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heat which have already undergone review. Indeed, the supposition appears to my mind not unreasonable, that these latter bodies occasion even a fiercer concussion among the elements than the others, for the reason that they are perhaps larger, and therefore contain within themselves a higher degree of heat.
This I take to be the natural and true source of those wonderful displays of the electric property, that emanate in such surprising quantities from heavily condensed vapor, driven by strong winds, which, beyond all doubt, originate in high and cold regions.
From the united effect of these operations, the influence of which must be inconceivably great, springs that extraordinary change in the disposition and character of the atmosphere which commonly succeeds, and which is at once so grateful and even so necessary to the existence, health, and comfort of the whole animal and vegetable creation. The air, as before remarked, is made elastic, pure, and salubrious, imparting fresh spirits and vigor to every living thing, whether animate or inanimate. The earth is relieved from the great mass of heat that was spread over it, and which, were it of long continuance, would become altogether insupportable. The air by means of it would be rendered unfit for respiration, and life could not be sustained.
In a few instances I have met with these bodies of warm air in the forenoon; but this is not common.
I recollect an instance several years since, in which I had occasion to pass Hudson's river, opposite the city, early in the day. When we were near the Jersey shore, in an open boat, it being about eight o'clock in the morning, with a gentle breeze from the south-west, the day very sultry, we passed through two of these bodies of warm air, which were quite near each other. They seemed to be uncommonly large, and were of such an extraordinary degree of warmth, as to attract the notice of all the passengers. I think they were marked with a higher portion of heat than any I ever recollect to have noticed. About the hour of five or six in the afternoon, a fierce tempest came over the city, and the clouds discharged a large quantity of hail, attended with a more than ordinary emission of the electric property. Many of the hail-stones were as large as ounce balls.
It becomes unnecessary to remark, because the fact is familiar to us all, that after the commencement of cool weather, we have seldom any thunder. The reason of this appears sufficiently obvious. The great portion of oppressive heat is withdrawn from this division of the earth, and its place is supplied with air from the colder regions.
LOOMING. This phenomenon, I presume, is occasioned solely by the agency of the sun operating on vapor. Vapor evidently assumes a very variable character. That which is visible to the eye, and even tangible, goes under the usual denomination of fog. As soon as the power of the sun is brought to act upon it, it immediately becomes rarified, and we see it begin to ascend. After rising to a certain degree of elevation, it forms itself into clouds; but it often hangs
for a time on the declivity of ridges, before it attains that region in the atmosphere which seems to inark the usual distance of the clouds from the earth. While moving in the atmosphere, they reflect the various shades of light, according to their degree of density and their position in relation to the sun.
There is another kind of vapor of a character so extremely subtile, as to be invisible to the eye; though, bad we sufficient acuteness of vision to perceive only a small part of the operation, our wonder, I think, would be greatly excited. This comes under the general denomination of exhalation or evaporation. It comprises all that immense mass, which, by the resistless energy of heat, is absorbed from the boundless surfaces of water, from the earth itself, and from every species of vegetation. At certain periods, the effect of this is so great, that objects at a moderate distance are made to appear indistinct; although, when superficially examined, the atmosphere presents the appearance of much purity and serenity.
From the known properties of light and heat, we can readily perceive, that when they are brought to act on vapor, the effect becomes very striking. Under some circumstances, it is made to reflect various hues; under others, it becomes an extraordinary magnifying power. At times, if we cast our eyes across a body of water, in order to examine a distant shore, we are deceived by an illusion which in some situations is not uncommon, and which seems to be intimately connected with the present inquiry. The water near the shore has the appearance of being elevated, and presents a real obstacle to a correct view of the land. There are three situations at which this phenomenon is sometimes visible when standing on the Battery. One is at the point of Staten Island at the Narrows; another is at the Kills, so called, between the Jersey shore and the north point of the island; and the third is near Weehawk, at the distance of about three miles. There are also other situations on the East and North river, where it is equally visible. The cause can be no other than the influence of light and heat on the current of evaporation, which becomes reflective, while it serves as a magni. fier. It must be borne in mind, that these effects are visible only where high grounds stand in the rear, or are contiguous. The light from these grounds probably has a rëacting tendency, assisting to produce the effect in question; giving to the water the appearance of being raised above its ordinary level, accompanied with a peculiarly luminous aspect. It is my opinion, that when this happens, evaporation may then be supposed to go on with greatest force; for it strikes my mind that this law is by no means uniform in its action. At times its influence would appear to be very great ; at other times partial ; and under some circumstances wholly suspended. All this I conceive to be owing to the state or condition of the atmosphere itself.
