfield’s claim is this:
“Effect of the Gale’s Rotation on the Barometer.—The extraordinary fall of the mercury in the barometer, which takes place in gales or tempests, has attracted attention since the earliest use of this instrument by meteorologists. But I am not aware that the principal cause of this depression had ever been pointed out, previously to my first publication in this journal, in April, 1831, when I took the occasion to notice this result as being obviously due to thecentrifugal forceof the revolving motion found in the body of the storm.“Since that period, inquiries have been continued by meteorologists in regard to the periodical and other fluctuations of the barometer, and the relations of these fluctuations to temperature and aqueous vapor. But these incidental causes of variation, in the atmospheric pressure, prove to be of minor influence, and we are left to the sufficient and only satisfactory solution of this marked phenomenon which is found in the centrifugal force of rotation.”
“Effect of the Gale’s Rotation on the Barometer.—The extraordinary fall of the mercury in the barometer, which takes place in gales or tempests, has attracted attention since the earliest use of this instrument by meteorologists. But I am not aware that the principal cause of this depression had ever been pointed out, previously to my first publication in this journal, in April, 1831, when I took the occasion to notice this result as being obviously due to thecentrifugal forceof the revolving motion found in the body of the storm.
“Since that period, inquiries have been continued by meteorologists in regard to the periodical and other fluctuations of the barometer, and the relations of these fluctuations to temperature and aqueous vapor. But these incidental causes of variation, in the atmospheric pressure, prove to be of minor influence, and we are left to the sufficient and only satisfactory solution of this marked phenomenon which is found in the centrifugal force of rotation.”
The average pressure of the atmosphere, at the surface of the ocean, or in the interior of the country, allowing for elevation, is about equal to the weight of a column of quicksilver, thirty inches in height; hence the barometer is said to stand at about thirty inches at the level of the sea.
This is sufficiently accurate for the northern hemisphere, north of the N. E. trades; but the average is somewhat lower in the trades and in the southern hemisphere. Thus, the average of sixteen months, during which the Grinnell expedition was absent, was 30.08⁄100.
From a large number of logs examined by Lieutenant Maury, the mean elevation in the N. E. trades of the Atlantic was 29.97⁄100; the S. E. trades of the Atlantic, 29.93⁄100; off Cape Horn, 29.23⁄100; S. E. trades of the Pacific, 30.05⁄100; N. E. trades of the Pacific, 29.96⁄100. The height of the barometer off Cape Horn is not a fair index of the general elevation of the southern hemisphere, inasmuch as it stands lower there than at the coast of Patagonia and Chili, or at most, if not all, other stations in that hemisphere.
As the barometer is constantly oscillating up and down (irrespective of its diurnal oscillation), it has no known fair weather standard. The point of 30 inches is taken only as it is a mean. I have known it to commence storming when the barometer was at 30.70, and not to fall before it cleared off, below 30.30. And I have known it to be below 30 for several days consecutively, with fair weather. In our climate there is no reliable fair weather standard for the barometer. It falls below 30 without storming; it rises far above, and storms without falling below. No reliance can be placed upon its elevation, except by comparison; but of that hereafter.
The general rule, nevertheless, is, that it falls more or less during storms, whatever its height, and rises sooner or later, more or less, after they clear off.
The difference between its highest and lowest points is called its range. The greatest range observed, and recorded, is about 3 inches—from about 28 to 31—but this range is rare. The range, in the trade-wind region, is comparatively small; in this country itis greater than in Europe; and, generally, the range will be found greatest where the volume of counter-trade, and magnetic intensity, and the corresponding amount of precipitation, and extremes of heat and cold are greatest. One of the greatest ranges during one storm, or two successive portions of a storm, in this country, which I have seen recorded, occurred at Boston, in February, 1842. It was as follows—counting the hours as 24, and from midnight:
These ranges were owing to the alternation of S. E. storms, and N. W. winds.
