Obrazy na stronie
PDF
ePub

OBSERVATIONS

ON ELECTRICITY, LOOMING, AND SOUNDS : TOGETHER WITH A THEORY OF THUNDER

SHOWERS, AND OF WEST AND NORTH-WEST WINDE.

[blocks in formation]

There are certain periods in the state of the atmosphere, when it seems altogether reasonable to suppose that evaporation goes on with increased force; and I think we are warranted in the conclusion, that the mass of ascending vapor presents a material obstacle to the transmission of sound. I have frequently observed, during the prevalence of sereve and pleasant weather, that the conveyance of sound to any considerable distance was attended with a great deal of difficulty. At other times, without much apparent change, sound would appear to move with the utmost ease, meeting with no impediment, and spreading over an extended surface. The nature and cause of this, in my opivion, admit of a satisfactory explanation.

Whether sound appears to move with ease, and to strike the ear in a clear and distinct manner, or whether it meets with a resisting agent, and falls upon the ear in a way that seems to be imperfect and murmuring, I conceive it to be wholly owing to the principle or law of evaporation. When the agency of this power is exerted in its full strength, it follows as a natural consequence, that the atmosphere must be highly charged with this subtile fluid. And although it is ordinarily as imperceptible as the air itself, it must, from the nature of the case, occupy a large portion of space, and possess in a high degree the properties of the element from which it is chiefly drawn. Under such circumstances, it is easy to perceive, that sound cannot proceed as far, nor indeed, one would think, with the same velocity, as when there is a feebler resisting medium. And that there is often a surprising difference in the condition of the atmosphere in this respect, can hardly have escaped the observation of any man.

It is within the knowledge of most people, that owing to some cause not generally understood, the state of the atmosphere at times is such, in which an extraordinary degree of stillness seems to reign, that sounds which are not unusually loud, are heard at a great distance. The sound of men's voices in conversation has been sometimes heard across the water, for the distance of near two miles. The crowing of a cock may then be heard so far that, were it not a fact of common notoriety, it would be deemed incredible. I recollect an extraordinary instance, though of a different kind, that comes strongly in point. At one of those still periods, I heard very distinctly at the Battery, the sound of a conch-shell, that was evidently blown at the ferry on Staten Island, a distance of seven miles. My opinion at the time was, it could have been heard at least two miles farther up Hudson's river. The sound was most probably somewhat aided by a gentle movement of the air from that quarter. These and similar occurrences are common in the bay of New-York; and

14

VOL. XI.

must necessarily be so in every place where there are large bodies of water. It is a remark frequently made among people in the country, when this kind of stillness recurs, and sounds from different quarters are heard distinctly, that it forebodes a change of weather. As a general remark, it may be said to be strictly warranted by experience. It is my belief that there are but few instances in which ihese indications are not quickly followed by discharges from the clouds.

I ascribe these phenomena to one cause only. It seems clear to my understanding, that during the prevalence of this state of things, there is a total suspension of the power of evaporation; and that such periods must constantly and necessarily succeed a loaded atmosphere, will be readily believed. The facts already mentioned I deem satisfactory on this point. There can remain consequently but very little resistance to the movement of sound; the whole of the vapor having ascended to the higher regions, leaving the lower portion of the atmosphere completely disburdened. And the circumstance that it soon returns to the earth in showers, is strongly corroborative of the position.

That the operation of the principle of evaporation should be suspended when the higher regions of the atmosphere are completely Ioaded with vapor, must be supposed to be a consequence following so naturally as scarcely to admit of doubt. For it would not be consonant with common sense to imagine, that while copious streams were in readiness to descend from the clouds, the law of evaporation should remain in force.

[ocr errors]
[ocr errors][merged small]

That the element of heat governs and controls all the others, and is the prime cause of every movement, and of every change or modi. fication to which they are subject, there can exist no doubt. Its power seems proportioned to the magnitude and splendor of the object that dispenses it; and all nature attests its supreme potency. So copiously indeed does the great fountain pour it upon our planet, and such is its transcendant influence, that some powerful rëacting agent was required in the system, in order to keep up the charm of freshness and beauty on the face of creation, and io preserve health and life in the nameless grades of existing beings.