But I am strongly inclined to believe, that the manner in which evaporation goes on, differs materially in one respect from what may perhaps be the general opinion. It appears to me that the vapor is drawn together in columns or bodies, and ascends in that way; that it must necessarily be subject to this mode of operation ; and that these columns or bodies in their character and movements are very
similar to water-spouts, but without the capability of producing any visible agitation of the atmosphere, owing to their extreme subtilety. As the ocean presents an extended surface, I think it probable that in some cases these ascending columns are very large ; and when they intervene between a vessel and the land, the effect must be very strong, and consequently the more deceiving. I presume this is that kind of illusion which is familiar to seamen when they approach the land, and wbich, in nautical language, is denominated looming.
It somtimes happens, during the prevalence of a fog in the bay of New-York, that objects present themselves to the eye seemingly very large, but which on a near approach are found to be of inconsiderable magnitude. I never beheld a case, however, in which the illusion made the object to appear so disproportioned and striking as the one mentioned by Mr. Jefferson.* The difference most probably arises from difference of situations.
The real cause of the deception I take to be this : After the sun has attained considerable altitude, and by its influence has dissipated the denser part of the vapor, the rays of light and heat penetrate through the remaining portion, producing a strong magnifying effect; and when, under these circumstances, an object is placed within a certain distance of an observer, (but of the real distance required to produce the effect, I am unable to speak,) it assumes a very imposing aspect, seeming to be much larger than it really is. I think I am correct in asserting, (and to this sentiment I attach great weight,) that none of these phenomena were ever noticed either before the sun had risen or after it had set. Hence I infer, that their true origin and cause must be traced to the influence which light and heat are generally understood to have on vapor; and which, under some circumstances communicate to it a high magnifying, and under others a bright reflecting property.
, In relation to the singular circumstance of a mountain in Virginia assuming various and apparently whimsical shapes at certain periods, it can, in my view of the subject, arise from no other conceivable causes but from those at present under view. As before observed, ordinary evaporation is so extremely subtile as to elude our vision;
*'Having had occasion to mention the particular situation of Monticello for other purposes, I will just take notice that its elevation affords an opportunity of seeing a phenomenon which is rare at land, though frequent at sea. The seamen call it looming. Philosophy is as yet in the rear of seamen, for so far from having accounted for it, she has not given it a name. Its principal effect is to make distant objects appear larger, in opposition to the general law of vision, by which they are diminished. I knew an instance at Yorktown, from whence the water prospect eastwardly is without termination, wherein a canoe with three men at a great distance, was taken for a ship with its three masts. I am little acquainted with the phenomenon as it shows itself al sea; but at Monticello it is familiar. There is a solitary mountain about forty miles off, in the south, whose natural shape, as presented to view there, is a regular cone; but by the eflect of looming, it sometimes subsides almost wholly into the horizon; sometimes it rises more acute and more elevated ; sometimes it is hemispherical ; and sometimes its sides are perpendicular, its top flat, and as broad as its base. In short, it assumes at times the most whimsical shapes, and all these, perhaps, successively in the same morning. Refraction will not account for this metamorphosis ; that only changes the proportions of length and breadih, base and altitude, preserving the general outlines. Thus it may make a circle appear eliptical, raise or depress a cone; but by none of its laws, as yet developed, will it make a circle appear a square, or a cone a sphere.'
