by which can be determined the amount of heat extricated from air of any given degree of rarefaction, in reducing it to the state of air at the common density. The formula is as follows. Let denote the degree of rarefaction; then 45 (-) will express, in degrees of Fahrenheit, the heat evolved by condensation.

Now at such a height as forty nine miles above the earth, the air is supposed to be more than sixteen thousand times rarer than at the surface; and if the formula were applied to air in this state, the evolution of heat would be immense. But it is not to be supposed that, in the case before us, the air becomes reduced to the density of common air, until the meteor has descended through some distance. Considering, however, the great velocity of the falling body, we may suppose such a density to be attained at an average height of thirty five miles above the earth where the rarity of the air is 1024 times that at the surface. Hence, 45 (1024-1)=46080°. This is the amount of heat which would be extricated by the condensation of air as it exists at the height of 35 miles; but the compression supposed is not that which results from air of this density, but of such as is less dense, commencing with that which is of an extreme degree of rarefaction. The amount of heat therefore would be greater than the estimate here made.

But to form some idea of the intensity of even this degree of heat, we may call to mind, that the temperature required to melt gold is only 5237°; the highest heat of a glass house furnace, 16000°; and the extreme heat required for the fusion of platina, 231770.* The temperature, therefore, elicited by the falling meteors of Nov. 13th, can be compared only to those immeasurable degrees of heat which nothing can withstand, as that of Hare's blow-pipe and deflagrator.

It has been common to resort to electricity as the agent which produces the heat and light exhibited by meteoric bodies; but Biot has satisfactorily shown, that lightning itself is no part of electricity, but is produced by the condensation of air before the electric fluid.

A combustible body falling into the atmosphere under such circumstances, would become speedily ignited, but could not burn freely, until it became enveloped in air of greater density; but on reaching the lower portions of the atmosphere, it would burn with great rapidity.

Henry's Chemistry.

↑ President Clap's Theory of Meteors.

Traité de Physique, Tome II. 459. (Ed. 1816.)

6. Some of the larger meteors must have been bodies of great size. According to the testimony of various individuals, in different parts of the United States, a few fire balls appeared as large as the full moon. Thus Dr. Smith observes (p. 379): "By far the most magnificent meteor crossed the vertical meridian about 3 o'clock A. M. Its course was nearly due west, in length by conjecture about 45°, and at a distance of about 25° south of the zenith. In size, it appeared somewhat larger than the full moon rising. I was startled by the splendid light in which the surrounding scene was exhibited, rendering even small objects quite visible; but I heard no noise, although every sense seemed to be suddenly aroused, if I may so speak, in sympathy with the violent impression on the sight.”*

This description implies not only that the body was apparently very large, but that it was at a considerable distance from the spectator. Now a body in order to appear as large as the moon, will have the respective diameters, calculated for different distances, assigned in the following table.

That is, a body appearing as large as the moon at the distance of 110 miles, must be one mile in diameter; at the distance of 22 miles, one fifth of a mile, or 1056 feet; and even, if only at the distance of a mile, it must be 48 feet in diameter. It may be impossible to decide at which of these distances the meteor seen by Dr. Smith, ought to be taken; but the position with regard to the spectator, the apparent distance, and continued brilliancy indicate, that its real distance was considerable.

Let us, (for a very moderate estimate,) suppose it to have been eleven miles off, and appearing as large as the full moon; it must then have had a diameter of 528 feet. But if any one should choose

* Humboldt says some of the fire balls of 1799 were from 1° to 1o 15' in diameter, and consequently more than twice as large as the moon. (Pers. Narrative III. 332.)

† 240.000: 110 :: 2180:1 nearly.

to limit the distance still farther, say to 1 mile, he must even then admit the actual diameter to have been 48 feet. These considerations, indefinite as they are, are sufficient to show that the body in question must have been one "of great size," agreeably to our proposition.

We may farther infer the great magnitude of some of the meteors from the dimensions of the trains or clouds which resulted from their destruction. These often stretched over many degrees, and at length, were borne along in the direction of the wind, exactly in the manner of a small cloud.

From the remarkable appearances of these objects, it was early supposed that we might be able to identify certain meteors, proving that the same one was seen by different observers, more or less remote from each other, and that we should thus obtain data for estimating the height at which these meteors were extinguished. But the subject is not without its difficulties. On the one hand, there are many circumstances which seem to indicate that the same meteor was seen at different places. Several persons, on reading the notice which I gave of a fire ball that I observed, immediately supposed it identical with one seen by themselves. My account was as follows. "One ball, that shot off in the northwest direction, and exploded a little northward of the star Capella, left, just behind the place of explosion, a phosphorescent train of peculiar beauty. The line was at first nearly straight, but it shortly began to contract in length and to dilate in breadth, and to assume the figure of a serpent drawing itself up, until it appeared like a small luminous cloud of vapor. This cloud was borne eastward (by the wind, as was supposed, which was blowing gently in that direction,) opposite to the direction in which the meteor had proceeded, remaining in sight several minutes." The time was 15 minutes before 6 o'clock.

