De Luc's hypothesis, though he is far from embracing it as satisfactory, will sufficiently account for the relation above stated, by supposing that the column of phosphoric fluid is bent, previous to ignition, in the direction of the upper current; so that, when ignition commences, the luminous body moves towards the point from which that current then proceeds, and from which the lower current is afterwards to blow. It is a prognostication of wind, then, only in so far as it indicates a change that has already commenced in the higher regions of the atmosphere, but which has not yet taken place near the surface of the earth.

On Predicting the Weather.

FROM a very great number of meteorological observations, made in England between the years 1677 and 1789, Mr. Kirwan has deduced the following probable conjectures of the weather :

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 any easterly point, either on the 19th, 20th, or 21st of March, the succeeding summer is generally dry, four times in five.

3. 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 S. W., or W.S.W., on the 19th, 20th, 21st, or 22d of March, the succeeding summer is generally wet, four times in five.

To the above we shall add the following observations from the Encyclopedia Britannica.

1. A moist autumn, with a mild winter, is generally followed by a cold and dry spring, which greatly retards vegetation.

2. If the summer be remarkably rainy, it is probable that the ensuing winter will be severe; for the unusual evaporation will have carried off the heat of the earth. Wet summers are generally attended with an unusual quantity of seed on the white thorn and dogrose bushes. Hence the unusual fruitfulness of these shrubs is a sign of a severe winter.

3. The appearance of cranes, and birds of passage, early in autumn, announces a very severe winter; for it is a sign that it has already begun in the northern countries.

4. When it rains plentifully in May, it will rain but little in September, and vice versa.

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5. When the wind is S.W. during summer or autumn, and the temperature of the air unusually cold for the season, both to the feeling and the thermometer, with a low barometer, much rain is to be expected.

6. Violent temperatures, as storms or great rains, produce a sort of crisis in the atmosphere, which produces a constant temperature, good or bad, for some months.

7. A rainy winter predicts a sterile year; a severe autumn announces a windy winter.

On the Construction of the Heavens, by the late Sir W. Herschel.

IN a paper on this subject read before the Royal Society, Sir W. Herschel enumerates a great diversity of parts that enter into the construction of the heavens. The first species are insulated stars ; as such the author considers our sun, and all the brightest stars, which he supposes nearly out of the reach of mutual gravitation; for, stating the annual parallax of Sirius at 1", he calculates that Sirius and the sun, if left alone, would be 33 millions of years in falling together; and that the action of the stars of the milky way, as well as others, would tend to protract this time much more. Herschel conjectures that insulated stars alone are surrounded by planets. The next are binary sidereal systems, or double stars; from the great number of these which are visible in different parts of the heavens, and the frequent apparent equality of the two stars, Herschel calculates the very great improbability, that they should be at distances from each other at all comparable to those of the insulated stars: hence he infers, that they must be subjected to mutual gravitation, and can only preserve their relative distances by a periodical revolution round a common centre. In confirmation of this inference, he states that many double stars have actually changed their situation in a progressive course, the motion of some being direct, and of others retrograde. The proper motion of our sun does not appear to be of this kind, but to be rather the effect of some perturbations in the neighbouring systems. The same theory is next applied to triple, quadruple, and multiple systems of stars, and particular hypothetical cases are explained by diagrams. Some such cases, Herschel is fully persuaded, have a real existence in nature. The fourth species consists of clustering stars, and of the milky way; the stars thus disposed constitute masses, which appear brighter in the middle, and fainter towards the extremities, being perhaps collected in a spherical form. Groups of stars the author distinguishes from these by a want of apparent condensation about a centre of attraction and clusters of stars, by a much more complete compression near such a centre, so as to exhibit a mottled lustre, almost resembling a nucleus. The eighth species consists of nebulæ,

which probably differ from the three last species only in being much more remote; some of them, Herschel calculates, must be at so great a distance, that the rays of light must have been nearly two millions of years in travelling from them to our system. The stellar nebulæ, or stars with burs, form a distinct species. A milky nebulosity is next mentioned, which may in some cases resemble other nebulæ, but in others appear to be diffused, almost like a fluid: the author is not inclined to consider it as either resembling the zodiacal light of the sun, or of a phosphorescent nature. The tenth species is denominated nebulous stars; these are stars surrounded with a nebulosity like an atmosphere, of which the magnitude must be amazingly great; for the apparent diameter of one of them, described in the catalogue, was 3'. The planetary nebulæ are distinguished by their equable brightness, and circular form, while their light is still too faint to be produced by a single luminary of great dimensions. When they have bright central points, Herschel considers them as forming a twelfth species, and supposes them to be allied to the nebulous stars, which might approach to their nature, if their luminous atmospheres were very much condensed round the nucleus.