There are numerous reasons for supposing, that during the prevalence of summer heat, there must be a great inequality in its distribution over the surface of the ground. The positions and altitudes of numberless ridges and mountains, and of ihe knobs, spurs, and diverging lines of those ridges and mountains; of the many inter vening plains and valleys; of great lakes, bays, and rivers, and of the falls and rapid currents of many of those rivers ; together with the constant but variable influence of the mighty ocean, with the ceaseless flux and reflux of its once inexplicable tides, all unite to produce this effect. The setting of currents of air from cold or warm regions, which fluctuate incessantly, contributes essentially to the same end. Hence we find, that it is no uncommon thing for one portion of our

continent to be for some time severely oppressed with a sultry at. mosphere, invariably experiencing a corresponding degree of vivid lightning and loud thunder, while a different division shall remain comparatively cool, and much exempt from those phenomena.* But it must not be forgotten, that in proportion as the heat is diminished, in that proportion do we always find the absence of thunder and lightning. This fact is indeed familiar to every person capable of observation.

Arguments are not necessary to show the constant efforts of nature to keep up a general equilibrium in her movements. This is visible every where ; and so long as the vital principle of heat shall continue to be profusely spread upon the earth, and so long as its resistless energy is 'felt through nature's depths,' so long will the whole phenomena of thunder-showers, hail storms, hurricanes, and furious winds, with all their inseparable concomitants, be the undeviating and natural consequence. The vivifying effects which immediately spring out of these convulsive movements of the elements, sufficiently point out the cause, while they demonstrate their efficacy and usefulness.

A high degree of heat is seldom known to prevail for several successive days in any section of country, without being succeeded by a fierce tempest.

One cannot exist, without the certainty of producing the ciher. This operation will be as constant and as durable as the existence of those laws to which, under the present system of things, the whole are subject; for cause and effect must remain unchangeable.

Here, however, it may be proper to remark, that notwithstanding the intense heat of the summer of 1825, which exceeded in degree and duration any thing that we have an account of, perhaps no season ever passed off in which, not only at this place, but for an extended district contiguous to it, there were fewer thunder-showers, or so small a display of the electric property. But it will be remembered, that in other parts of this state, and in various parts of the United States, tempests of a most terrific nature were experienced. From the numerous accounts detailed in the gazettes, we are authorized to believe, that so much destruction was never before produced in one season from the same cause. Whole districts of country were swept by tremendous winds; vegetation of every kind prostrated and cut to pieces by the most extraordinary quantities of hail, some of which was of enormous size; and many people and animals were killed by the lightning.

To show the rapid operation of the elements upon each other, I would simply refer to a metal or glass vessel filled with cold water in a sultry day. It will be perceived, that in a few minutes the whole surface of the vessel will be covered with water; and the ordinary term which people make use of to express their idea of it, is sweating.

* It will doubtless be recollected by many, that during a part of the summer of 1824, the heat in the southern portion of the United States was ielt to a degree never before known, which was attended by very terrific thunder and lighining. During the prevalence of these phenomena in ihat direction, it cannol be forgotten that in some of the northern and middle states, the season was unusually cool, and marked with inconsiderable electrical displays.

But it is well known to be occasioned solely by the powerful influence which a mass of cold water, and metal or glass of equal coldness, have on a very sultry and humid atmosphere; the warm air rushing strongly into the colder and denser element, which it continues to do until the water in the vessel becomes of the same temperature as the circumambient air itself. By this operation, the moisture soon accumulates to such a degree as to form large drops, which fall from the sides of the vessel.

The same effect, though the operation be reversed, may often be seen in winter, when the cold is severe. The windows of a room without shutters, in which a fire has been kept up through the day, will be found the next morning to be completely coated with ice. This is produced by a cold atmosphere acting on a warm one, after the fire is extinguished, but the warmth retained. The external moisture which lodges on the glass, but which cannot enter the room, soon becomes completely congealed.