Taking the first range as a basis, and allowing the height of the atmosphere to be 1,100 feet for the first inch, we have nearly 2,000 feet displaced during one day, if we look for the displacement near the earth, or some 30 or 35 miles, if we soar aloft in the upper regions to look for thelateral overflowof Professor Dove, and about the same quantity restored the next. This brings us to the inquiry, how was it done? It is perfectly idle to talk aboutdifferenceoftemperatureortensionofvapor, theascentof warm air, ordescentof cold in a case like this; or to say that they were occasioned by a lateral overflow of some thirty miles of its upper portion, first this way and then that, in such a brief space of time. The changeis equal to nearly1⁄15of the weight of the whole atmosphere, and the cause, whatever it was, existed within two or three miles of the earth. Mr. Redfield’s explanation I give in his own words, at length:
“One of the most important deductions which may be drawn from the facts and explications which are now submitted, is an explanation of the causes which produce the fall of the barometer on the approach of a storm. This effect we ascribe to the centrifugal tendency or action which pertains to all revolving or rotary movements, and which must operate with great energy and effect upon so extensive a mass of atmosphere as that which constitutes a storm. Let a cylindrical vessel, of any considerable magnitude, be partially filled with water, and let the rotative motion be communicated to the fluid, by passing a rod repeatedly through its mass, in a circular course. In conducting this experiment, we shall find that the surface of the fluid immediately becomes depressed by the centrifugal action, except on its exterior portions, where, owing merely to the resistance which is opposed by the sides of the vessel, it will rise above its natural level, the fluid exhibiting the character of a miniature vortex or whirlpool. Let this experiment be carefully repeated, by passing the propelling rod around the exterior of the fluid mass, in continued contact with the sides of the vessel, thus producing the whole rotative impulse, by an external force, analagous to that which we suppose to influence the gyration of storms and hurricanes, and we shall still find a corresponding result, beautifully modified, however, by the quiescent properties of the fluid; for, instead of the deep and rapid vortex before exhibited, we shall have a concave depression of the surface, of great regularity: and, by the aid of a few suspended particles, may discover the increased degree of rotation, which becomes gradually imparted to the more central portions of the revolving fluid. The last-mentioned result obviates the objection, which, at the first view, might, perhaps, be considered as opposed to our main conclusion, grounded on the supposed equability of rotation, in both the interior and exterior portions of the revolving body, like that which pertains to a wheel, or other solid. It is most obvious, however, that all fluid masses are, in their gyrations, subject to a different law, as is exemplified in the foregoing experiment; and this difference, or departure from the law of solids, is doubtless greater in aëriform fluids than in those of a denser character.“The whole experiment serves to demonstrate that such an active gyration as we have ascribed to storms, and have proved, as wedeem, to appertain to some, at least, of the more violent class; must necessarily expand and spread out,by its centrifugal action, the stratum of atmosphere subject to its influence, and which must, consequently, become flattened or depressed by this lateral movement, particularly toward the vortex or center of the storm; lessening thereby the weight of the incumbent fluid, and producing a consequent fall of the mercury in the barometrical tube. This effect must increase, till the gravity of the circumjacent atmosphere, superadded to that of the storm itself, shall, by its counteracting effect, have produced an equilibrium in the two forces. Should there be no overlaying current in the higher regions, moving in a direction different from that which contains the storm, the rotative effect may, perhaps, be extended into the region of perpetual congelation, till the medium becomes too rare to receive its influence. But whatever may be the limit of this gyration, its effect must be todepressthecold stratumof the upper atmosphere, particularly toward the more central portions of the storm; and, by thus bringing it in contact with the humid stratum of the surface, to produce a permanent and continuous stratum of clouds, together with a copious supply of rain, or a deposition of congelated vapor, according to the state of the temperature prevailing in the lower region.”
“One of the most important deductions which may be drawn from the facts and explications which are now submitted, is an explanation of the causes which produce the fall of the barometer on the approach of a storm. This effect we ascribe to the centrifugal tendency or action which pertains to all revolving or rotary movements, and which must operate with great energy and effect upon so extensive a mass of atmosphere as that which constitutes a storm. Let a cylindrical vessel, of any considerable magnitude, be partially filled with water, and let the rotative motion be communicated to the fluid, by passing a rod repeatedly through its mass, in a circular course. In conducting this experiment, we shall find that the surface of the fluid immediately becomes depressed by the centrifugal action, except on its exterior portions, where, owing merely to the resistance which is opposed by the sides of the vessel, it will rise above its natural level, the fluid exhibiting the character of a miniature vortex or whirlpool. Let this experiment be carefully repeated, by passing the propelling rod around the exterior of the fluid mass, in continued contact with the sides of the vessel, thus producing the whole rotative impulse, by an external force, analagous to that which we suppose to influence the gyration of storms and hurricanes, and we shall still find a corresponding result, beautifully modified, however, by the quiescent properties of the fluid; for, instead of the deep and rapid vortex before exhibited, we shall have a concave depression of the surface, of great regularity: and, by the aid of a few suspended particles, may discover the increased degree of rotation, which becomes gradually imparted to the more central portions of the revolving fluid. The last-mentioned result obviates the objection, which, at the first view, might, perhaps, be considered as opposed to our main conclusion, grounded on the supposed equability of rotation, in both the interior and exterior portions of the revolving body, like that which pertains to a wheel, or other solid. It is most obvious, however, that all fluid masses are, in their gyrations, subject to a different law, as is exemplified in the foregoing experiment; and this difference, or departure from the law of solids, is doubtless greater in aëriform fluids than in those of a denser character.
