228 Proceedings of the Royal Irish Academy. 



number of circumstances (notably the breccia-Eke appearance of some 

 meteorites) whicli show conclusively that the meteorites have been 

 torn from rocks which were ali'eady nearly, if not quite, solid; and as 

 it seems in the highest degree improbable that rocks of this nature 

 should exist in the sun, we may conclude that the sun has not been 

 the source of the meteorites. 



Can the meteorites have come from the moon ? Owing to the 

 small mass of the moon, the explosive power requisite to carry a body 

 away from the moon may no doubt be comparatively small ; but can a 

 body which has been projected from a volcano in the moon tumble 

 upon the earth ? To simplify questions of this kind ive shall suppose 

 -various disturhiny influences absent. We shall suppose that the pro- 

 jectile is discharged from the moon with sufficient velocity to carry it 

 completely therefrom. We shall then omit all account of the dis- 

 turbing influence both of the sun and the moon on the projectile, and 

 we shall suppose that the projectile is really revolving round the 

 earth as a satellite. This projectile will fall upon the earth if its 

 distance fi-om the earth's surface when in perigree be less than the 

 radius of the earth (augmented perhaps by the thickness of the 

 earth's atmosphere). It should, however, be observed, that if the 

 projectile once escaped the earth, it loould never fall thereon; hence the 

 question as to whether the moon can be the source of the meteorites 

 now falling appears to be connected with the question as to whether 

 the lunar volcanoes are now active. But it is generally believed that 

 the lunar volcanoes are not now active to any appreciable extent 

 (even if the suspected indications of recent change were thoroughly 

 established). It foUows, that even if the moon has been a source of 

 meteorites in ancient times, we no longer receive a supply from that 

 quarter. There is, of course, just a possibility that projectiles from 

 the moon in past ages, which have hitherto escaped collision with the 

 earth, may, under the influence of the disturhiny causes previoxi^shj 

 excepted, occasionally fall to the earth as a meteorite. 



Passing fi'om the sun and the moon, let us now bring under 

 review some of the other celestial bodies, and see how far they will 

 fulfil the conditions of the question, Is it possible that the meteorites 

 can have been projected from the surface of a planet ? In order to 

 get over the difficulties of the great initial velocity which would be 

 necessary to overcome the gravitation of a large planet, it seems 

 natural to inquire if a volcano placed upon one of the small planets 

 could accomplish the task. 



It is clearly impossible that a projectile from any soui'ce should 

 ever fall on the earth, unless the orbit of the projectile cuts the plane 

 of the ecliptic in the narrow ring, something over 8000 miles wide, 

 which the earth and its atmosphere trace out on the ecliptic ; but if a 

 meteorite with an elliptic orbit round the sun intersect this ring, then 

 in the lapse of time it may happen that the earth and the meteorite 

 will meet at the point where their orbits intersect ; the meteorite will 

 then fall upon the earth, and its long travels will be at an end. 