On the Use of the Telescope.

THE late Sir W. Herschel has remarked, that, "In order to seè well with telescopes, it is required that the temperature of the atmosphere and mirror should be uniform, and the air fraught with moisture." Thus a frost after a thaw, or a thaw after a frost, will impair the perfection of the focus: a telescope brought out of a warm room into a cold air, or even directed through an aperture of any kind, acts but imperfectly: windy weather is unfavourable to distinct vision, from a mixture of air of different temperatures: an aurora borealis sometimes affects the distinctness of the view, as well as the air ascending from the warm roof of a house dampness, fogs, and the neighbourhood of moisture, are very favourable to distinct vision with telescopes, except when a fog is so opaque as totally to intercept it. Sir W. Herschel remarks, that some of these obstacles are insuperable; but that the effect of heat may sometimes be remedied by the application of a heated body near the opposite surface of the mirror.

Sir W. also observes, that the central part of a mirror produces a greater aberration in the image of a fixed star than the whole mirror, and the whole mirror a greater aberration than an annular portion remote from the centre and that this is true of all good mirrors.*

* Some additional and useful remarks on the nature and application of the telescope, by the same author, will be found at page 31 of this work.

RIGHT ASCENSIONS and DECLINATIONS of the PRINCIPAL FIXED STARS, adapted to the Beginning of the YEAR 1824.

Remarks on different Hypotheses respecting the Moon, and various Phenomena of that Planet.

WE make no apology for submitting to our readers the subjoined extracts from a highly ingenious and interesting work, entitled SELENOGNOSTIC FRAGMENTS, published by Dr. Gruithuisen, whose name ranks deservedly high in the list of foreign astronomers. No body in the starry heavens, observes the Doctor, in his introduction, excites more general interest than the faithful satellite of the earth in fact, its surface presents, even to the naked eye, objects so varied, that it instantly inspires the spectator with a wish to inspect this unknown world, with the aid of a powerful telescope. But what especially prompts us to study the physical properties and constitution of the moon, is the expectation of discovering an analogy common to all the great bodies of the universe, with respect to their organization. This, he adds, is what has hitherto been the foundation of my celestial observations, being myself convinced that we shall never attain to any excellence in the study of geognosy, till we have discovered this analogy. It is with this intention that the author has surveyed, examined, and studied many chains of terrestrial mountains; and it is with this view that he publishes the particular appearances, which eight years observations have enabled him to remark upon the surface of the moon.

To render his work more intelligible to his readers, the Doctor has inserted a lithographic general map of this planet; for which purpose he has consulted Mayer's draught of the moon, and the special maps given by Schroeter in his Selenographic Fragments. Nor has he neglected to avail himself of his own observations. He likewise cites the lunar map of Lambert, and refers to a memoir of that philosopher in the first volume of the Berlin astronomical almanack.

Atmosphere of the Moon. Cassini, Louville, Bianchini, Carbone, Euler, Krüger, Boscovich, Ulloa, Dusejour, Wolf, and Halle, maintain the existence of a lunar atmosphere; while Mayer, Grandjean de Fouchy, De l'Isle, and De la Hire, deny it. Without dwelling upon the reasons and observations which, before the invention of achromatic telescopes have been alleged on both sides of the questions, Doctor Gruithuisen confines himself to the direct proofs drawn from the discoveries of Schroeter. The latter has calculated the elevation of the twilight observed by him in repeated observations on the increasing moon. This elevation agrees in a surprising manner with the theorem of Melanderhielm ; namely, that on the surface of planets the density of their atmospheres is in proportion to the squares of the weight of the bodies. This proportion had been suggested to Newton by that of the squares of weights on the surface of the moon, and the surface of the earth. In fact, this latter proportion being as 1 to 28'40, is almost equal to the result of Schroeter, who found that the lunar atmosphere is 28.94 times less dense than our own. Hevelius, Deluc, and many other philosophers, have thought that the air on the surface of planets was only ether condensed, and have considered ether, in its turn, as rarified air, an

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