“The whole experiment serves to demonstrate that such an active gyration as we have ascribed to storms, and have proved, as wedeem, to appertain to some, at least, of the more violent class; must necessarily expand and spread out,by its centrifugal action, the stratum of atmosphere subject to its influence, and which must, consequently, become flattened or depressed by this lateral movement, particularly toward the vortex or center of the storm; lessening thereby the weight of the incumbent fluid, and producing a consequent fall of the mercury in the barometrical tube. This effect must increase, till the gravity of the circumjacent atmosphere, superadded to that of the storm itself, shall, by its counteracting effect, have produced an equilibrium in the two forces. Should there be no overlaying current in the higher regions, moving in a direction different from that which contains the storm, the rotative effect may, perhaps, be extended into the region of perpetual congelation, till the medium becomes too rare to receive its influence. But whatever may be the limit of this gyration, its effect must be todepressthecold stratumof the upper atmosphere, particularly toward the more central portions of the storm; and, by thus bringing it in contact with the humid stratum of the surface, to produce a permanent and continuous stratum of clouds, together with a copious supply of rain, or a deposition of congelated vapor, according to the state of the temperature prevailing in the lower region.”
The italics in the foregoing extract are mine; and, in relation to it, I observe:
1st. There is no cylindrical vessel around storms, andair will not thus resist air. Confessedly, such resistance is necessary. Let any one watch his cigar smoke, and see how readily it moves on, with little momentum. Let any one try the experiment of creating a whirl in theopen air, or in a room, or box of paper, or other material, which can be suddenly removed, with air colored by smoke. I am exceedingly mistaken if he does not find the presence of a “cylindrical vessel,” absolutely essential to prevent the instantaneous tangential escape of the air.
2d. Turn back to page 3 and look at the fall of the barometer in the polar regions (recorded in theextract from Dr. Kane), withscarcely any wind, andas little variationin itsdirection, and see how utterly Mr. Redfield’s theory fails to account for the phenomena.
3d. If I understand Mr. Redfield correctly, he has abandoned the claim as originally made, that the wind moves in circles, expanding, andspreading outby a “lateral movement,” and now asserts that it blows spirally inward, and elevates the air in the center. I quote:
“Vortical Inclination of the Storm Wind.—By this is meant some degree of involution from a true circular course. In the New England storm above referred to, this convergence of the surface-winds appeared equal to an average of about 6° from a circle. In the present case, such indication seems more or less apparent in the arrows on the storm figures of the several charts, where the concentrical circle afford us means for a just comparison of the general course of wind which is approximately shown by the several observations.“Perhaps we may estimate the average of the vorticose convergence, as observed in the entire storm for three successive days, at from 5° to 10°—out of the 90° which would be requisite for a congeries ofcentripetalor center-blowing winds. This rough estimate of the degree of involution is founded only on a bird’s-eye view of the plotted observations. But, however estimated, this involution seems to afford a measure of the air and vapor which finds its way to ahigher elevationby means of the vortical movement in the body of the storm.”
“Vortical Inclination of the Storm Wind.—By this is meant some degree of involution from a true circular course. In the New England storm above referred to, this convergence of the surface-winds appeared equal to an average of about 6° from a circle. In the present case, such indication seems more or less apparent in the arrows on the storm figures of the several charts, where the concentrical circle afford us means for a just comparison of the general course of wind which is approximately shown by the several observations.
“Perhaps we may estimate the average of the vorticose convergence, as observed in the entire storm for three successive days, at from 5° to 10°—out of the 90° which would be requisite for a congeries ofcentripetalor center-blowing winds. This rough estimate of the degree of involution is founded only on a bird’s-eye view of the plotted observations. But, however estimated, this involution seems to afford a measure of the air and vapor which finds its way to ahigher elevationby means of the vortical movement in the body of the storm.”
