fibration of the moon, the precise limits of her Juminous rays, and ber diameter, together with the magnifying power of the astronomical instrument employed.

It must be confessed that the means within his reach were of the most ample kind: his thirteen and twenty-seven feet reflectors magnified two and three thousand times and even more; but finding that he gained in point of clearness in the image in most of his observations when he used eyeglasses of less power, he preferred an eye-glass which magnified 130 times for his thirteen feet telescope, and an eye-glass of 180 for his seven and twenty feet instrument.

In order to give an idea of the first three sections, which contain in twenty-eight chapters a very precise description of some particular regions of the moon, we shall present our readers with the following analysis.

The author informs us, that in order to examine the surface of the moon with advantage, he confined his enquiries to very small portions of the planet at a time which were illuminated under a very small angle of light. In this way he frequently discovered incomparably more with glasses of small power than with the most powerful instruments, when taking observations under much larger angles of illumination, i. e. when the rays of the sun arrive under a greater altitude at any given point in the moon.

It may sometimes happen that one astronomer does not see objects in the same light as another, although their instruments and the other circumstances were precisely similar: this does not always arise from the effects of the different angles of illumination under which the object is discover ed, and the very different reflections which frequently result; but may also be ascribed to the accidental variations of the atmosphere of the moon, which are very frequent, or to other causes which must be investigated by actual observations of the planet itself. It has also more than once happened that M. Schroeter himself saw objects quite differently at one time and at another, and sometimes even he lost sight of them altogether, although he employed instruments of the greatest magnifying power. He cites as an example of this anomaly, an observation upon the spot of "Gassendi, which he has represented by two draw ings of different dates. He remarks a great number of these accidental variations observed at various points in the moon's disk, and takes occasien to offer some conjectures, which are perhaps worthy of being repeated.

On the 1st November, 1791, for instance, he saw the crater which forms the centre of Possidonius under the appearance of a tolerably uniform circular plain of a greyish colour, without any darker shade, while the seven craters surrounding it were very deeply shaded. Next day in the evening the same object, seen with the same telescope, shewed itself as a profound crater, with obscure shades, although, if it could have been judged by the direction of the solar rays upon this part of the moon, the shadows ought to have appeared longer and stronger that evening than the day before. Nothing but an accidental cause could have altered the apparent form of the crater in twenty-four hours, whether we attribute this accident to a change in the atmosphere of the moon, or to a fermentation in its interior, or to the actions of some animated beings who inhabit it. In this same region of Possidonius, M. Schroeter saw with the greatest precision on the 4th of June,

1794, in a clear and calm day, five new objects: whether these were new craters, or chains of mountains which he had not seen before, he never observed them since.

On the other hand, he could not recognise with the twenty-seven feet telescope the crater which he had previously and repeatedly observed with the seven feet telescope; this he attributes to a variation in the atmosphere of the moon. He also observed with a thirteen feet reflector a new production, which unexpectedly appeared in a very distinct manner, in a crater, on the 6th of February, 1797, although in the course of nine years of anterior observations made with the best instruments, he had never discovered the least trace of such a phenomenon. This new production had in all probability made its appearance between the 12th of October, 1796, and the 6th of February, 1797. Subsequent to this last period, it had generally been visible under very different, and sometimes unfavourable angles of illumination; and yet other variable appearances were exhibited, particularly subsequent to the 4th of July, 1797, at which period this new crater was confounded in a mass of atmospheric fermentation, and perhaps new eruptions ensued.

