opinion, which, in a theoretical point of view, confirms the theorem of Melanderhielm.

To attempt to combat this theory, adds our author, would have the effect of entangling us in a multitude of inextricable difficulties; for we must then affirm that ether and air have no communication together; that consequently they cannot mix, and that there is between them a kind of barrier, as if our earth was enclosed in a globe of hollow glass yet we know that all gases mingle together, which, moreover, must happen from the pressure of our air upon ether, and, reciprocally, on account of the rapid motion of the earth. It is to this pressure that M. de Zach attributes the diurnal oscillations of the barometer, observed at the equator by Humboldt. We should likewise be obliged to affirm, that as the air of planets is essentially different from ether, there can be no affinity between them, and consequently that nobody can burn in ether for want of oxygen, a conclusion not warranted by observations, since shooting stars and meteors burn and shine at a height at which in general the presence of atmospheric air is not supposed. For example, in 1795, Schroeter saw, with his reflecting telescope of 20 feet long, a shooting star, the height of which he estimated at more than four millions of miles. If then it be admitted that each body of the universe, by the influence of a weight proportioned to its bulk, forms out of ether, the atmosphere by which it is surrounded, then the moon must also borrow from ether its portion, which becomes condensed and forms its atmosphere. The existence of water in the lunar atmosphere can no longer be questioned, for clouds have been seen upon its surface, as is proved by the almost innumerable observations of Schroeter, to whose work the Doctor refers for more extensive details.

Organised Beings in the Moon. It is a remarkable circumstance, observes M. Gruithuisen, that all those who only take what may be termed a cursory survey of the moon through a telescope, consider it as a desert and globe, upon which nothing lives or grows: on the contrary, others who have explored its surface for many years, speak of it, as if organised beings could not fail to exist there.

Shroter conjectures the existence of a town towards the north of murius (a lunar spot), and the canals which are observable towards hyginus (another spot), and which, after disappearing in some places, are again perceived in others (a thing, says Dr. G. of which I have convinced myself), appear to him very advantageous for the commerce of the Selenites: finally, he represents a part of the spot named mare imbrium to be as fertile as Campania.

The ancients supposed the moon to be inhabited. Orpheus, Anaxagoras, Xenophon, and Pythagoras, are of this opinion. Their strength of reasoning compensated, in this instance, for their want of telescopes: even Plutarch entertained the idea, that the obscure places on the moon's surface were seas, which could not reflect the light of the sun. More recently, Kepler, Duhamel, and many others have been of the same way of thinking respecting the existence of the Selenites. Indeed, so general has this sentiment been, that even the American savages have believed the moon to be inhabited.

In latter times, some persons have considered the too great rarefaction of the air as an insuperable obstacle to peopling the moon. Without doubt, says our author, this circumstance would not fail to alarm more than one philosopher of a delicate constitution, particu-larly when he knows that neither raisins nor apricots are to be found even on the Chimboraço. Others, on the contrary, have not forgotten that Mr. Guy-Lussac ascended, with his balloon, to a height greater by 2000 feet than the height of that mountain. So that an inhabitant of our globe, if placed in the lowest regions of the moon, might find himself very ill at his ease, but not so much so as to cause his death.

He

While speaking of the inhabitants of the moon, we may observe, that some theorists have affirmed that no animated beings could exist on that planet, but such as were capable of eating stones, doing without drink, living on a scanty supply of air, and supporting the extremes of heat and cold. These particulars, adds Mr. Guithuisen, may be considered as a summing up of all the doubts that have arisen on the question whether the planets are habitable or not. then discusses each of these points. He thinks he can confidently affirm that the moon has vegetables and animals to serve for food to its inhabitants: he even goes so far as to indicate some of their genera and species. In the absence of wine, he continues, the Selenites have water, so that they possess the means of quenching their thirst. They are likewise supplied with air in more than sufficient quantity, only that this air is extremely rarefied. If we admit of lakes and seas in the moon, why should they not contain shell and other fish, and amphibious beings? And that man can accustom himself to a highly rarefied atmosphere, has been shewn by the aerial ascent of M. Guy-Lussac, already referred to. According to Humboldt, the atmosphere supports a column of quicksilver of only twenty inches at Quito; of eighteen inches at Micuipampa, and of seventeen inches in the latitude of Antisana, all inhabited places upon the earth, notwithstanding this rarefaction. Lastly, the Selenites can face the cold and heat with the assistance of fire, which they have the means of procuring in the former case; and in the latter, by means of the deep caverns, in whose coolness they can obtain refuge from the heat.

Waters in the Moon. By these, says our author, I understand all the springs, rivers, lakes, and seas. After having collected and discussed at great length all the facts calculated to illustrate the subject, he thinks he has a right to ask, who can now bring forward any probable argument against the existence of lakes in the moon? But, he adds, lakes presuppose rivers, or at least simple rivulets or springs, their existence is then sufficiently demonstrated.

Of the Lunar Structure. The interior structure of the moon is probably not different from that which is common to all the bodies of the universe; namely, concentric beds formed by the accumulation of successive strata.

Of the Exterior Structure or Constitution. This consists properly in

the chains of mountains; the caverns, the declivities and the acclivities are immediate consequences of this disposition.

We shall only add a few words relative to the lithographical map which Doctor Gruithuisen has attached to his work, for the purpose of facilitating the discovery of the points, which he more particularly wishes to designate upon the face of the moon. To accomplish this, he indicates their situation by their distance from two lines, which may be said to represent the equator and the first meridian of the moon, which we consider to be a felicitous and useful imitation of terrestrial longitudes and latitudes.