If the elevation of the air at the borders of the storm, and depression in the middle, resulted from the outward tendency and “lateral movement” of the revolving air, and from thecentrifugal force, as in the experiment with the water in a cylindrical vessel, as stated in the first paragraph quoted, aninvolutionof from 5° to 10° from the action of acentripetal force, must carry the airinward, and thebarometer shouldstand highest in the middle of the storm. The change is fatal to his theory. The two are diametrically opposite in character and effect. In one, the superior strata would be brought down in the center by thelateral pressure outward; in the other, they would be elevated by theinvolution, which “affords a measure of the air and vapor which finds its way to a higher elevation,” etc. It is perfectly obvious Mr. Redfield has refuted his own hypothesis.
In doing this, he is met by the other difficulty alluded to, which he does not attempt to explain. This gathering of the air inward, spirally, by a centripetal force, if it took place, not only would not depress, butmust elevate the barometer in the center, above that of the adjoining atmosphere.
When he first attributed the depression of the barometer to a lateral movement and centrifugal force, he supposed the superior strata descended into the depression, and their frigidity occasioned the condensation, and cloud, and rain. How he now proposes to account for the formation of cloud and rain during storms, while the warm air of the inferior stratum finds its way to a higher elevation in the center of the storm, he does not inform us, and we must wait his time.
“I have,” he says, “long held the proper inquiry to be,what are storms? and not,how are storms produced? as has been well expressed by another. It is only when the former of these inquiries has been solved that we can enter advantageously upon the latter.”
“I have,” he says, “long held the proper inquiry to be,what are storms? and not,how are storms produced? as has been well expressed by another. It is only when the former of these inquiries has been solved that we can enter advantageously upon the latter.”
The former does not seem to be yet solved, or the solution of the latter commenced. Mr. Redfield tellsus (page 259, and onward), that there is an extended stratum of stratus-cloud, which overlies the storm, and that it does not differ greatly from one mile in height. We are not told how the air, which finds its way to a higher elevation during several days continuance of such a storm,gets through the stratum. If he is right itmustdo so, and it would not answer tosupposea very small opening or gentle current through it, to carry off all the air which works inward in a hurricane, during several days continuance. But he does not seem to recognize either the necessity or existence of anyventat all; nor is there any; and this fact is open to the observation of every school-boy in the country; and it is equally open to his observation thatwhen and where the barometer is most depressed, the stratus storm-cloud is nearest the earth. Colonel Reid has much to say about the “storm’s eye,” or “treacherous center” of a storm. A careful analysis of the instances where the “storm’s eye” is noticed will show that the term is applied, in the northern hemisphere, to that lighting up in the W. or N. W., which is the commencement of the clearing-off process, and attended with a shift of wind to the fair-weather quarter:i. e., to W. or N. W. Just such an “eye” as is seen when the last of the storm cloud has passed so far to the east as to admit the rays of the sun under the western or north-western edge of it. The same kind of “storm’s eye” is described in the southern hemisphere, except that the wind shifts to S. W. instead of N. W., that being the clearing-off wind there. No instance of a “storm’seye” in the center of the extended stratum of stratus-cloud, which overlies the storm, can be found recorded, to my knowledge; and it is obvious that Colonel Reid adopts the view of Mr. Redfield, that the westerly and N. W.fair weatherwinds are a part of the storm. So long as these gentlemen hold to that opinion they will never solve the question, “what are storms?” or reach the other, “how are storms produced?”
Notwithstanding, Mr. Redfield asserts, or adopts the assertion, that the inquiry should be, “What are storms?” not “How are storms produced?” that inquiry should be arationalone, and should not violate all analogy, or call for an explanation which science can notrationallyfurnish. Mr. Redfield does not seem to have formed any just conception of theimmeasurable powerof a hurricane,five hundred miles in diameter; or of the nature of thatrodwhich theAlmighty must insert in it, to whirl it with such violent and long-continued force; nor any just conception of the tendency of the whirling mass, in the absence of his “cylindrical vessel,” to fly off, tangentially, into the surrounding air; or of the nature or power of the centripetal force necessary to hold the gyratory mass in its current, and gather it in involute spirals toward a center. Nor has any other man who has witnessed, or read of mountain-tossed waves; of the largest ships blown down and engulfed; of towns submerged, and vessels carried far inland, and left in cultivated fields, by the subsidence of the sea; of sturdy forests and strongly-built edifices prostrated;or listened to the howling of the tempest, and felt his own house rock beneath him, been able to conceive of any known form of calorific or mechanical, or other power, acting from a comparatively small center, which could hold such an immense irresistable mass of whirling air in a circle, andgather itin toward the center in gradually contracting spirals. I confess that, to my mind, it seems little less than a mockery of our intelligence for Mr. Redfield, or Professor Dove, or any other man, how distinguished soever he may be, to tell us that all this is the result of a “tendency to left-wise rotation” of ordinary winds, “coming into each other,” or “over-sliding,” or “meeting,” or “encountering,” on this “front,” or that, down in Central America, or in the West Indies, or the monsoon region; or to talk of “lateral overflows” from mere gravity; of the ascent of warm air, or the descent of cold strata; of theresistance of adjacent passive air, or other mereatmospheric resistancesin connection with suchawful manifestations of power. Their explanations of these phenomena are not rational, nor can they be believed by any rational man, who will bestow upon them half an hour ofcomprehensive, unbiased reflection.