In order to render more sensible the different forms under which the various objects in the moon may present themselves to the astronomical observer, and according to the accidental variations of the atmosphere of this planet, the author represents the landscape around Lilienthal, the place of his residence, as seen from the moon in the month of July, when the inhabitants of these euvirons burn the wrack off their fields, and when a thick smoke is spread over the ground. An observer placed in the moon at this period would see a grey envelop extended over that part of the north of Germany, an appearance which would not take place under any other circumstances. M. Schroeter is of opinion, that the crater of Possidonius, as already mentioned, having appeared grey on the 1st of November, and of an obscure black next day, may be ascribed to similar circumstances. In this former volume he had spoken of a great number of luminous points in the obscure hemisphere of the moon, subject to variations which had not for their only cause the differences in the reflection of the light of the earth. All these facts have now been confirmed by the help of great reflectors, and particularly in the luminous spots Aristarchus, Manilius, and Menelaus, in which the author has found at certain times distinct objects, and at others has not been able to discover even the objects themselves. The following luminous appearances appear to be somewhat remarkable: on the 2d of April, 1794, at eight o'clock in the evening, the obscure part of the disk being very distinctly visible, M. Schroeter discovered near the western boundaries of the sea of vapours (mare vaporum), in opposition to the dull light of the other parts, a luminous point extremely brilliant, which equalled a fixed star in lustre, and which the author had never perceived at that particular spot. It was evident, at the first glance, that this light could not have been reflected from the earth, and, in fact, in half an hour or less this brilliant point vanished so completely that it could no longer be recognized, and the author frequently afterwards conjectured that it no longer existed in the same place, but a similar point shewed itself towards the west. The kind of meteor which thus vanished is an appendage to the phenomenon observed long before in the

spot of Plato in the Alps of the moon, when upon the 26th of September, 1788, M. Schroeter feebly discerned a similar luminous point, and found that it began to be less and less discernible until it disappeared, nor did he see it again for twelve years. This former phenomenon in the Alps of the moon may have been the effect of a very active effort of nature, and the new phenomenon which happened in the milder temperature of the sea of vapours may rather be considered as the effect of a voluntary or involuntary action of the inhabitants of the moon. An illumination at London; a city on fire; the flashes of gunpowder from a besieged fortress, seen from the moon with M. Schroeter's reflectors, would present a spectacle similar to these luminous evanescent appearances seen from the earth upon the surface of its satellite. The Sea of the Crisis, in particular, which is one of the most remarkable places upon the surface of the moon, is thickly strewed with luminous points, which seem to belong to a plain abounding in asperities, natural or artificial."

Besides several high mountains, the exact measurements of which are here given, the author has discovered in several places of the moon, for instance in Possidonius, small elevations which are nearly fifty feet in height, and even less; an ianumerable quantity of similar asperities is also to be found at a small distance from Marius. These eminences are not constantly visible, and their form is variable.

In the sea of vapours near Plato, and in other places, M. Schroeter discovered deep furrows, or a kind of long narrow valley resembling a canal. This phenomenon extends for seventy geographic miles into the sea of vapours. We are acquainted with no sublunary valley of so great a length. It is somewhat singular that this valley stretches over inequalities of mountains and craters in such a manner, that the upper ridge of these eminences is intersected by the furrow or valley in question. Can this be a production of nature, or of the free agency of animated beings? Such is the question put by M. Schroeter to his readers; and his observations seem to place it beyond a doubt that the moon has not at its surface any fluid so dense as the water of our earth; and he has also apparently demonstrated that his favourite planet has Do considerable rivers, nor natural basins which serve to contain water, as in this sublunary world; but it does not follow from all this that the moon is a chalky body entirely dry; these long vallies or canals may perhaps contain rivers which have the same relative density to the subtle atmosphere of the moon, that is observed between water and our terrestrial atmosphere. Thus, in a certain sense, we may say that the moon has its rivers Plata and Amazon. Throughout these lunar Alps, (a chain of mountains equally continuous with those of Europe) we find the valley or furrow above mentioned stretching like a narrow pass, as if a violent convulsion of nature had cleft the mountains in a straight line.

