weather, the passage of the meridian. It has been remarked that, during rainy days, bad weather is always a little interrupted about the time when the moon passes the meridian. We must, however, make an exception to this rule as often as the angle of the moon does not coincide with that of the sun. As these observations may be very easily made, by means of astronomical tables, in which the angles of the moon and sun are marked, they are exceedingly well calculated to prove the truth of this system. No one, for instance, will refuse assent to it, when the daily changes correspond with the angles of the moon; and when independently of the effects of the moon's situation, the horizontal effect of the moon at rising and setting is different from that produced by its passage over the meridian.

It rains oftener in the day time than in the night, and oftener in the evening than in the morning.

Linnæus advised his countrymen to observe with care the opening of the buds, and the unfolding of the leaves of trees, as a method of judging the forth-coming weather. The ignorant farmer, says he, tenacious of the ways and customs of his ancestors, fixes his sowing-season generally to a month, and sometimes to a particular day, without considering whether the earth be duly prepared to receive the seed; hence it frequently happens, that the fields do not yield a produce correspondent to his sanguine expectations. The wise economist should therefore fix certain signs by which to judge of the proper time for sowing, We look up to the stars, and, without reason, suppose that the changes on earth will answer to the heavenly bodies: entirely neglecting the things which grow around us. We see trees open their buds, and their leaves expand, whence we conclude that the spring is approaching, and experience supports us in the conclusion; but no one has yet been able to shew what trees Providence intended should be our kalendar, so that we might ascertain on what day the countryman ought to sow his grain. Although it cannot be denied but that the same power, which brings forth the leaves of trees, will also cause the grain to vegetate: nor can any one justly assert that a premature sowing will uniformly accelerate a ripe harvest. No means therefore seem to promise success so much, as the taking of our rule for sowing from the leafing of trees. With this view it must be observed in what order every tree puts forth its leaves, according to its species, the heat of the atmosphere, and the quality of the soil. Afterwards by comparing together the observations of several years, it will not be difficult to determine, from the foliation of trees, (if not certainly, at least probably,) the time when annual plants ought to be sown. It will be necessary likewise to remark what sowings made in different parts of the spring produce the best crops, in order that by comparing these with the leafing of trees, it may appear which is the most proper time for sowing; nor will it be amiss in like manner to note at what times certain plants, especially the most remarkable in every proyince or country, blow; in order that it may be known whether the year makes a quicker or slower progress.

Pliny has similar observations, Why, says he, does the husbandman look up to the stars, of which he is ignorant, whilst every hedge and tree point out the season by the fall of their leaves? This circumstance will indicate the temperature of the air in every climate, and shew whether the season be early or late. This constitutes an universal rule for the whole world; because trees shed their leaves in every country This according to the difference of the seasons. gives a general signal for sowing; nature declaring that she has then covered the earth against the inclemency of the winter, and enriched it Nat. Hist. 1. xviii. c. 25. with this manure.

Virgil counsels us on this subject.
Mark well the flowering almonds in the wood;
If od❜rous blooms the bearing branches load,
The glebe will answer to the sylvan reign,
Great heats will follow, and large crops
of grain.
But if a wood of leaves o'ershade the tree,
Such and so barren will thy harvest be.
In vain the hind shall vex the threshing-floor,
For empty chaff and straw will be thy store.

Dryden. Georgic, i. 1. 272. Mr. Kirwan, an ingenious contributor to the Transactions of the Royal Irish Academy, (vol. v. p. 20, &c.) has endeavoured to discover rules for prognosticating the different seasons in Great Britain and Ireland, from tables of observations alone. On comparing a number of observations taken in England from 1677 to 1789, (a period of 112 years) he found:

1. That when there has been no storm before or after the vernal equinox, the ensuing summer is generally dry, at least five times in six

2. That when a storm happens from an easterly point, either on the 19th, 20th, or 21st of May, the succeeding summer is generally dry at least four times in five.

9. That when a storm arises on the 25th, 26th, or 27th of March (and not before) in any point, the succeeding summer is generally dry, four times in five.

4. If there be a storm at south-west, or westsouth-west, on the 19th, 20th, 21st, or 22d of March, the succeeding summer is generally wet, five times in six.