Waiving many minor points of great force, for this notice of Mr. Redfield’s theory is already too much extended for my limits, I am constrained to take issue with him on the fact, and to assert, unhesitatingly, that in amajority of instances no such barometric curve exists.
Doubtless the depression beneath the storm isfound, and exterior lateral elevations may also be had byextending the line into the usual fair weather elevation on each side, as Mr. Redfield is obliged to do, to get his supposed circle of winds at all. Doubtless, too, the seamen sailing out of a storm, on eitherside, and approaching fair weather, will have a rising barometer. But fromfront to rear, on the line of progression, in tropical storms, the curve does not exist on shore, in this latitude, oftener than in two, or possibly three, cases in ten; and then only upon a single state of facts—that is, when there is an interposition of N. W. wind; and this, at some seasons, rarely occurs. An elevation usually occurs before the storm, on its front, if it present an extensive easterly front, as one of these classes does, and adepression is leftafter it has passed off, unless a considerable body of N. W. wind interposes, as heretofore stated. But when there is not such interposition of N. W. wind (for W., W. N. W., or even N. W. by W. will not suffice), there is not an immediate rise of the barometer corresponding in rapidity and extent with the fall, and frequently none during the first twenty-four hours of bright, fair weather. Let the reader, if he has access to a barometer, note this fact, for it is obvious and conclusive.
Finally, there are other atmospheric conditions to which the barometric changes are obviously due:
1st. The counter-trade is of a differentvolume, at different times, over the same locality, and hence a difference in the normal elevations of the barometer.
2d. It is at a differentelevation, at different times,over the same locality. It was so found by the investigations of the Kew Observatory Committee referred to; has been so found by other aeronauts, and may readily be seen by a careful, practiced observer.
It is highest, with a high barometer, in serene weather, when a storm is not at hand; and can sometimes be plainly seen to ascend when a considerable volume of N. W. wind is blowing in beneath, and elevating, simultaneously, the trade and the barometer.
Opportunities occur every year, when the northern edge of the dissolving stratus-cloud is attenuated, and the storm is clearing off in the N. W., with wind from that quarter, and a rising barometer, when its gradual elevation may be observed to correspond with thevolumeof that wind.
3d. During storms, with a low barometer, thetradeand theclouds run low. This, too, is clearly observable, especially when the stratus-cloud passes off abruptly, very soon after the rain ceases. In such cases the barometer will remain depressed for a considerable time, unless another storm supervenes speedily, or the wind sets in from the N. W.
4th. Thetrade, in a stormy state, moves fasterthan when in a normal condition. This is observable during the partial breaks which frequently occur in storms, and at other times. It is also inferable from the more rapid progress of the more intense center, and other intense portions of storms, and the consequent greater depression of the barometer, under such centers or intense portions. (See the storm of Professor Loomis.) It is obvious, also, from the greaterrapidity of progress attending the more intense and violent storms which all investigations discloses.
These simple facts explain all the phenomena:
1st. The trade stratum is a continuous unbroken sheet, and its descent must displace a portion of the surface atmosphere. A portion of it is impelled forward, aiding in the precedent elevation of the barometer, and a portion is attracted backward, into the space from which a like portion had been previously attracted by the passing storm cloud, forming the easterly wind.
2d. The increased progress of the stormy portion of the counter-trade occasions an accumulation in front of the storm, and an elevation of the barometer, and tends also to increase thedepressionunder the spot from which it moves. The latter is, to some extent, counteracted by the thin sheets of surface wind which are drawn in under the stratus from the sides. That which is drawn from the front in successive portions, fills the space from which like portions had been drawn to the westward, and left behind in a passive state by the passing storm. Thus, the surface atmosphere of New England may pass under the entire width of a storm, as a gale; moving now in puffs with great violence, as it passes beneath irregular and intense portions of the cloud, and now moderately; and be left, in a passive state, in Kentucky, occupying the space from which the atmosphere had been previously drawn by the same storm,in like manner, on to northern Texas.