In the fourth section, which contains observaticas upon the structure of the moon, the first chapter treats of the eminences and depression of that planet, and of its craters and vallies in general. The highest mountains, as the author had formerly estimated, are five times higher than the mountains of our globe, keeping in view the relative diameters of the two planets. The highest mountains of Venus and Mercury are, with respect to the mountains in the moon, nearly in the proportion of the relative diameters of these pla

nets. The greatest height, according to the former observations of M. Schroeter, was to be met with in some peaks of the chains of mountains known by the name of Leibnitz and Dorfelsh, towards the south pole of the moon; and in the eastern parts of the southern hemisphere, in the mountains D'Alembert and De Rook. The height of the latter is from 24 to 25,000 feet, and none so high have been as yet observed in the northern hemisphere. The cclipses of the sun afford opportunities of observing directly the vertical altitudes of the mountains of the moon which are exhibited upon its obscure edge. An observation in these circumstances succeeded with the author at the time of the great eclipse of the sun, Septemtember, 1793. Immediately after its commencement he observed some summits of mountains projecting from the edge of the moon's disk, which, in their vertical height alone, and in the extent to which they were seen (for the lower extremities were lost in obscurity), must have been 3.000 geographical miles high. During this remarkable eclipse, Herschel also discovered two summits of mountains which were projected upon the edge of the sun. The spherical form of the moon projected upon this edge was remarked by M. Schroeter and by all his pupils with the utmost precision; at the distance of one minute from the limb, what was observable of this spherical form gradually disappeared: a phenomenon which M. Schroeter endeavours to account for in another place by remarking, that the light of the earth was considerably increased by the solar penumbra, and by the crepusculum.

The depth of some craters of certain hollows, which are not circular, extends, according to the author, to the depth of three quarters of a mile. A short distance from the high mountain Rook, we find a hollow called Christopher Milius, the vertical depth of which is at least 15 or 16,000 feet. The Chimboraco of our globe might be wholly swallowed up in this cavity. Craters in general are formed by eruptions from the interior; they are empty basins, from which the mass that surrounds them in the form of a ring has been vomited; but in the moon there are cavities of another kind, such as those of Milius and others already named, presenting irregularities of a circular form in the edges of the moon, between the interstices of which we can see the clear sky; there are some parts in the moon which are sunk by some powers of nature, vallies hollowed out, not merely upon the surface of that planet, but dug as it were into its mass: i. e. greatly below its mean surface. The fixed stars we perceive in the vicinity of these bollows of the moon may for this reason appear sooner or later by a few seconds in their emersions or immersions, than when they exist opposite those portions of the edge which are not irregular. The author, by referring to these sinuosities, ingeniously accounts for the pretended hole, which in the total eclipse of the sun on the 14th of June, 1778, was observed by admiral Ulloa. There could not possibly have been a volcano in the moon at that period, for it would have thrown out so glaring a light, that the luminous point must necessarily have been perceived in the black glass of the telescope upon the moon's disk. But the sun, when seen through a similar fissure, must have appeared as if seen through a hole, in the event of the direction of the fissure being oblique to that of the luminous ray, M. Schroeter, therefore, upon remarking that this fissure exists in the lunar region where the observation of Ulloa was

made, and that it exists in that place alone, gave it the name of the above admiral. M. Schroeter proceeds to draw the following inferences.

"The greatest eminences of 25,000 feet and upwards, and the deepest hollows of three quarters of a geographical mile in depth, are situated in the southern part of the moon; hence we may conclude from actual observations, that in the moon, as upon the earth, and in the planets Venus and Mercury, the southern hemisphere is generally the most unequal and irregular.

"As the gravitation at the surface of the moon is only, according to theory, about one-fifth of that which takes place on the earth, we may say that, with regard to the relative diameters of the two planets, the mountains of the moon are five times higher than those of the earth, as has been already remarked.