Mr. Daniel Tomlinson of Brookfield, about twenty five miles W. b N. from New Haven, characterizes a meteor which he saw as follows:

"The time of appearance was about half past five o'clock; it might vary a few minutes from that time. The course was from south to north, varying perhaps from 30 to 50 to the west of north. It started 40 or 5° south of the zenith, and passed directly over head to about the same distance north of the zenith; all who saw it here agree essentially in the foregoing particulars as well as in the followingthat the train, when first seen was nearly straight, rather largest in the middle, and tapering nearly to a point at the south end; that it

instantly contracted in length, and assumed the form of a serpent, with its head to the north; that it continued to contract in length, doubling and crossing itself, and forming a confused line, like that of a loose cord or a piece of tape dropped endwise on the floor, and then gradually dilated, and intermingled its folds, and assumed the form of a light cloud, passing off slowly in an easterly direction." To this description Mr. Tomlinson annexed a drawing representing the successive figures of the train, which agree in general with those observed by myself. The time and other circumstances also accord so well in the two cases, that we can hardly resist the impression that both spectators were observing one and the same object. Proceeding on this supposition, we may form some estimate of the height of this train, that is, of the place where the fire ball exploded. This place being 40° from the zenith of New Haven, and at or near the zenith of Brookfield, distant 25 miles, the elevation above the latter place must have been about 30 miles, that being the tangent of the angle of elevation. It favors the supposition, also, that the large fire balls were extinguished at a considerable height above the earth, that little or no sound was heard, while we should expect a heavy report from bodies of such magnitude, moving with such prodigious velocity through the lower regions of the atmosphere, whatever might have been their density. It appears moreover that whenever a cloud was so situated as to enable the spectator to compare its elevation with that of the falling meteors, the latter appeared the most elevated. Thus Capt. Parker in the Gulf of Mexico saw the fire balls pass behind a cloud, but not one passed between the cloud and the observer; and Professor Hitchcock says that "in no instance was a meteor observed between the clouds and the earth." (See his Essay in the last number of this Journal.) Brydone also testifies, that shooting stars seen from Mount Etna and the highest peaks of the Alps, always appeared as high as when seen from the lowest grounds.

Two difficulties, on the other hand, attending the supposition that the place of explosion was as high in this case as 30 miles, are very formidable. The first is, the great apparent extent of the train, and the second, the velocity of the cloud which resulted from it. The train of this meteor is judged to have been at least 100, and others seen by Mr. Tomlinson were thought to be 40° in length. Since a body balf a degree in diameter at the distance of 30 miles would have an actual diameter of of a mile, it follows that a body 10° in length, must have extended over a space 5 miles long. Again, the cloud mo

ved eastward with a very perceptible progress, equal to that of an ordinary cloud a mile high, carried by a breeze of 10 miles per hour. But in order to move with such an apparent angular velocity at the height of 30 miles, it must have had a real motion of 300 miles per hour. The improbability of either of these suppositions, would lead us to believe, that the place of explosion where the trains were formed, was comparatively near to the earth.

This conclusion is much strengthened by several other considerations. It was the general impression of spectators, that the meteors descended almost to the earth. In this they were doubtless under a mistake, but still the impression is hardly compatible with the supposition, that those bodies were, at the time of their extinction, very high in the atmosphere. Those observers who were on the water, would not be so likely to be deceived in this respect, as those on land; and such, in various instances, testify that they appeared "to come quite down to the water's edge, to reach the tops of the masts," and even "to fall into the water.'

Again, the improbability that the same train, resulting from the destruction of a large meteor, was seen by observers remote from each other, is increased by the fact that trains, which must have been different, greatly resembled one another. Thus the one described by Dr. Hildreth, in a preceding article, (See p. 87,) resembles that mentioned by myself before referred to, almost or quite as much as the one described by Mr. Tomlinson. It was seen at about the same time of day, (twenty minutes before six,) had nearly the same course, exploded near the same place, and left a serpentine train. Yet these three descriptions cannot possibly refer to one and the same body. Indeed the tortuous figure which the trains successively assumed, is very characteristic of the trains of falling stars, and is even recognized in the history of Chinese meteors. (See p. 133.) This peculiar change of figure may be conceived to arise from the action of the wind. The train being left at first in the path of the meteor, is of course straight; but the oblique action of the wind would soon change its form, and may easily be imagined to give it the wavy outline exhibited. Moreover the trains, according to the testimony of various observers, were largest in the center and tapered towards either extremity. This appearance would result from the manner in which the combustion or destruction of the meteor

* See Mr. Schoolcraft's letter p. 139, and the last No. of this Journal, p. 392.