92 



Influence of Gravity on the 



Art. IX. — On the Influence of Gravity on the Physical 

 Condition of the Moon's Surface, 5y Balt'OUR Stewart, 

 Esq. 



The great irregularities of the surface of our satillite, are 

 discernible almost without the aid of a telescope, but, by 

 means of this instrument they have been accurately measured; 

 and their stupendous character impressed upon the mind, 

 which is thus enabled to compare them with the irregularities 

 of the Earth's surface. The appearance presented by the 

 moon's disc, is thus described by the Rev. Josiah Crampton, 

 in his work entitled The Lunar World ; its Scenery y 

 Motions, 



" Xot only," lie remarks, are her mountains more numerous in 

 proportion to her size than those of the eai'th, but they are much larger, 

 rising to a much loftier elevation, composed apparently of a substance 

 of a much harder texture than any thing terrestrial, and exhibiting 

 bolder and sharper outlines, and more tremendous precipices, some of 

 which project and overhang each other in such a manner as to lead 

 many to suppose that the rocks composing them are of a harder and 

 more solid nature than wrought iron." 



And the Dublin University Magazine, for February, 1854, 



remarks on the same subject. 



" Some important diversity must prevail, no doubt, for it cannot be 

 by chance, that in the lesser liody sheer cliffs of thousands of feet des- 

 cend from mountain tops into the valleys or chasms, while in the larger, 

 no search has yet succeeded in discovering a perpendicular descent of 

 five hundred feet anywhere. The moon's craters cling to the sides of 

 cliffs, cut into, encompass, and over-leap each other. In dimensions 

 some of them measure one hundred miles." 



With regard to the cause of this diversity I would venture 

 an explanation. I do not look for it in any difference of 

 material; for I am neither inclined to imagine with some that 

 the moon's surface has more tenacity than wrought iron, nor 

 with others that it resembles cork. I would rather look for 

 its chief cause in the difference between terrestrial and lunar 

 gravitation. A long rod of iron will bend, and a sufficiently 

 long rod of any brittle subvstance will break by its own 

 weight; but if these be placed, in circumstances where they 

 retain their tenacity and all their other qualities unchanged, 

 with the exception of their gravity, which is lessened, the 

 rod of iron will not bend so nmch, and it will require a greater 

 leno-th of the brittle substance in order to break it. Now 

 the^ weight of the same body is much less on the moon's 

 surface than on the eartli's. For the attraction of a sphere 

 of matter on any point, without its force and distance, is the 