"In our globe earthquakes are extremely rare, and still more rarely do they produce complete eruptions, such as islands or new mountains: the solid mass of the earth opposing too much resistance to these formations. It is otherwise with the moon, where the gravity is five times less, and where explosive effects always meet with less opposition thence it follows, that the whole surface of the moon is almost always in a state of revoJution; explosions, earthquakes, and other convulsions, follow each other in dreadful successions. New objects appear and vanish almost while the astronomer has his eye at his telescope. Hence proceeds that innumerable heap of craters, the second formation encroaching upon the first, the third effacing the two former, while at each eruption the preceding one is overwhelmed even before it has attained its destination."

Our readers will at once perceive the total discrepancy between this terrific description of the revolutions of the lunar world, and the fantastic idea attempted to be inculcated by M. Schroeter that there are animated beings, with houses, paJaces, cathedrals, and tea-kettles, in the moon, as well as upon our planet. All these creatures of our astronomer's imagination must indeed be sui generis.

The fourth chapter of the second section is filled with enquiries into the atmosphere of the moon, its morning and evening crepusculum, the height and density of the air in that planet, &c. The author in his former volume had placed beyond a doubt the existence of an atmosphere which had been denied to that planet; he had mentioned a number of appearances in which some objects, in other respects identical, had appeared sometimes under one form, and at other times under another; while sometimes they were not visible at all: he had proved that this atmosphere of the moon, although much more subtle and transparent than ours, had the power of weakening, in a remarkable manner, the light of the sun descending under the lunar horizon; at which period, the summits of some mountains, being in this light on the obscure side of the moon, visibly threw out a lustre so much the more brilliant, as they were more distant from the edge of illumination, i. e. projected farther forward into the obscure part of the disk. All this, however, only gave rise to a conjecture as to a real refraction of the rays of light, whence there resulted a crepusculum upon the moon; but M. Schroeter has now converted this conjecture into a certainty by the observations contained in the present work. Ile has demonstrated not only that there is a crepusculum in the moon, but that we may measure

the extent of it, as well as the thickness and den sity of the layers of the finid which occasion it. The first complete observations were made by M. Schroeter upon this subject on the 24th of February, 1792, in the twilight of that night; the moon being then two days and a half old. With a Herschel telescope of seven feet, and magnifying seventy-four times only, he discovered in the obscure part of the moon some places illuminated with a dull greyish light, very near to other obscure parts which did not become visible until some time afterwards; a heavy and evidently crepuscular lustre enlightened the coufines of the obscure edge of the planet, stretching into the points of its two horns, and this lustre spread out in the form of a pyramid, the summit of which was insensibly confounded with the light sent from the earth into the obscure part of the moon. The projection of this shining part was then 1' 10" in length, and 2" in breadth.

He then concludes that this crepusculum of the moon can be better observed two or three days before and after the new moon, and in spring and autumn during the short crepuscula of the earth, and the greatest height of the moon in the horizon. Our author, therefore, fixed upon the moment of the smallest elongations of the moon, twenty-eight hours and a half after its being renewed, with a twenty-seven feet reflector. Hevelius had not been able to observe the moon until at least forty hours after the conjunction. By a geometrical process M. Schroeter estimated the extent of the lunar crepusculum, according to the distance comprehended between the limits of this crepusculum and the point of the horns, and he found by several observations that it extends over an are of 24 degrees of the moon's circumference. Or rather, taking the medium of twenty-two observations made during eight years, he estimates this extent more exactly at 2° 38′ 56′′, but it sometimes amounted to 3° 6' 44". Several favourable circumstances must combine in order to observe this appearance. The author has sometimes perceived it merely in the prolongation of one of the two horns; at other times it was invisible, because apparently there were mountains which intercepted the light.

There remained a doubt whether this crepuscular light was or was not a consequence of the penumbra, or perhaps the effect of the immediate reflection of the solar rays, by means of some greyish plains in the moon. The author endeavours to resolve this doubt in a manner which sets at defiance the possibility of any illusion. Upon the whole, it is proper to say of this chapter upon the lunar atmosphere, that it contains the result of many years fatiguing observations, which will hand down the name of M. Schroeter as an honour to the age in which he lived.