On Professor Struve's Observations to determine the Parallax of the fixed Stars.

Of the various attempts to discover the parallax of the fixed stars, the observations of Professor Struve must be regarded as among the best, and most judicious.

His object is, by means of an excellent transit instrument furnished with seven wires, to determine the sum of the parallaxes of several fixed stars, differing nearly 12 hours in right ascension from each other.

The results which he obtains, seem to verify a remark made by Mr. Pond, that in proportion as any improvement takes place either in our instruments or our processes, the resulting parallax becomes proportionally less.

Of fourteen sets of opposite stars thus compared, Mr. Struve finds seven, which give the parallax negative; this circumstance alone should suggest great caution in attributing to the effects of parallax the small positive quantities that are derived from the remaining seven. Mr. Struve however is inclined to assign 0".16 of space as the parallax of Ursa Minoris, and 0".45 for the sum of the parallaxes of a Cigni, and Ursa Majoris. His learned coadjutor, M. Walbeck, who, it appears, has undertaken the calculations, is disposed to attribute the greatest portion of this parallax to the smaller star; a circumstance so improbable requires very strong evidence for its support.

If we take the mean of the fourteen results as relating generally to stars from the 1st to the 4th magnitude, it will appear that the mean sum of the parallaxes of two opposite stars is equal to 0.036 of space, or the parallax of a single star equal to 0".018.

If any reliance can be placed on these observations, every attempt to determine the parallax of these stars in declination must be entirely hopeless; since in this case we can only measure the shorter axis of the Ellipse, and the uncertainty of refraction must amount, at least, to twenty times the quantity we are in search of.

On the Method of Determining the Figure of the Earth by the Pendulum.

THE method of determining the figure of the earth by means of the pendulum, depends upon the variation of gravity at the earth's surface. This subtile and pervading power, tends to communicate to bodies exposed to its influence equal velocities in equal times. One of the modifications of this action is the oscillation of the pendulum, which is of longer or shorter duration, according to the energy of the attractive force, and the square root of the length of the pendulum. If the earth were an exact sphere, destitute of the motion of rotation, and possessing the same density throughout its whole mass, the force of gravity, by which bodies at its surface are drawn towards the centre, would be uniform, and invariable in every latitude. But the elliptical form of the earth destroys this uniformity, and causes the attractive force at the poles to preponderate over that at the equator. This inequality in the force, by which bodies at the surface of the earth retain their positions, is augmented by the diurnal rotation, which, by centrifugal tendency, impresses a greater disposition on bodies to recede from the centre of the earth at the equator than at the poles, where its effects cease to be felt. By the joint operation of these two causes, one of which acts with a force proportional to the square of the sine of the latitude, a sensible difference ought to be observed in the velocity acquired by heavy bodies, in falling through the same space, as we advance from the equator to the poles. An important relation between the time of the vibration of a pendulum, and that of the descent of a heavy body, according to which the lengths of pendulums, vibrating ischronously, are directly as the force of gravity, enables us to submit this conclusion to the test of experiment. Newton long ago demonstrated, that if the earth were perfectly homogeneous, the same fraction, viz. 230, would express both the compression of the terrestrial ellipsoid, and the increase of gravity from the equator to the poles. This conclusion, which was deduced from the supposition of an uniform density, was afterwards modified, with singular address, by Clairaut, who showed, that the two fractions expressing the compression, and the increase of grvity, though not exactly equal, must always together amount to 230. Assuming the compression, therefore, to be equal to 12, the increase of gravity from the equator to the poles, or the indication of that increase, as given by the length of the pendulum, should be 23-312, or 12 nearly. The correctness of this conclusion, if not completely established, is, at least, to a certain extent, confirmed, by the experiments which have been made with the pendulum in different latitudes. La Place having selected fifteen of the best of these observations, and applied to them the necessary corrections, on account of the resistance of the air, difference of temperature, and elevation above the level of the sea, deduced the following results, in which the length of the pendulum at Paris is considered to be unity.

f

1

230⚫

The above results indicate obviously an increase of the force of gravity from the equator towards the poles. La Place has shewn that, in whatever way they are combined, it is impossible to avoid an error of less than 00018, on the hypothesis of the variation of gravity at the surface of the earth increasing as the squares of the sines of the latitude from the equator to the poles. The expression for the ellipticity, which connects best the different equations of condition, is a result which accords in a very remarkable manner with the compression deduced from the measures of the French mathematicians in France, and at the equator.

335.789

pro

It may be inferred from these experiments with the pendulum, that the compression of the earth is greater than is compatible with the supposition of an uniform density. The same anomalies, too, which are discernible in the measurement of a degree of the meridian, and which are undoubtedly owing to the dissimilar structure of the globe, may be traced in the results of these experiments. The beautiful perty of the pendulum, first discovered by Huggens, that the centre of oscillation and the point of suspension, are interchangeable with each other, and which has been so happily applied by Captain Kater, to determine the length of the seconds' pendulum, renders this mechanical contrivance infinitely better fitted to ascertain the true figure of the earth, than the complicated methods which were formerly employed for the same purpose. The facility with which the observations may be made, and the certainty of the results with which they are attended, may be expected to furnish much interesting information, not only with respect to the general form of the globe, but also with respect to its structure and composition in particular situations.