Notes on Virginia.
nevertheless, it must at times be of sufficient density to conceal a distant object from view. It is known that the atmosphere in high situations is generally cool; and fog is frequently seen extended in thin horizontal strata on the top of a ridge, becoming visibly condensed on meeting with the cool air above. The effect on invisible vapor we must presume to be the same ; and at times a body of it must be supposed to take the same place, remaining for a while stationary, (subject nevertheless to very sudden and material changes) concealing the top of the ridge from the sight. At the same time, streams of vapor are supposed to ascend from the foot of the ridge, and adhering to its sides in columns or some analogous shape, leave the prominent part exposed to the view of the observer. Sometimes these exhalations ascend in right lines, and coming in contact with the horizontal strata above, it gives to the mountain a quadrangular figure. At other times they are presumed to follow its sides, and meeting on the top in curved lines, it presents a hemispherical figure. And whatever may be the form assumed by the object, whether quadrangular, hemispherical, conical, sunk in the horizon, or whatever else, I feel well assured it is all the effect of the same law. In my opinion it can neither be traced to, nor can it originate from, any other conceivable or assignable cause.
It is remarked of the mountain in question, that it is isolated and solitary, and of a conical form. To this circumstance alone must be owing the exhibition of the strange phenomenon. I venture to assert, that no corresponding appearances were ever observed on a mountain of any considerable continuity, unless aided by distance and some peculiar circumstances, provided its shape and figure possessed the character of uniformity.
Since the foregoing observations on looming were written, I am altogether satisfied of their correctness, and do not now offer them as mere matter of speculation. Any person who wishes to remove from his mind every doubt in this respect, can easily do it. There is one state of the atmosphere alone in which this phenomenon is visible; and this is not unfrequent in the spring and autumn. In summer or winter it is rarely seen.
Whenever a sudden transition takes place from a warm or sultry, to a refrigerative atmosphere, this phenomenon is very visible at the north point of Staten Island ; at the Narrows; and at Weehawk, as before stated. The effect is produced solely by action between the two elements, air and water. The air in such cases being dry, and considerably colder than the water, a powerful evaporation immediately ensues; for the plain reason, that an equilibrium in the operations of nature must be kept up; but, as I have already remarked, it cannot be seen until the light acts strongly upon it. Hence it will be found, that it is scarcely perceptible either before sunrise or after sunset.
It will be evident to every observer who is willing to examine for himself, that in a mere ordinary state of the atmosphere, the ridge in New-Jersey, as seen through the Narrows, presents an almost even line of considerable elevation. In a few instances, I have perceived
the effect of looming to be so strong, that, in the language of Mr. Jefferson, it had almost 'subsided in the horizon. The comb of the ridge only was perceptible, and presented the appearance of small tufts or points.* This, I think, goes to confirm the suggestion before made, that the vapor ascends in columns. The very jagged appearance of those parts of the ridge, seen under such circumstances, I deem conclusive on this point. The steam from boiling water takes that shape, and still farther illustrates the position.
If Mr. Jefferson had taken pains to note the state of the atmosphere, during those periods when the mountain of which he speaks presented those whimsical appearances, I am well persuaded that he would have found them at no time visible, except during the prevalence of such a state of the atmosphere as I have mentioned. Indeed I hesitate not to say, that the principles of philosophy will authorize no other conclusion. And whether on land or on water, the effect is the same, since it must be owing to the same cause. The most skeptical can satisfy themselves in relation to this matter, with very little trouble.
In my next number, I shall present some facts in relation to the transmission of sound through the air, and offer a theory of thundershowers, and of west and north-west winds.
AN OAK BY THE WAY-SIDE.
Thou rear'st aloft thy giant limbs, as if to grasp the skies,
And hark! a shout sounds o'er the hill! - they come, the urchin-rout,
Hadst thou but kept thy forest-haunts, contented with the rest
Alone! - alone, a withered tree, upon the chill way-side!
* I have several times since remarked the fact, that the ridge mentioned above was wholly invisible, and that too in an unusually serene state of the atmosphere, which, however, was highly refrigerative.