In this country winters and springs, if dry, are most commonly cold; if moist, warm:-On the contrary, dry summers and autumns are usually hot, and moist summers cold; so that, if we know the moistness or dryness of a season, we can form a tolerably accurate judgment of its temperature. In this country Mr. Kirwan remarks, that it generally rains less in March than in November, in the proportion at a medium of seven to twelve. It generally rains less in April than October, in the proportion of one to two, nearly at a medium. It generally rains less in May than September; the chances that it does so, are, at least, four to three; but, when it rains plentifully in May (as 1.8 inches or more,) it generally rains but little in September; and when it rains one inch, or less in May, it rains plentifully in September.

From a table kept by Dr. Rutty, in Dublin, for forty-one years, this author endeavours to calculate the probabilities of particular seasons being followed by others: and although his rules chiefly relate to Ireland, as there exists but little

After all, some of our readers may think this subject hardly worth pursuing to such an extent;

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a list of practical observations on facts, occasionally interesting to all men. See BAROMETer, CLOUDS, METEOROLOGY, and WEATHER. ÆROMELI, in natural history, a name given

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EROMETRY, comprehends not only the doctrine of the air itself, considered as a fluid body; but also its pressure, elasticity, rarefaction, and condensation. But the term is at present not

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AIR BALLOON.

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1. ÆRONAUTICS, or ÆRONAUTICA, of anp, ναυτική, from vavę, a ship, the art of sailing in, or navigating the air. This term has superseded that of ærostation in scientific treatises, as more correctly expressing the art of guiding ærostatic machines; ærostation more perfectly denoting the weighing of air, or of bodies sus pended therein. Our plan, in treating of this art is,

I. To furnish a sketch of its PROGRESSIVE HISTORY, Or the various early attempts of Eronauts.

II. Of attempts to improve the STRUCTURE of ERONAUTIC MACHINES.

III. Of the PRINCIPLES of their CONSTRUC

TION.

IV. Of the actual MAKING, and FILLING BALLOONS.

The principle of all æronautic machines was no doubt, first suggested by fact. Certain bodies were seen to ascend.-Fact led to experiment. Erostatic machines ascend not because they are freed from the influence of gravitation, and there fore have no weight, but because the gas with which they are filled, is specifically lighter than the surrounding air. It is a doctrine of Hydrostatics, that if a body be lighter than a fluid, in equal proportions, that fluid will bear it up, and it will float upon the surface, as the cork swims upon the water; and, hence a body lighter than our atmosphere, will float upon the atmosphere

and ascend. If the higher and lower regions of the air were every where equally dense, a lighter body would ascend directly to the surface, and there remain perfectly quiescent, and would have no more tendency to descend into the inferior regions, than a blown bladder has to sink into the water; which it cannot do, unless oppressed by the weight of some more solid adjunct: which together with itself, exceeds the gravity of the water. But the air is subject to two great principles. Compression and expansion, existing however in different proportions, at different degrees of temperature and elevation above the earth. The vast body of air that lies in the superior regions, continually pressing its immense weight upon that below, thereby renders it exceedingly dense, so that it becomes impossible for it to rarefy itself to any considerable extent, and therefore as we ascend the upper stratum of the firmament, the atmosphere becomes less dense by reason of the diminished pressure of the superincumbent air, and in the extreme regions is perfectly elastic and subtle; a light body therefore, instead of rising to the top, will only rise to a height where the air is of the same specific gravity with itself, and in that altitude will remain quiescent, in proportion as the air is more or less agitated: or, it will be carried before the winds and receive different motions, according as it is acted upon by surrounding currents of atmosphere. It is exactly so with the balloon, which

being extended to a considerable bulk, and filled with air, considerably lighter than the common air, naturally ascends.

2. This invention, therefore, has in the course of the last century, become the popular substitute for the old attempts of mankind to construct wings, &c. for flight. It is somewhat curious to observe the pertinacity with which men, in all ages, have prosecuted some kind of bold attempt to rule in air. To say nothing of Icarus, and his fabled wings, or of the automata that have been made ingeniously self-moving, the pretensions of magicians, and the long supposed achievements of witchcraft in this field, angels and dæmons have been alike clothed by human credulity with the attribute of flying; and while philosophy has exploded many of the pretensions of the latter, our pictorial illustrations of scripture, and even the finest paintings perpetuate the claims of angels to wings, with almost unquestioned uniformity.

