thus present a singular contrast to each other, inasmuch as the darkness of the night in one is constantly relieved by the presence of our globe reflecting light, while the nocturnal darkness of the other is as constantly left to the illumination of the stars. In another respect also the moon contrasts strikingly with the earth. As she turns upon her axis but once a month, nearly fifteen days' sunlight will alternate with the same period of darkness, and thus the lunar day and night be each of that extent. The physical consequences of this arrangement will be-according to the analogy of terrestrial thingswinter and summer once a month of the fiercest description. During fifteen days' exposure to the sun an intense degree of heat will accumulate, and by fifteen days' deprivation of his beams an equal degree of cold be occasioned; and thus a temperature equal to the most fiery experienced upon the plains of India will alternate with one rivalling in severity that of ice-bound Spitzbergen. But it is a curious speculation, that it lies within the limits of possibility for a lunarian to travel as fast as the moon's motion upon her axis, and thus keep up with the day, living in perpetual sunshine. A ten miles per hour rate of locomotion would suffice for this, and a terrestrial dweller might accomplish that distance by a walk in half the time if transported to the moon, because of the feeble gravitation of bodies at her surface, for a body weighing six pounds at the earth would weigh only one pound at the moon. Consequently the same muscular force would there perform six times as much as on the earth. Linked in the bonds of a close and enduring relationship to the earth, the surmise is natural, that the two bodies dwelling together in unity harmonise in their physical constitution. We are apt to transfer to the lunar mansion the features of our terrestrial residence—its diversities of ebbing ocean and stable continent—hill, dale, and plain— wood, brook, and flower-stormy wind and balmy breeze. But a course of observation diligently pursued with reference to the satellite corrects some of these imaginings, and discloses striking points of discordance with those of agreement. Whether the lunar globe has any gaseous covering, like that which supplies us with the breath of life, is a subject upon which there has been considerable conflict of opinion. Those who deny the existence of any atmosphere depend chiefly upon the equable brightness of the moon's disk, which, it is argued, would not be the case if she were surrounded with one like ours, so variable in its density, and so often charged with immense masses of cloud and vapour. It is also pleaded, that when the moon occults a planet or fixed star, there is no perceptible diminution of light and alteration of colour before complete obscuration, which there would be, owing to the influence of the lunar atmosphere, if there were one. An occultation of Jupiter took place on the 2d of January 1857, and was carefully observed with this reference. But there was not the slightest distortion of figure, diminution of light, or change of colour. Hevelius, however, and others, have observed variations in the brightness of the lunar orb, instances in which the moon and her spots have not appeared equally lucid and conspicuous, when the terrestrial skies have been free from cloud. Some have also thought that both Jupiter and Saturn undergo a perceptible change of figure when about to be occulted, and that fixed stars may be discovered in such circumstances to experience an evident diminution of light. Professor Nichol observes of the annular eclipse of May, 1836, that just before the rims of the sun and moon osculated, the light of the sun was mollified into lovely twilight, which he attributed to the effect of the moon's atmosphere. One fact is clear, and is admitted by all parties, that if there be a lunar atmosphere, it is of extreme tenuity and exceedingly small, considered by Laplace to be as attenuated as what is called the vacuum of an airpump, and estimated by Schroeter to be little more than a mile in height. Hence, with such a medium, we cannot conceive of some of the grand phenomena with which we are familiar having any existence in the lunar world—such as the noise of many waters and F of mighty thunderings-the voice of the passionate storm, or the melancholy wailing of the autumnal gales. No clouds are there, analogous to those which in ten thousand fantastic shapes are present with us, dropping fatness upon the fields, and casting shadows upon the landscape-a covert in the daytime from the heat. No rain, hail, or snow descends upon the lunar soil. It is difficult to imagine water at all, or any liquid, upon the