SECTION I.

Of the Causes of the Igneous Meteors, described above.

VARIOUS have been the conjectures of different philosophers about the causes of igneous Meteors: their precise cause has, however, never been ascertained. M. De Luc ascribes them to certain phosphorific exhalations, which ascend from the earth, and take fire or become phosphorescent in the air.* We shall see how this hypothesis will agree with their kind of motion, their peculiarities, and the kind of weather which precedes, accompanies, or follows them.

On the above supposition, must we regard them as taking place in the following manner. The exhalation from the earth must be a circumscribed column of some kind of volatile matter, which, when it arrives at a certain elevation, takes fire: this might easily be

* Nicholson's Journal of Nat. Phil. &c. 1812.

noticed by Arbuthnot, and by the Abbé Bertholon in his “De L'electricité des Meteors. 8vo. Lyons, 1787, vol. ii. p. 25. Where are some curious observations on the Feux St. Elme, Feux Follets, and other Meteors.

supposed to happen to phosphorific matter. There are several other appearances which incline one to think, that there are combustible gaseous exhalations from the earth, which afterwards ignite. The next question is, if they are only phosphorific, as M. De Luc calls them, what is the principle of their ignition? They may, perhaps, be ignited, by getting up into a dryer atmosphere. This supposition is agreeable to the known properties of phosphorus, which is preserved in water, but burns if left to dry. It may perhaps be conceived that phosphorous gases may be preserved while passing through a humid atmosphere; but which, when they arrive at a more dry air, spontaneously take fire. The ignition being thus began, it would probably extend down the column of phosphorific vapour, and give the appearance of a descending luminous ball, just such as we see to be the case: and it might go out when it had descended again so low as to be in an air too humid for combustion. Or its extinction may, in other cases, be caused by the column of vapour being interrupted by wind, or any other cause of dispersion.

Upon the above supposition, the motion of the falling star would be exactly retrograde to

that of the ascending column of phosphorific matter. This is agreeable to the popular notion, that many of these Meteors shoot towards the quarter from which wind will subsequently blow. Because if, as I have shown, the wind often changes first above, its current may give an inclination to the ascending column of phosphorific matter; and the burning star, moving back in an opposite direction, would point to the coming wind. This may often be the case; but I have observed that these stars frequently shoot along in different directions: a circumstance which may be supposed to arise from their previous columns of phosphorific matter being inclined differently by different currents, which, by experiments with air balloons, I have found to exist often in the atmosphere at the same time. If these columns of phosphorific matter ascend from the earth when there are different currents of air in the atmosphere, it may be questioned, how it happens that the motion of the falling Meteor is so straight, and why, on the contrary, it is not bent at angles, as its motion is retrograde to that of an ascending column of gas, which may have passed through, and received an inclination from, several currents of air? Possibly, it

may be replied, between the currents there may be a deposition of water, or some other circumstance, which may extinguish burning phosphorus; and then an alteration of the current may be one circumstance that sets a boundary to its combustion, which in other cases may be continued lower. I can conceive that the change of current might interrupt the continuity of the ascending column; and thus the star might go out when it arrived at the interception of the combustible gas. But it is hard to assign a reason why these columns of gas, if such exist, should not be dispersed entirely by the wind which they must meet with in the progress of their ascent; since they sometimes are seen when the wind is blowing very strongly below. This alone would induce one to believe, that they do not really ascend from the earth; but still they may be formed in the air, perhaps at the junction of two currents. It is moreover difficult to conceive why exhalations from the earth should arise in such narrow columns, as they must do, if this explanation of the phaenomena be true.*

* A Meteor, moving in a very unusual manner, was described at Hackney, on the night of the 7th of November, 1811, about five minutes before nine o'clock, in the North: it moved

If the Meteors in question be caused by the ignition of combustible exhalations, it may be easily supposed that they would vary in appearance, according to the peculiarities of the exhaled gas. Neither is it more difficult to suppose varieties in these exhalations, than to suppose their existence at all. The columns of gas might vary in size at different times, and so give place to Meteors of divers magnitudes. The greater the quantity of the exhaled gas, the less likely would it be to be wholly dispersed by the wind: it might, therefore, be carried along horizontally for miles; and, at length taking fire by dryness of the air, by electricity, or by other causes, might give place to such large, irregular, and horizontally moving Meteors, which appear at uncertain intervals, and travel over vast tracts of country. But this seems to be rather an ingenious hypothesis of M. De Luc, than a theory founded on facts.

There are two circumstances about Meteors,

in a direction to the West: its motion was not regular in a straight line, nor in a uniform curve; but it leaped forward by successive jerks, describing a sort of undulated track ; and it was of considerable magnitude: after being visible for some seconds, it apparently entered a cloud, and disappeared. The circumstance of its peculiar motion is, I think, worthy of record.