If we adopt, in the calculation of these observations, the same principles by which La Hire has determined the height of our terrestrial atmosphere, by extending to 38,000 feet the height at which the atmosphere ceases to reflect the light in a sensible mauner, or to 34,500, if the limit of refraction is in question, we find that the analogous limit in the atmosphere of the moon rises only 1,404 feet, according to the maximum of extent observed by M. Schroeter, namely, 3o 6′ 44′′. But this height is solely that of the lunar crepusculum visible to us. The author estimates at 78 feet, the height of the strata of the lunar air which may occasion a crepusculum upon the same plaFrom these data the author has theoretically

net.

enquired what ought to be the relative density of the atmosphere of the earth and of the moon, and he has found that the atmosphere of the latter ought to be twenty-nine times less dense than ours, and at the moment when the work was put to press, Dr. Melanderhielm, of Stockholm, wrote to M. Schroeter that he had ascertained that the density of the atmosphere of two planets should in general be as the square of the power of gravitation at their surface; now according to Newton, the gravity at the surface of the moon is to the same power upon the earth as 2,83: 15,10, or as I to 5.33. According to this theorem, the density of the air of the moon should therefore be as the square of 5,33, or 28,40 times less than that of the air of the earth; this differs very little from the result incontestably found by M. Schroeter after a most fatiguing and intricate train of experi

ments.

According to the same principles, we ought to find the refraction at the surface of the moon to be 28 or 29 times less than at the surface of the earth.

M. Schroeter applies his discoveries upon the Jaar atmosphere to the occultations of stars by this satellite. As the height of the inferior strata of the air, which can still break the rays of light in a manner sensible to us, does not exceed 648 yards, a quantity which viewed from the earth, only passes from the edge of the moon o" 36 of a second, the weakening of the light of a fixed star entering into this atmosphere could not, if it were sensible, be perceived except during a quarter of a second, the time which the moon takes to travel of a second of a degree in her orbit. Now the lustre of stars of the first, second, and third magnitude, is too strong to admit of our observing any diminution for so short a period. If it be a planet which undergoes the occultation, its diminution of light on arriving at the disk may proceed from the graduated occultation of its apparent diameter. This system agrees with twenty occultations described in detail by the author.

The most brilliant fixed stars, and the planets, exhibit no diminution of light in this case; it is only remarked from time to time in the minute stars, not visible to the naked eye, and these last only undergo this obscuring of their light, when by chance they come out or enter opposite to the summit of a mountain of mean altitude, when the air of the moon, less dense, cannot any longer cause any sensible refraction of the rays coming from the star. There may be exceptions when the star which enters corresponds to the declivity of a very high mountain; and entering also obliquely, it seems to lose its light gradually; a dimination which, according to the author's observations, in a certain case (the only one of the kind), may be remarked during seven or eight seconds, On this occasion, which furnishes a kind of micrometrical measurement applicable to the fixed stars, the anthor found their diameter very small. The diameter of Aldebaran, according to the time employed in its immersion upon the edge of the moon, appeared to him to be between and of a second; the diameter of the star 30, and the Pisces 33, appeared to be more than 4 of a second, The other fixed stars suddenly disappeared, without the phenomenon having any sensible dura

In the third chapter of the fourth section, M, Schroeter gives a kind of recapitulation. To this chapter an engraving is attached, which exhibits in a distinct manner the relation of the vertical height