surface; for if the atmospheric pressure were removed in relation to the earth, its liquids would be dissipated by the heat of the sun; and how much more might this result be expected at the surface of the moon, where the heat accumulated by its fifteen days' continuous exposure to the solar rays must be intense? There can be, therefore, no seas or lakes, or else evaporation would take place, and clouds be formed, perceptible through a telescope. But though apart from the majestic features of the ocean, the tracts of cloud that float in our atmosphere, and the commotions that agitate it, the lunar surface exhibits several points of accordance with the terrestrial superficies. There are mountains answering in their contour to those which diversify our own globe, intermingled with plains, glens, and extensive depressions. To the naked eye, the face of the moon appears chequered, exhibiting dusky patches and bright parts, which, in former times, the fancies of men converted into images of terrestrial things. Thus, Agesianax, as reported by Plutarch, supposed the moon's disk to reflect back to us, as in a mirror, the forms and outlines of our continents, islands, and seas. Nor is the idea so fanciful as not to have occurred to more than one mind. Observers have been impressed with it under widely different circumstances. It has continued to be a popular belief in Western Asia to the present day. Humboldt remarks: "I was once very much astonished to hear a very accomplished Persian of Ispahan, who had certainly never read a Greek book, to whom I was showing, in Paris, the spots on the moon's face through a large telescope, propound the same hypothesis of reflection as that of Agesianax as prevalent in his own country. It is ourselves we see in the moon,' said the Persian; 'that is the map of our earth.'' With the aid of a telescope, the lunar superficies presents an aspect that is excessively torn, ragged, and disturbed; and we are able to define peculiar physical features. There is, however, no foundation for some reports respecting the probable discovery of minute lunar objects; and but little reason to suppose that any instrumental power will be obtained sufficient to disclose them. Schroeter conjectured the existence of a great city on the east side of the orb, north of her equator, an extensive canal in another place, and fields of vegetation in another. Fraunhofer also announced the discovery of an edifice, resembling a fortification, together with several lines of road. The hope has likewise been entertained of discerning the dwellings and persons of the lunarians, should there be any; but these are visions, sanguine and baseless. Assuming, says M. Mädler of Berlin, that a German mile is the utmost limit of distance at which the keenest unassisted eye can distinguish human beings, to bring the moon to that distance, a magnifying power of 51,000 would be necessary; but, up to the present time, 300 is the highest power which has been applied to that object with advantage. Alone therefore, upon this ground, those who indulge the imagination of studying any lunar samples of social and domestic economy, are clinging to a forlorn hope. The time when the moon's unevenness of surface may be most favourably seen, is when she is horned or gibbous. The boundary of the light and dark parts of the disk would obviously be an unindented line if the disk were perfectly plane, and had no surfaces higher than the rest. But look at the lunar crescent. The bounding line appears notched and broken, which is precisely the aspect which elevations and depressions will produce. Close by the edge of the illuminated portion, yet within the dark part, wholly surrounded with shade, there are small shining points, like islands of light in a sea of darkness. These are gradually joined to the luminous space, and become part and parcel of it, as the moon L SELENOGRAPHIC MAP OF THE WHOLE VISIBLE HEMISPHERE 31 In order to understand the phenomena exhibited by the Moon 40 M 10 OF THE OON. 60 Sinu MARE VAPORUS Pa Nebula ARE ORUM Pales Porterdings &Play 1 Muskelyne 25 Hausen 49 Le Monnier 27 Puard 51 Aratus II 25 Maver II 34 Putet 35 Tycho 82 Guerike 52 Romontanus 84 Bonpland 57 Campanus 73 Versted 82 Aristoteles 57 Palitzsch 49 Mairun 50 Sharp 51 Louville 52 Harding 53 Gerard 54 Plato 55 Maupertius 56 Condamine 57 Biandini 58 Bouguer 59 Harpalus 60 Venopides 61 Repsold 62 Fontenelle 63 Hornbow 64 Trinaus 65 Geestratus 66 Xenophanes 67 Anaximander 68 Bythagoras 69 Epigenes 70 Anaxavoras 71 Philolaus 72 Anaximenes 66 Byrgius 85 Abulfeda 88 Ansgarius 80 Bohnenberger 109 Taylor 81 Beaumoni 110 Delambre Ill Theon sen. 112 Hipparchus 113 Reaumur |
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