230 Proceedings of the Royal Irish Academy. 



It is thus evident that there are two objections to Ceres (and the 

 same may be said of the other minor planets) as a possible source of 

 the meteorites. Firstly, that not-withstanding the small mass of 

 Ceres, a veiy powerfal volcano T\'ould be required; and secondly, that 

 we are obliged to assume that for each meteorite which could ever fall 

 upon the earth, at least 50,000 must have been ejected. 



It thus appears that if the meteorites have been originally driven 

 from any planet of the solar system, large or small, the volcano must, 

 from one cause or another, be a very poweiiul one. 



There is, however, one planet of the solar system which has a 

 special claim to consideration. On that planet it is true that a vol- 

 cano would be required which was capable of giving an initial velocity 

 of at least six miles per second ; but every projectile launched fi'om 

 that volcano into space would, after accomplishing an elliptic orbit 

 round the sun, dash through the track of the earth, and again pass 

 through the same point at every subsequent revolution. It is not 

 here a case of one solitary projectile out of 50,000 crossing the earth's 

 track, but every one of the 50,000 possesses the same property. The 

 planet of which we are speaking is, of course, the earth itself. If in 

 ancient times there were colossal volcanoes on the surface of the earth 

 which had sufficient explosive energy to drive missiles upwards with 

 a velocity sufficient to cany them away from the earth's surface, after 

 making allowance for the resistance of the air, these missiles would 

 then continue to move in orhits roiincl the sun, crossing at each revolu- 

 tion the point of the earth's track from which they were originally 

 discharged. If this were the case, then doubtless there are now 

 myriads of these projectiles moving through the solar system, the 

 only common feature of their orbits being that they all intersect the 

 earth's track. It will, of course, now and then happen that the earth 

 and the projectile meet at the point of crossing, and then we have the 

 phenomenon of the descent of a meteorite. The theoiy, that the 

 meteorites have originated in the earth, was, so far as I know, first put 

 forward by Dr. Phipson. ILr. J. Lawrence Smith, in a letter I re- 

 ceived from him some months ago, inclines to the same view as at aL 

 events one of the probable sources. 



It is well to note here the great diffierence between the lunai 

 theoiy of meteorites and the terrestrial theory. Por the lunar theory 

 to be true it would probably be necessary that the lunar volcanoes 

 should be still active. In the terrestrial theory it is only necessary to 

 suppose that the volcanoes on the earth once possessed sufficient ex- 

 plosive energy. No one supposes that the volcanoes on the earth at 

 present eject the fragments which will constitute future meteorites, 

 but it seems probable that the earth may be now slowly gathering 

 back in these quiet times the fi'agments she ejected in an early stage 

 of her history. 



Assuming, therefore, that the meteorites have had a quasi-\ olc^mo, 

 origin on some considerable celestial body, I am led to agree with 

 those who believe that most probably that body is the earth. 



