S88 Geology, of the Moon. 



full moon : he may witness it during tlio full, in all its brightness, and see 

 some traces of it five days afterwards, without being able to discover spots 

 of any other kind, for example annular mountains. But if he examine this 

 same region, when it is near the limit of the light, the state in which Cassini 

 found it in 1673, he will then very clearly distinguish mountains of this 

 kind, which will be new to him if he has examined the region only by a 

 more direct illumination. We can readily perceive to liow many errors of 

 a similar kind this change of aspect may lead ; and it is owing to analo- 

 gous optical illusions, proceeding from differences of illumination, or from 

 variations in our atmosphere, tliat Messrs Baer and Madler attribute, 

 among other causes, the physical changes which Schroeter has thought he 

 observed upon the surface of the moon. 



There is not a single one of the bands of Tycho which, according to our 

 observations, shews the least elevation of level which is properly its own. 

 It is thus that these bands present exactly tlie same intensity of light, whe- 

 ther in the plain of Stoefler, which is uniform like a mirror, or on the an- 

 nular mountain of the same name, which is 2000 toises in height. 



2. Geology of the Moon. — After having presented, in the foregoing quota- 

 tions, a specimen, as it were, of the lunar toxjography of Alessi-s Baer and 

 !RIadler, we may now mention the manner in which they endeavour to ac- 

 count, in accordance with the known laws of physics, for the appearances 

 which the surface of our satellite presents. However hypothetical these 

 ideas may be, yet they possess a true interest as proce?ding from observers 

 so accurate and judicious, and they are likely to suggest new researches. 

 They offer them with all possible and most commendable reserve. We take 

 them from the concluding part of their treatise. 



The authors adopt the idea of Count Laplace concerning the formation of 

 the celestial bodies of our system. They admit that the moon was origin- 

 ally in a state of heat and fluidity analogous to that in which every thing- 

 seems to prove that the earth has been. They even suppose that the moon 

 at first was in a gaseous state, and that it gradually passed into a solid con- 

 dition, like the other planets and satellites, by a gradual condensation and 

 cooling. This cooling, they remark, must necessarily have taken place 

 sooner in the external parts than in the internal, and consequently a crust 

 must have been formed Avlien the interior was yet in a state of gas. Those 

 portions of the mass which remained in this last condition in separating 

 themselves from the molecules which were condensed, not being able to 

 escape outwardly without opposition, violent ruptures and eruptions {a2tS' 

 ■briiche) were the consequerice. 



We cannot assign a value to the time during which these reactions 

 occurred, nor can we calculate their comparative force, or determine, n 

 priori, what must have been the result in each celestial body in particular. 

 The power of contraction in the several masses, the elasticity of the gases, 

 the relation of the spaces to the different epochs of formation, the tempera- 

 tures, and, finally, the weight, might and must present differences so great, 

 that one body might experience only a variety of fractures, another so many 

 elevations, and a third, over a certain extent, might experience neither the 

 one nor the other of these effects. At the same time it appears, that in a 