3d. The nearer the stratus-cloud to the earth, thegreater the displacement of surface atmosphere, the lower the barometer, and, ordinarily, the more violent the wind. First, because the same intensity, which, by attraction, brings the trade near the earth, acts with greater force upon the surface atmosphere; and, secondly, the storm winds, which are often most rapid beneath the clouds and above the earth, are likely to be felt with more violence at its surface, where the stratus cloud runs low, especially at sea.
I desire to commend all these facts, in relation to the theory of Mr. Redfield, to the careful attention and observation of those who, although believers in the theory, are not wedded to it; and who have a sincere desire to understand the phenomena which are continually, and thus far,mysteriously, occurring within two or three miles of us, while our knowledge of the distant worlds around us—the science of astronomy—seems almost perfect.
I will return to a further and a careful consideration of the nature of the reciprocal action between the earth and the counter-trade, and the facts bearing upon the question, in another chapter. It is obvious that received theories can not aid us materially in the inquiry.
We are yet ignorant of the true nature of magnetism. We trace its lines, as in the diagrams, upon and around the magnet; but we can only do this with soft iron, or other substance, in which magnetic action may be induced. We know that these lines are currents, or lines of force, for that force produces sensible effects, and we measure it by the movements of the needle. We know that these lines may bedeflectedby other magnetic bodies, and concentrated upon them. We know that the earth, and the smallest magnets, exhibit properties in common. The poles of the magnet are some distance from its extreme ends—so are those of the earth. The intensity increases, from the center, or near it, to the poles of the magnet, as shown by its attraction; and the same increase of magnetic intensity, from the magnetic equator to the magnetic poles, or near them, is traced upon the earth.
We know that there are two lines, or ratherareas, of greater intensity upon the globe. One extending from the American magnetic pole, south-eastwardly, to a corresponding pole in the southern hemisphere; and another, the Asiatic, extending from the Siberian pole to a corresponding southern one, in like manner.We know that, from those lines or areas, the intensity, east and west, on the same parallel of latitude, decreases each way, to about midway between them. Thus, calling the intensity where Humboldt found the magnetic equator over South America, in 7° 1′ south latitude, 1, or unity—the least intensity known is, .706, found at the magnetic equator, over the South Atlantic, and at its most southern depression; and it increases to 1.4 in the West Indies, and to 2.0099 upon one or more points of the North American continent, south of the magnetic pole, and about the meridian of 92°. That it is 1.805, at Warren, Ohio, in latitude 41° 16′, and longitude 72° 57′, and decreases to 1.774 at New Haven, Connecticut, in latitude 41° 18′. That it is but 1.348 at Paris, nearly one third less than on the same latitude in some portions of this continent. That the line of equal intensity, or “iso-dynamic” line, of 18⁄10, is a closed curve of an oval shape, extending somewhat below 40°, in the longitude of Cincinnati, and reaches off nearly to Bhering’s Straits, on the west; rising in a similar manner, though not so abruptly, on the east; including the great northern lakes and a considerable part of Hudson’s Bay. While the iso-dynamic lines of 185⁄100, and 1875⁄1000, are smaller ovals, included within the former. Such, at least, is the present belief from such investigations as have been made. (See an article by Professor Loomis, American Journal of Science, new series, vol. iv. p. 192.)
Our subject demands a still closer examination ofthe elements of magnetism and its associated electricities, and their influence upon climate and the atmosphere with a view to the solution of the questions in hand, and we will pursue the inquiry in the present chapter.
Waiving, for the present, any further notice of the fact that the counter-trades are concentrated over, and contiguous to, this area of intensity, for the purpose of examining the magnetic phenomena independently, and intending to return to a consideration of their connection with it, we observe:—That it is now well settled that the iso-geothermal lines, or lines of equal terrestrial heat, are coincident, or nearly so, with the lines of equal magnetic intensity. The points where the magnetic intensity is at a minimum, on the magnetic meridian, are the warmest points of that meridian, and those where it is most intense, the coldest.
The magnetic elements of a place may be computed from its thermal ones. The laws producing or governing the distribution of one, have an intimate physical relation with those producing or governing the other. Professor Norton ably sums up a discussion of the subject (in the American Journal of Science for September, 1847), omitting the theoretic propositions, as follows: