METEORIC STONES AND SHOOTING STARS. 



435 



Until, therefore, the advocates of the planetary hypothesis can remove these 

 difficulties, that theory cannot be admitted. 



The lunar hypothesis appears to be compatible, generally, with the circum- 

 stances of aerolites. It explains satisfactorily enough the force and direction 

 of their collision with the earth. If it be admitted that they proceed from the 

 same lunar volcano, or that all lunar volcanoes eject the same kind of substan- 

 ces, the similarity of their constituents will be explained ; in short, all that is 

 > necessary to raise the lunar hypothesis to the rank of a theory is to prove the 

 fact that there really do exist volcanoes in the moon. Now although observa- 

 tion has supplied circumstances which give some probability to that idea, yet 

 it is still very far from being clearly established. Telescopic examination of 

 the lunar surface, has certainly and clearly established the fact that it is covered 

 in every part that is visible with mountains, having all the external forms and char- 

 acters of terrestrial volcanoes. The craters are not only distinctly visible, but 

 we have been enabled to ascertain the existence of the cones within them. 

 Sir John Herschel, who has had the advantage of observing with the most \ 

 powerful reflecting telescopes, has declared that the generality of the lunar 

 mountains present a striking uniformity and singularity of aspect. They are 

 wonderfully numerous, occupying by far the larger portion of the surface, and 

 almost universally of an exactly circular or cup-shaped form, foreshortened, 

 however, into ellipses toward the limb ; but the larger have 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 volcanic character, as it 

 may be seen in the crater of Vesuvius, and in a map of the volcanic districts 

 of the Campi Phlegraei or the Puy de Dome. And in some of the principal 

 ones, decisive marks of volcanic stratification, arising from successive depos- 

 ites of ejected matter, may be clearly traced with powerful telescopes. What 

 is, moreover, extremely 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 ceas, when closely examined, present appearances incom- 

 patible with the supposition of deep water), yet there are large regions per- 

 fectly level, and apparently of a decidedly alluvial character. 



But this condition of things may have resulted from volcanic action, which 

 took place at an epoch long antecedent to the commencement of the present 

 condition of our globe, and it may be required to establish the fact of the pres- 

 ent existence of active volcanoes on the moon. 



To this it may be answered, first, that if active volcanoes existed at any re- 

 mote period, the substances ejected from them may have been ever since re- 

 volving in the space around the earth, and that they may now, from time to 

 time, become entangled in the earth's atmosphere and descend to the surface. 



Secondly, it may be replied that we do possess indications of the present 

 existence of lunar volcanoes, inasmuch as bright, luminous spots have been 

 detected by various astronomers at different times and places, on the occasion 

 of total eclipses of the sun, on the surface of the moon, then dark, and that it is 

 impossible, on the one hand, to deny the existence of what has been witnessed 

 by so many competent observers, and that no other supposition has been offer- 

 ed to explain such luminous spots, except one, which from its extreme improb- 

 ability cannot be seriously entertained, namely, that which supposes the sun 

 to have been rendered visible by holes through the moon. 



Thus, then, stands the lunar theory of meteorites. It is exempt from most 

 of the difficulties and objections that attend the other hypotheses, but neverthe- 

 less, until it be actually established beyond all question that there are, or have 

 been, active volcanoes on the moon, and that substances ejected from these 

 have actually fallen upon the earth, the luna^theory of meteorites cannot be 



