Sept. 30, 1886 | 
NATURE 535 
Besides this, they must have passed without destruction through 
an atmosphere of immense thickness. Then there is a geometric 
difficulty. The meteorite shot out from the sun would travel, 
under the law of gravitation, nearly in a straight line out and 
back again into the sun. If in its course it enters the earth’s 
atmosphere, its relative motion—that which we see—should be 
in a line parallel to the ecliptic, except as slightly modified by 
the earth’s attraction, A large number of these meteors, that 
is, most if not all well-observed fire-balls, have certainly not 
travelled in such paths. These did not come from the sun. 
It has been a favourite hypothesis that the meteorites came 
from some planet broken in pieces by an internal catastrophe. 
There is much which mineralogists can say in favour of such a 
view. The studies of M. Stanislas Meunier and others into the 
structure of meteorites have brought out many facts which make 
this hypothesis plausible. It requires, however, that the stone- 
meteor be not regarded as of the same nature as the star-shower 
meteor, for no one now seriously claims that the comets are 
fragments of a broken planet. The hypothesis of the existence 
of such a planet is itself arbitrary ; and it is not easy to under- 
stand how any mass that has become collected by the action of 
gravity and of other known forces should, by internal forces, be 
broken in pieces, and these pieces sent asunder. The disruption 
of such a planet by internal forces, after it has by cooling lost 
largely its original energy, would be specially difficult to 
explain. 
We cannot, then, look to the moon, nor to the earth, nor to 
the sun, nor to any of the large planets, nor to a broken planet, 
as the first home of the meteoroids, without seeing serious if not 
insuperable objections. But since some of them were in time 
past certainly connected with comets, and since we can draw no 
line separating shooting-stars from stone-meteors, it is most 
natural to assume that all of them are of a cometary origin. Are 
there any insuperable objections that have been urged against 
the hypothesis that all of the meteoroids are of like nature with 
the comets, that they are in fact fragments of comets, or it may 
be sometimes minute comets themselves? If such objections 
exist, they ought evidently to come mainly fron the mine- 
ralogists, and from what they find in the internal structure of 
the meteorites. Astronomy has not as yet furnished any objec- 
tions. It seems strange that comets break in pieces, but astro- 
nomers admit it, for it is an observed fact. It is strange that 
groups of these small bodies should run before and follow after 
comets along their paths, but astronomers admit it as fact in the 
case of at least four comets. Astronomically there would seem 
to be no more difficulty in giving such origin to the sporadic 
meteor, and to the large fire-ball, and to the stone-meteor, than 
there is in giving it to the meteor of the star-shower. If, then, 
the cometic origin of meteorites is inadmissible, the objections 
must come mainly from the nature and structure of the meteoric 
stones andirons. Can the comet in its life and history furnish 
the varied conditions and forces necessary to the manufacture or 
growth of these peculiar structures ? 
It is not necessary, in order to answer this question, to solve 
the thousand puzzling problems that can be raised about the 
origin and the behaviour of comets. Comets exist in our system, 
and have their own peculiar development, whatever be our 
theories about them. It will be enough for my present purpose 
to assume as probably true the usual hypothesis that they were 
first condensed from nebulous matter; that that matter may 
have been either the outer portions of the original solar nebula, 
or matter entirely independent of our system and scattered 
through space. In either case, the comet is generally supposed, 
and probably must be supposed, to have become aggregated far 
away from the sun. ‘This aggregation was not into one large 
body, to be afterwards broken up by disruption or by solar 
action. The varieties of location of the cometic orbits seem 
inexplicable upon any such hypothesis. Separate centres of 
condensation are to be supposed, but they are not @ f7zo7v¢ un- 
reasonable. This is the rule rather than the exception every- 
where in Nature. 
