753 



AIOON. 



MOON. 



that the figure of a spot varies exceedingly according to the degree different periods of the lunation, and the alteration in some is so great 



illumination. Thus many spots and appearances that are that they are with difficulty recognised as the same spots. Many 



rongly marked iu the increasing or waning moon are almost if not , astronomers are consequently at the present time engaged in following 



entirely invisible at the time of full moon. They also vary greatly at I and delineating the appearance of certain spots through the whole 



l>eriod of a lunation, and thus it is hoped future observers may be 

 enabled to verify them at any time during that period. This if fully 

 carried out would be a most valuable boon to persons engaged in lunar 

 investigitio'H. ai every variation arising from the before-mentioned 

 causes would be re idily recognised ; and should any actual alteration 

 take place in any of these craters, a thing that has repeatedly been 

 .suspected, it could not fail hi being immediately detected. 



The names of the spots were first given by Hiccioli, and his nomen- 

 clature is still generally followed, although with very numerous 

 additions- Tbe spots are distinguished by the names of eminent 

 astronomers, philosophers, and mathematicians, both ancient and 

 modern, as Eratosthenes, Plato, Pythagoras, Archimedes, Tycho, Coper- 

 nicift, Kepler, &c. Many . of these spots deserve a more particular 

 notice. Thus Tycho, the large crater hi the centre of the lower |>art of 

 the cut, is remarkable, not only on account of its brilliancy and size, 

 (being 54 miles in diameter, and in depth 16,600 feet,) but also for the 

 radiating streaks, which proceed from it in all directions, some of 

 which extend into the opposite hemisphere. Copernicus, a con- 

 spicuous spot to the left of the cut. and about lialf way to the top, 

 presents an immense crater, 56 miles in diameter, in the centre of 

 which is a mountain having six peaks, of which two are very cou- 

 -ipiouom. It is surrounded by a ring composed of successive ten-aces, 

 ending in a narrow ridge, and rising to the height of 1 1 ,000 feet from 

 the bottom of the crater Aristarchm, the spot still m jre to the 

 left above Copernicus, is the brightest crater in the moon ; it is so 

 brilliant as to be quite dazzling in a large telescope. It is this spot that 

 was aupposed by dir William Herschel to be a volcano in eruption. 

 Plato, a Urge dark oval spot in the upper portion of the cut, is 



ARTS AXD SCI. DIV. VOL. V. 



remarkable for having the bottom of the crater striped, which is also 

 the case with Archimedes, a large oval spot at no great distance from 

 Plato, in which seven nearly parallel stripes may be easily distin- 

 guished. Near Plato is a remarkable insulated pyramidal mountain 

 or rock called Pico, rising from a narrow base to about 7000 feet above 

 the surrounding plain, from which it must present a most magnificent 

 appearance. Eratosthenes, a crater situated near a ridge of lofty 

 mountains called the Apennines, is also a very brilliant object, and 

 Stadius, a neighbouring crater, is one of those to be seen only under 

 peculiar illumination, being absolutely invisible at the time of full 

 moon. 



The surface of the moon exhibits a very large number of moun- 

 tains " almost universally of an exactly circular or cusp shaped form, 

 foreshortened however into ellipses near the limb ; but the larger havo 

 for the most part flat bottoms within, from which rises centrally a 

 small, steep, conical hill. They offer in short, in its highest perfection, 

 the true tuleanic character, as it may be seen in the crater of Vesuvius. 



And in some of the principal ones, decided marks of volcanic 



stratification, arising from successive deposits of ejected matter, may 

 be clearly traced with powerful telescopes. What is moreover ex- 

 tremely singular in the geology of the moon is, that although nothing 

 having the character of seas can be traced (for the dusky spots which 

 are commonly called seas, when closely examined, present appearances 

 incompatible with the suppoait on of deep water) yet there are large 

 regions perfectly level, and apparently of a decided alluvial character." 

 (Sir J. Herschel, ' Astronomy,' p. 229.) The mountains are known by 

 their shadows, which are perfectly visible, and which are long when 

 they arc near the boundary of light and darkness, or when the sun U 