Of the immense quantities of vapor that are exhaled into the atmosphere, and which are sometimes so abundant as to skirt the whole heavens, always floating in or near the cold regions, large portions must necessarily be drawn to those sections of the country that are overcharged with heat; and hence the very common occurrence of thunder-showers in the afternoon. Such frequently is its overbearing ascendancy during the day, that some time before sun-down we perceive clouds rising in the north-west, which, by means of the wind being drawn from that direction, (it being the quarter from whence proceed the coldest currents of air,) soon multiply and spread, until they gather sufficient strength to produce in their course all their usual and interesting characteristics. The infinite inequalities in the surface of the ground, connected with the causes before mentioned, must give rise to the constant succession of these operations, in numberless portions of the country, and to the great diversity in their character. Some showers afford bountiful supplies of water, and copious emissions of the electric property; while others are limited in their effects in both of these particulars.

The heat in any district must be supposed to multiply, until its influence shall become so predominant as to be felt in those cold regions that are nearest to it. Action and rëaction quickly succeed – a consequence which I presume must immediately follow — and the effects must always be proportioned to the force and peculiarities of the combined causes. Currents of cold air will often set strongly in that direction ; sometimes rushing with extreme impetuosity. This cannot take place, without carrying along with them large bodies of vapor, which are speedily condensed to such a degree as to form heavy, dark, and extended clouds; and this condensation must beget showers of rain in proportion to their depth, surface, and compact

If they rise to an unusual height in the atmosphere, it appears to me the cold is communicated through them in the like degree to the earth; for that they serve as a medium through which heat and cold are equalized, is a conclusion that I believe will not be disputed. The inference therefore seems reasonable, that vapor must be very much condensed, and extend to a great height, before it reaches those extreme cold regions which are sufficient to congeal the water, and occasion it to fall in masses of ice.

ness.

Mr. Volney, in his view of the United States, suggests the probability of occasional vertical currents; but if my memory serves me, he barely makes the suggestion, without proceeding to trace their general influence or agency. Had he pursued the theory, he would beyond all doubt have established it not only to his own, but to the satisfaction of every reader. It has often struck me as matter of surprise, that so little has been said on this subject; and the more so, as it appears to me a position as important as it is undeniable. That almost all the great changes which are so frequently felt in our atmosphere, are brought about through this medium, I believe to be capable of sufficient demonstration. The usual serenity of the air consequent on these changes, is itself a pretty clear evidence of it. Strong horizontal currents, of great extent, could only bring with them the impure exhalations of boundless forests, extensive morasses, and great inland seas. These could neither produce a serene atmosphere, nor could they yield that portion of health and comfort which are required by nature in her complicated and infinitely varied concerns. Such movements would not only be contrary to every principle of that wise and rational economy, which is one of the most prominent features in all her multifarious works, but they would be attended with such wide-spread ruin, as in a great measure to counteract all those kind and beneficent intentions which, under all circumstances, and in all seasons, are so striking and manifest, even to a superficial observer.

I have the fullest faith in a constant succession of these operations ; and am persuaded, that to this cause more than to any other, nay, infinitely more than to all others, is to be ascribed the coolness, freshness, and serenity, so commonly experienced after a thunder-storm. It is difficult to conceive from what other quarter such delightful changes should come, or how and by what other means effects so extraordinary should so soon be brought about. The common fact that these currents, in the great majority of cases, come from the north-west, furnishes no argument that they proceed from remote cold regions in that quarter; because nothing is more common than the occurrence of a thunder-storm, not only in the maritime districts, but frequently very far in the interior, attended with furious winds that sweep over the face of the country, producing much devastation, while another district, not very far to the north or north-west of it, shall experience a calm and serene atmosphere. If any man will be at the trouble to make suitable inquiries, he will find this to be an almost every day occurrence in the summer season. And the operation of these causes thus explained, presents itself to my mind as not less correct and simple in theory, than it is obviously beneficial and delightful in its results. Hence I conclude, that there can be little doubt or hesitation entertained that it is one of the permanent laws in our system, and that to the operation of this law are we constantly indebted for nameless enjoyments and benefits. The circumstance that currents of air at such times set strongly from the north-west, is an objection of very little weight against the prevalence of vertical currents; for as the maritime districts are univer.

« PoprzedniaDalej »