which seem to favour an opinion which I once entertained, that they are somehow connected with the combustion of hydrogen. They sometimes end with a loud report. And one kind of them is most frequent after Rain, and in stormy weather. The separation of the gases of water has been mentioned by M. B. P. Van Mons, in a paper given to the Batavian Society. If hydrogen be thus separated, and partly mixed, as it must be, with common air, and should be ignited, we may conceive a Meteor produced: but this is not sufficient to account for their long course which is generally in a slanting downward direction. The occasional report of the Meteor at its termination may be supposed, however, to be caused by its meeting with hydrogen gas in its descent, and setting it on fire. This explosion, too, may interrupt the column of combustible gas, and thus put an end to the Meteor.

In attributing igneous Meteors to the combustion of gases, which ascend from earth, we assume what cannot be proved: for no one has, I believe, seen such columns of combustible gas. There are, however, some circumstances

*

* The opinion of Aristotle about the cause of Meteors seems to agree in some measure with that of M. De Luc. Consult Arist. Meteor. lib. i. cc. 2-4.

which would induce a belief of their existence.* The well known Meteor, called Ignis Fatuus, which appears over marshy grounds, and the Electric Light seen about plants hereafter to be described, which one would naturally attribute to the combustion of terrestrial exhalation, lead us to ascribe more elevated Accensions to a similar cause.

SECTION, II.

Of Aerolites.

THE large masses of substance which occasionally fall from the air vulgarly called Lunar

* On Sunday evening, Aug. 11, 1805, I observed a very unusual exhalation from an elm tree at Clapton, in the Parish of Hackney; the particulars of which are as follow. Between six and seven P. M. the sky being clear, and the weather warm and dry, and wind South East, a column of darkish vapour appeared to arise from the top of an elm tree at some distance: it looked about two or three feet high: after it had continued a few seconds, it disappeared; and, after a few seconds more, reappeared; and continued in this manner, on and off, for nearly half an hour, when it became too dark to distinguish it any longer. More particulars may be found in the Gent. Mag. for 1805, p. 816.

CHAPTER IV.

OF THE INDICATIONS OF THE FUTURE CHANGES OF THE WEATHER.

ONE of the principal purposes to which meteorology may be applied is, that of enabling us to predict, in some measure, the ensuing changes of the weather. In order to do this accurately, a familiar acquaintance with the modifications of the clouds, and indeed with all the operations which are going on above, appears to be necessary. I hardly need lay down the following rule for predicting atmospheric changes. That when two or more contrary inclinations appear, the result must be deduced from those which ultimately prevail; and that when several agreeable signs are seen together, the event may be considered as predicted with additional certainty.* Prognosticks

* A rule laid down of old and sung by Aratus, who says of Prognosticks,

Τῶν μδεν καλοκνησο, καλον δ' επι σηματι σημα
Σκεπίεσθαι, μεμλον δε δυοῖν εις ταυλον ἴοντοιν
Ελπωρή τελεθοι· Πριιτώ δε ες θαρσήσειας.

Arat. Dios. 412.

of weather may be divided into those which result from the observance of the sky, and of meteorological instruments; and those which are deducible from the habits and motions of particular animals and plants.

The popular prognosticks of Rain, Wind, and other changes of the weather, which with little variety are common in most countries, seem to have been known and observed with accuracy of old. Indeed their being familiar to almost every age and country affords the strongest confirmation of their correctness, to those who have not had constant experience of them.

Although we find familiar mention of the Signs of the Weather in the works of Homer, Hesiod, and among almost all the oriental writings, yet Theophrastus the Grecian naturalist, seems to have been the first who cultivated this branch of meteorological science, and collected together the proverbial rules of judging of the weather; which were shortly afterwards put into verse by Aratus the poet, in his Διοσημεια, above two thousand one hundred years ago, and are imitated by Virgil, Lucan, Pliny, Seneca, and others. With little variation, the same rules are to be found

K

Stones, Meteoric Stones, Aerolites, &c. of which accurate analyses have now been published, seem to be made up of ingredients composed in proportions different from those of any known terestrial compound; and are probably formed in our atmosphere; at least such is my opinion, the result of an examination of all the evidence I have been able to collect on the subject. These terrific thunderbolts of Jupiter seem in general to have come down to the earth accompanied by such loud explosions, blazes, and other circumstances as in a less degree attend the larger sort of Fiery Meteors. Indeed all these Meteors may be owing to some common principle of chemical action going on in the higher regions of the atmosphere; which, when more gentle and slow, may only cause the blazing Meteors; but which, when more intense, may go on to consolidate large masses of newly composed substance, and may manifest itself by the fall of Aërolites.* I see no

* An extensive collection of accounts of these phaenomenon was made and published in France. This work was said to be compiled by command of the Emperor Napoléon, who, amidst a life of campaign, imbibed sufficiently the spiritual character of the French nation, to encourage philosophers of all countries, and to attend to the encouragement and promulgation of science.