1888.] Conditions of a Swarm of Meteorites, <$-c. 5 



mechanics of a swarm of meteorites, with special numerical applica- 

 tion to the solar system. 



When two meteoric stones meet with planetary velocity, the stress 

 between them daring impact must generally be such that the limits 

 of true elasticity are exceeded, and it may be urged that a kinetic 

 theory is inapplicable unless the colliding particles are highly elastic. 

 It may, however, 1 think, be shown that the very greatness of the 

 velocities will impart what virtually amounts to an elasticity of a high 

 order of perfection. 



It appears, a priori, probable that when two meteorites clash, a 

 portion of the solid matter of each is volatilised, and Mr. Lockyer 

 considers the spectroscopic evidence conclusive that it is so. There 

 is no doubt enough energy liberated on impact to volatilise the whole 

 of both bodies, but only a small portion of each stone will undergo 

 this change. A numerical example is given in the paper to show the 

 enormous amount of energy with which we are dealing. It must 

 necessarily be obscure as to how a small mass of solid matter can take 

 up a very large amount of energy in a small fraction of a second, bat 

 spectroscopic evidence seems to show that it does so ; and if so, we 

 have what is virtually a violent explosive introduced between the two 

 stones. 



In a direct collision each stone is probably shattered into frag- 

 ments, like the splashes of lead when a bullet hits an iron target. 

 But direct collision must be a comparatively rare event. In glancing 

 collisions the velocity of neither body is wholly arrested, the con- 

 centration of energy is not so enormous (although probably still 

 sufficient to effect volatilisation), and since the stones rub past one 

 another, more time is allowed for the matter round the point of 

 contact to take up the energy ; thus the whole process of collision is 

 much more intelligible. The nearest terrestrial analogy is when a 

 cannon-ball rebounds from the sea. In glancing collisions fracture 

 will probably not be very frequent. 



From these arguments it is probable that, when two meteorites 

 meet, they attain an effective elasticity of a high order of perfection ; 

 but there is of course some loss of energy at each collision. 



[It must, however, be admitted that on collision the deflection of 

 path is rarely a very large angle ; but a succession of glancing colli- 

 sions would be capable of reversing the path, and thus the kinetic 

 theory of meteorites may be taken as not differing materially from, 

 that of gases.*] 



Perhaps the most serious difficulty in the whole theory arises from 



the fractures which must often occur. If they happen with great 



frequency, it would seem as if the whole swarm of meteorites would 



degrade into dust. We know, however, that meteorites of consider- 



* Added on November 16, 1888. 