of the densest atmosphere of the moon, with the height of the mountains of that planet, which have been measured, and with the depth of the craters, and other cavities or hollows. In the first figure of this plate are represented the lowest chains of mountains, 16 or 18 yards high; on the second, the mountains with circular edges containing a plain or a crater; in the third, the higher mountains placed above some mountains with circular edges; in the fourth, the central mountains or those which are seen in the midst of craters of mountains, with circular edges; in the fifth, the other isolated mountains from 50 to 25,000 feet of vertical height, the craters and other cavities of the moon, from 602 to 50,80 yards in depth. All these particulars are represented upon the same scale on which 200 yards correspond to a decimal line. The same table contains comparisons between the high est mountains of the moon, and those of the earth, Venus, and Mercury; with the references betweer. the altitudes of the crepuscular strata of the moon, the earth, and Venus. We see at a single glance, according to this table, that the craters and the fissures of the edges are for the most part proportionally deeper, according as the atmosphere is higher, and that consequently the air of the moon must attain a certain maximum of density in their interior; moreover that the accidental variations of the atmosphere cannot take place, except in the region of the lower mountains of the moon, and not at the summits of the high chains; these last being far above the densest strata. In fact, the author has most frequently observed these accidental variations in the lower regions; as, for instance, in the sea of the Crises, in Cleomedes Possidonius, Gassendi, &c. In this atmospherical constitution of trifling density, we ought not to be astonished if there be continually developed so many fermentable matters from the interior of the moon, and if we see no atmospherical productious like our clouds, and none of those regular easterly or westerly winds which we find upon our own earth, and upon Venus, Mars, and perhaps Saturn. The atmosphere of the moon seems in general to be too subtle for the existence of any winds which can be properly so called. Slight atmospherical vapours alone always cover some low and contracted plains, and in all cases those which constitute the inferior level of the moon.

Of the harvest-moon.-It is remarkable that the moon, during the week in which she is full about the time of harvest, rises sooner after sun-setting than she does in any other full-moon week in the year. By this means she affords an immediate supply of light after sun-set, which is very beneficial for the harvest and gathering in the fruits of the earth: and hence this full moon is distinguished from all the others in the year, by calling it the harvest-moon.

To conceive the reason of this phenomenon; it may first be considered, that the moon is always opposite to the sun when she is full; that she is full in the signs Pisces and Aries in our harvest months, those being the signs opposite to Virgo and Libra, the signs occupied by the sun about the same season; and because those parts of the ecliptic rise in a shorter space of time than others, as may easily be shewn and illustrated by the celestial globe: consequently, when the moon is about her full in harvest, she rises with less difference of time, or more immediately after sun-set, than when she is full at other seasons of the year.

In our winter, the moon is in Pisces and Aries about the time of her first quarter, when she rises

about noon; but her rising is not then noticed, because the sun is above the horizon.

In spring, the moon is in Pisces and Aries about the time of her change; at which time, as she gives no light, and rises with the sun, her rising cannot be perceived.

In summer, the moon is in Pisces and Aries about the time of her last quarter; and then, as she is on the decrease, and rises not till midnight, her rising usually passes unobserved.

But in autumn, the moon is in Pisces and Aries at the time of her full, and rises soon after sun-set for several evenings successively; which makes her regular rising very conspicuous at that time of the

year.

And this would always be the case, if the moon's orbit lay in the plane of the ecliptic. But as her orbit makes an angle of 5° 18' with the ecliptic, and crosses it only in the two opposite points called the nodes, her rising when in Pisces and Aries will sometimes not differ above 1 h. 40 min. through the whole of seven days; and at other times, in the same two signs she will differ three hours and a half in the time of her rising in a week, according to the different positions of the nodes with respect to these signs; which positions are constantly changing, because the nodes go backward through the whole ecliptic in 18 years 225 days.

This revolution of the nodes will cause the harvest moons to go through a whole course of the most and least beneficial states, with respect to the harvest, every 19 years. The following table shews "in what years the harvest-moons are least beneficial as to the times of their rising, and in what years they are most beneficial, from the year 1790 to 1861; the column of years under the letter L are those in which the harvest-moons are least of all beneficial, because they fall about the descending node; and those under the letter M are the most of all beneficial, because they fall' about the ascending node.

Harvest Moons.