Assume, then, such a separate original condensation of the 
comet in the cold of space, and that the comet had a very small 
mass compared with the mass of the planets. Add to this the 
comet’s subsequent known history, as we are seeing it in the 
heavens. Have we therein known forces and changes and con- 
ditions of such intensity and variety as the internal structure of 
the meteorites calls for? What that structure is, and, to some 
extent, what conditions must have existed at the time and place 
of its first formation, and during its subsequent trausfo-mations, 
mineralogists rather than astronomers must tell us. For a long 
time it was accepted without hesitation that these bodies re- 
quired great heat for their first consolidation. Their resem- 
blance to the earth’s volcanic rocks was insisted on by mineralo- 
gists. Prof. J. Lawrence Smith, in 1855, asserted without 
reserve that ‘‘they have all been subject to a more or less pro- 
longed igneous action corresponding to that of terrestrial 
volcanoes.” Director Haidinger, in 1861, said, ‘‘ With our 
present knowledge of natural laws, these characteristically crystal- 
line formations could not possibly have come into existence except 
under the action of high temperature combined with powerful 
pressure.” The likeness of these stones to the deeper igneous 
rocks of the earth, as shown by the experiments of M. Daubrée, 
strengthened this conviction. Mr. Sorby. in 1877, said, ‘‘It 
appears to me that the conditions under which meteorites were 
formed must bave been such that the temperature was high 
enough to fuse stony masses into glass ; that the particles could 
exist independently one of the other in an incandescent atmo- 
sphere subject to violent mechanical disturbances ; that the force 
of gravitation was great enough to collect the-e fine particles 
together into solid masses, and that these were in such a situation 
that they could be metamorphosed, further broken up into 
fragments, and again collected together.” 
Now, if meteorites could come into being only in a heated 
place, then the body in which they were formed ought, it would 
seem, to have been a large one. But the comets, on the con- 
trary, appear to have become aggregated in small masses. The 
idea that heat was essential to the production of these minerals 
was at first anatural one. All other known rock-formations are 
the result of processes that involve water or fire or metamorph- 
ism. All agree that the meteorites could not have been formed 
in the presence of water or free oxygen. What conclusion was 
more reasonable than that heat was present in the form of yol- 
canic or of metamorphic action ? 
The more recent investigations of the meteorites and kindred 
stones, especially the discussions of the Greenland native irons 
and the rocks in which they were embedded, are leading 
mineralogists, if I am not mistaken, to modify their views. 
Great heat at the first consolidation of the meteoric matter is 
not considered so essential. In a late paper M. Daubrée says :— 
“Tt is extremely remarkable that, in spite of their great tend- 
ency to a perfectly distinct crystallisation, the silicate combina- 
tions which make up the meteorites are there only in the con- 
dition of very small crystals, all jumbled together as if they had 
not passed through fusion. If we may look about us for some- 
thing analogous, we should say that, instead of calling to mind 
the long needles of ice which liquid water forms as it freezes, 
the fine-grained texture of meteorites resembles rather that of 
hoar-frost, and that of snow, which is due, as is known, to the 
immediate passage of ‘the atmospheric vapour of water into the 
solid state.” So Dr. Reusch, from the examination of the 
Scandinavian meteorites, concludes that ‘‘there is no need to 
assume volcanic and other processes taking place upon a large 
heavenly body formerly existing, but which has since gone to 
pieces.” 
The meteorites resemble the lavas and slags on the earth. 
These are formed in the absence of water, and with a limited 
supply of oxygen, and heat is present in the process. But is 
heat necessary? Some crystallisations do take place in the cold ; 
some are direct changes from gaseous to solid forms. We can- 
not in the laboratory reproduce all the conditions of crystallisa- 
tion in the cold of space. We cannot easily determine whether 
the mere absence of oxygen will not a:count fully for the slag- 
like character of the meteorite minerals. Wherever crystallisa~ 
tion can take place at all, if there is present silicon and magne- 
sium and iron and nickel, with a limited supply of oxygen, 
there silicates ought to be expected in abundance, and the iron 
and nickel in their metallic form. Except for the heat, the pro- 
cess should be analogous to that of the reduction of iron in the 
Bessemer cupola, where the limited supply of oxygen combines 
with the carbon and leaves the iron free. The smallness 
of the comets, should not, then, be an objection to considering 
the meteoric stones and irons as pieces of comets. ‘There is no 
necessity of assuming that they were parts of a large mass, in 
order to provide an intensely heated birth-place. 
But although great heat was not needed at the first formation, 
there are many facts about these stones which imply that violent 
forces have in some way acted during the meteorites’ history. 
The brecciated appearance of many specimens, the fact that the 
fragments in a breccia are themselves a finer breccia, the frac- 
