218 ASTRONOMY. 



1879 — one by Dr. Ball, the astronomer royal for Ireland, and the other 

 byM. Stanislas Meiinier, of whom a commission of the Paris Academy 

 said that he was justified in concluding "that all these masses once be- 

 longed to a considerable globe like the earth, having true geological 

 epochs, and that later it was decomposed into separate fragments under 

 the action of causes difficult to define exactly, but which we have more 

 than once seen in operation in the heavens themselves." Dr. Ball's the- 

 ory is founded on the arguments which induced Tschermak to believe 

 that he had proved meteorites to have no connection with shooting-stars, 

 but to have their origin in volcanic eruptions in other planets so small 

 that projectiles from them would not be driven back by the force of 

 gravity. On the smallness of such planets Dr. Ball lays no stress, and 

 indeed he first considered whether or not our meteorites may not come 

 from the sun, rejecting this theory, however, on the ground that such 

 solid rock masses as occasionally fiUl could hardly exist in such a bod^' 

 as the central source of heat. The sun failing, Dr. Ball turns to the 

 moon, which also he rejects as a possible source, since, although it once 

 might have thrown out meteoric masses, they would either fall at once 

 to the earth or back upon the moon, or missing the earth would continues 

 to travel round it, and probably in the course of centuries return to their 

 original source. We must then assume that in her present cold state 

 our satellite is continually throwing out bodies from active volcanoes — 

 a supposition which no selenographer will entertain for a moment. For 

 very good physical reasons Dr. Ball rej'ects also the different planets as 

 sources of aerolites, and 'holds that they have had their origin on the 

 earth itself, which, though in its present geological state it has no power 

 to expel bodies with so great a velocity as his theory requires, yet was 

 certainly once possessed of volcanoes which might have performed the 

 work of throwing out matter with velocity enough to carry them beyond 

 terrestrial influence and send them in orbits of their own around the 

 sun, crossing at each revolution the point at which they were shot from 

 the earth's orbit. If this be true, showers of meteors should occur when- 

 ever the earth chanced to reach a point where a meteoric track crossed 

 hers, and the aerolites would come back to their source. 



At about the same time when Dr. Ball was elaborating this theory 

 astronomers were following the researches of Daubr^e, which seemed to 

 indicate a likeness in jjhysical characteristics between meteorites and 

 the lower rock strata of the earth. M. Meunier, Avho was a pupil of 

 Daubree, found that this analogy had not to do alone with mineralogi- 

 cal constitution, but " extended to the relation which these cosmical 

 materials disseminated in space present when compared among them- 

 selves as we compare the constituent rocks of our globe." His conclu- 

 sion, as given above, was that the meteorites, therefore, came from a 

 ''considerable globe like the earth," having geological epochs analogous 

 to ours, but now broken up and disseminated through space, as at some 

 time our own globe may be. Xotwithstanding the way in which this 



