A. MATHEMATICS AND ASTRONOMY. 25 



in this respect, like our moon. Astron. JVach., LXXXIIL, 

 276. 



THE MOON CONSIDERED AS A AVORLD. 



According to Mr. Nasmvth's recent work on the moon, the 

 geological influences that have been operating upon its sur- 

 face in past ages, to form the peculiar volcanic craters and 

 other phenomena observed by astronomers, are essentially of 

 the same nature as those that have also been operating upon 

 the earth's surface. The observations made by Mr. Nas- 

 myth during many years have enabled him to construct 

 models of certain portions of the lunar surface, which, when 

 placed with a strong light shining obliquely upon them, re- 

 produce the ever-changing effects of light and shadow ob- 

 served through the telescope. These models he has photo- 

 graphed, and thus produced the most perfect representations 

 of lunar scenery ever yet published. Besides the craters, 

 which are of such general interest, Messrs. Nasmyth and Car- 

 penter have given special attention to the bright streaks ra- 

 diating from certain regions of volcanic activity. More than 

 a hundred such bright streaks radiate from the great crater 

 Tycho, and these traverse plains, mountains, craters, and nil 

 asperities, holding their way totally regardless of every ob- 

 ject that happens to lie in their course. Quite different from 

 these " streaks " are the " cracks," some of which are easily 

 seen, but most of those recorded by Messrs. Nasmyth and 

 Carpenter are excessively delicate objects. The authors in- 

 cline to the belief that the moon never had an atmosphere, 

 properly so called, and maintain that the volcanic action of 

 the moon depended, not upon the agency of gases, vapors, 

 nor water, but upon a principle announced by them; namel} r , 

 that most solids expand as, in cooling, they pass from the 

 liquid to the solid form, and that this expansion of the mate- 

 rial, which, at one time, was in a molten condition, caused the 

 crust of the moon to occupy a larger volume than the orig- 

 inal molten mass. Unable, however, by its weakness, to pre- 

 serve itself intact, the crust cracked, and through these cracks 

 the interior liquid was ejected. This theory has some points 

 in common with that maintained by Mallet in explaining the 

 phenomena of vulcanicity on the earth's surface, but differs 

 essentially in that Mallet's theory requires the intervention 



B 