3. Two of the latest attempts of mankind in this way, may be amusing to the reader. During the reign of James IV. of Scotland, a pseudo philosopher of Italy, presented himself at the court of that monarch with loud pretensions to science, and having been made abbot of Furyland, to allow him learned leisure, offered in presence of the court, to start from the walls of Stirling Castle upon wings, of his own construction, and pass through the air to France. This adventurer must have possessed some kind of sincere confidence of his success, for he actually manufactured an immense pair of wings, which he crowded with plumage of all sorts, and launched from the walls of the castle on the day appointed. Soon, however, he descended to parent earth, and broke his thigh in the fall. His apology to the disappointed spectators was full as bold as his attempt; but it seems to have been received. My wings,' said he, being composed partly of the feathers of dunghill fowls, they, by a certain sympathy, were attracted to the dunghill had they been composed of eagle's feathers alone, the same principle of sympathy would have attracted and kept them upwards!'

4. The second attempt of this kind we shall notice, was made at Tubingen, in Wirtemberg, in 1628. Here a learned rector of the public school, named Keyder, had been for some years insisting upon the possibility of attaining the art of flying, but sagaciously confined himself to warmly lecturing on the theory. But a monk of the neighbourhood became a sincere disciple, constructed wings of the approved description, and from a high tower in the neighbourhood, started into air upon them. The wind is said in this case, first to have discomposed his machine, bringing down, also, this adventurer; he fell precipitantly, broke both his legs, and died from the consequences.

5. To lord Bacon, the prophet of art, as Walpole calls him, has been attributed the first suggestion of the true theory of balloons. But the value of his remarks upon this subject has been overated. The only clear passage in his works speaks of flying in the air," in the old plan of imitating birds; or, spreading feathers thin and close, and in great breadth, which, he says, will bear up

a great weight, being even laid, without tilting upon the sides.' And adds, the further extension of his experiment might be thought upon.' In another passage of his Natural History, entitled, Experiment Solitary, touching the flying of unequal bodies in air, he says, "Let there be a body of unequal weight, (as of wood and lead, or bone and lead) if you throw it from you with the light end forward, it will turn, and the weightier end will recover to be forwards, unless the body be over long. The cause is, that the more dense body hath a more violent pressure of the parts from the first impulsion, which is the cause (though not heretofore found out, as hath been often said) of all violent motions: And when the hinder part moveth swifter (for that it less endureth pressure of parts) than the forward part can make way for it, it must needs be that the body turn over; for (turned) it can more easily draw forward the lighter part."

We see in this passage no hint at the scientific theory of aeronautics; it is simply an obscure speculation on the quantum of resistance which a body meets with in passing through the air :here is not a word of the power of rising in it.

6. But in the fourteenth century that theory is recorded in the writing of Albert of Saxony, an Augustin inonk, and a commentator on Aristotle. Following the old notion of fire floating above the atmosphere of the earth; he suggests, that if any being could bring down a quantity of that light ethereal air that swims above our atmosphere, and inclose it in a ball or vessel, the vessel might be raised, and kept suspended in common air, at any height. This suggestion rested in perfect dormancy until the beginning of the seventeenth century, when Francis Mendoza, a jesuit of Portugal, maintained that the combustibility of fire was no objection to its being made to ascend in proper vehicles, as its extreme laxity and the exclusion of air would preserve it from inflammation. He died at Lyons A.D. 1626. At about the same period Caspar Schott, also a jesuit, published this theory in Germany.

7. In 1670 all the ancient speculations about artificial wings whereby a man might fly as well as a bird, were refuted by Borelli in his treatise De Motu Animalium. In this work, from a comparison between the power of the muscles which move the wings of a bird, and those which move the arms of a man, he demonstrates, that the latter are utterly insufficient to strike the air with such force as to raise him from the ground.

8. In the year 1672, Bishop Wilkins published his Discovery of the New World, in which he certainly seems to have conceived the idea of raising bodies into the atmosphere by filling them with rarified air. This, however, he did not pursue, but rested his hopes upon mechanical motions, to be accomplished by human strength, or by springs, &c. which have been proved incapable of answering any useful purpose.

9. The jesuit, Francis Lana, his contemporary, proposed to exhaust_hollow balls of metal, of their air, (See Plate I. ERONAUTICS,) and thus occasion them to ascend. But though the theory was unexceptionable, the means he suggested were insufficient to the end for a vessel