A SWAEM OF METEORITES, ARC ON THEORIES OF COSMOGONY. 
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there is, however, no analysis in §§ 1 and 2. The reader who only wishes to know 
the arguments and results, without a consideration of the mathematical details, is 
therefore recommended, after reading §§ 1 and 2, to pass on to the Summary. 
§ 1. On the Effective Elasticity of Meteorites in Collision. 
When two meteoric stones meet with planetary velocity, the stress between them 
during 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, I 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 joriori, 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 rough numerical example will show the kind of f[uantities with which we are 
here dealing. 
It will appear hereafter that the mean velocity of a meteorite may be at the least 
about 5 kilometres a second; and, accordingly, the mean relative velocity of a pair 
would then be about 7 kilometres a second."^ Hence, if two stones, weighing a 
kilogramme, move each with a velocity of 3^ kilometres per second directly towards 
one another, the energy liberated at the moment of impact is 2 X X 10'^ (3-^ X 10'^)“ 
or 12 X 10^® ergs. 
Now Joule’s ecpiivalent is 4'2 X 10'^ ergs; hence, the energy liberated is about 
3 million calories. 
It is quite uncertain how much of each stone would be volatilised ; but, if it were 
3 grammes, there would be a million calories of energy applied to each gramme. 
The melting temperature of iron is about 1500 degrees Centigrade, and the mean 
specific heat of iron may be about y.t Hence, about 300 calories are required to raise 
a gramme of iron from absolute zero to melting point. I do not know the latent heat 
of the melting of iron, but for platinum it is 27, and the latent heat of volatilisation 
of mercury is 62. Hence, about 400 or 500 calories suffice to raise a gramme of iron 
from absolute zero to volatilisation. It is clear, then, that there is energy enough, 
not only to volatilise the iron, but also to render the gas incandescent; and the same 
would be true if the mass operated on by the energy were 30 grammes instead of 3. 
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, but 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. 
* If V be the velocity of mean square, \/ 2 is the sqnare root of the mean square of relative velocity. 
t ‘ Physikaliscli-Cbemiscbe Tabellen.’ Landolt and Bornstein. 
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