L M L M L M L M 1790 1793 1807 1816 1826 1835 1844 1853 1791 1799 1808 1817 1827 1836 1845 1854 1792 1800 1809 1818 1828 1837 1846 1855 1793 1801 1810 1819 1829 1838 1847 1856 1794 1802 1811 1820 1830 1839 1848 1857 1795 1803 1812 1821 1831 1840 1849 1858 1796 1804 1813 1822 1832 1841 1850 1859 1797 1805 1814 1823 1833 1842 1851 1860

1806 1815 1824 1834 1843 1852 1861 1825

Acceleration of the Moon. See ACCELERATION. Horizontal Moon.-It is a celebrated phenomenon that the moon appears larger in the horizon than in the meridian; whereas, from its being further from us in the former case than in the latter, it subtends a less angle when in the horizon. It is perhaps not easy to give a satisfactory answer to this deception. Gassendus thought, that as the moon was less bright in the horizon than in the meridian, we looked at it in the former situation, with a greater pupil of the eye, and therefore it appeared larger. But this is not agreeable to the principles of optics, since the magnitude of the image upon the retina of the eye does not depend upon the size of the pupil. Des Cartes thought that the moon appeared largest in the horizon, because when comparing its distance with the intermediate objects it appeared then furthest off; and as we judge its distance greater in that situation, we, of course, think it larger, supposing that it sub

tends the same angle. Dr. Berkeley accounts for it thus: faintness suggests the idea of greater distance; the moon appearing faintest in the horizon, suggests the idea of greater distance; and, suppos ing the angle the same, that must suggest the idea of a greater tangible object. He does not suppose the visible extension to be greater, but that the idea of a greater tangible extension is suggested, by the alteration of the visible extension. He says, 1. That which suggests the idea of greater magnitude, must be something perceived; for that which is not perceived can produce no effect. 2. It must be something which is variable, because the moon does not always appear of the same magnitude in the horizon. 3. It cannot lie in the intermediate objects, they remaining the same; also, when these objects are excluded from sight, it makes no alteration. 4. It cannot be the visible magnitude, because that is least in the horizon. The cause, therefore, must lie in the visible appearance, which proceeds from the greater paucity of rays coming to the eye, producing faintness. Mr. Rowning supposes, that the moon appears furthest from us in the horizon, because the portion of the sky which we see appears not an entire hemisphere, but only a portion of one; and hence, we judge the moon to be further from us in the horizon, and therefore larger. Dr. Smith, in his optics, gives the same reason. The same circumstances take place in the sun. Also, if we take two stars near each other in the horizon, and two other stars near the zenith at the same angular distance, the two former will appear at a much greater distance from each other than the two latter. On this account, people are, in general, much deceived in estimating the altitudes of the heavenly bodies above the horizon, judging them to be much greater than they are. The lower part of a rainbow also appears much wider than the upper part; and this may be considered as an argument that the phenomenon cannot depend entirely upon the greater degree of faintness of the object when in the horizon, because the lower part of the bow frequently appears brighter than the upper part, at the same time that it appears broader. Also, faintness can have no effect upon the angular distance of the stars; and as the difference of the apparent distance of the two stars, whose angular distance is the same in the horizon and the zenith, seems to be fully sufficient to account for the apparent variation of the moon's diameter in these situations, it may be doubtful whether the faintness of the object enters into any part of the cause.

MOON-BLINDNESS, a disorder in the eyes of a horse, so denominated from its having been thought to increase or decrease, according to the course of the moon.

This generally happens when a horse is turned five, coming six, at which time one eye becomes clouded, the eye-lids being swelled, and very often shut up; and a thin water generally runs from the diseased eye down the cheek, so sharp as sometimes to excoriate the skin. The veins of the temple, under the eye, and along the nose, are also turgid and full of blood, though sometimes it happens that the eye discharges but little.

Moon-blindness scarcely ever admits of a cure. It generally takes place while the horse is young, and sometimes has been attributed to the pain in cutting their teeth.

The inflammation in this disorder comes