August 17,1372.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
125 
new fused material to form the cloud of, so to say, sili- 
cio us spray that lingers along and around the path of 
the meteoi’ite. 
When the mass is small,—and in the case of meteoric 
showers and ordinary falling stars it cannot exceed a 
few ounces, and may often he hut a few grains,—the 
whole material is thus consumed, and must ultimately 
fall as an unperceived, because widely-scattered, dust. 
The meteorite is the residue that survives this wasting 
action where the magnitude of the mass is more con¬ 
siderable. The cause of the violent and often successive 
explosions is probably to be sought in the expansion of 
the outer portions of the mass, while the interior retains 
the contracted volume due to the intense cold of space 
with which the meteorite enters the atmosphere. 
From time to time these contending conditions of 
volume may, as in a Prince Rupert’s drop, produce ex¬ 
plosion, the heated shell in the case of the meteorite 
tlying off in fragments from the internally cold inner 
core, which, if sufficient velocity remain to the mass, 
will undergo a recurrence of the same conditions of sur¬ 
face fusion and explosion. The loudness of the detona¬ 
tion is also probably enhanced by the simultaneous col¬ 
lapse of the air on the vacuum that would follow the 
rapidly moving mass. 
The pitted surface characteristic of meteorites pro¬ 
bably bears witness to a similar effect of unequal dila¬ 
tation operating more especially in the freshly-broken 
surfaces of the mass, small fragments splintering off in 
this way from the cold and brittle stone under the sud¬ 
den influence of intense heat. 
_ A remark made by Humboldt, that light and meteo¬ 
rites are the only sources of our knowledge regarding 
the universe external to our world, points to the true 
ground for our interest in the waifs and strays of extra- 
telluric matter that thus fall upon our globe. 
In physical as well as in chemical characters aero¬ 
lites resemble at the first aspect some terrestrial volcanic 
rocks. 
The minerals of which they are composed are nearly 
entirely crystalline, as is evidenced by the colours in 
polarized light of such as are transparent. These mine¬ 
rals are usually aggregated with slight cohesion, and 
they present in by far the greatest number of cases a 
peculiar spherular or u chondritic ” structure. 
In these the spherules are composed of similar mine¬ 
rals to those which enclose them, and even contain 
metallic iron sometimes in microscopically fine grains 
disseminated through them. 
A section of an aerolite was exhibited by the micro¬ 
scope in which some of the spherules had been broken 
before being cemented by the surrounding mass, and in 
another fissures were seen which had been filled with 
a fused material after one side of the fissure had slidden 
along the other; facts pointing to events in the history 
of the meteorite subsequent to its first formation. 
The chemical composition and the mineral constitu¬ 
tion of aerolites were illustrated by tables showing the 
elements met with in these bodies, and the minerals 
in which they were distributed. The former comprised 
about one-third of the known elements; among them 
magnesium, iron, silicon, oxygen, and sulphur were 
conspicuous; calcium, aluminium, nickel, carbon, and 
phosphorus coming next in importance, the basic ele¬ 
ments of most importance by their amount being the 
same as those which are found by spectroscopic analysis 
is to be present in the sun—and in those stars which 
have been the best examined. 
The minerals most frequent in aerolites besides nicke- 
liferous iron or troilite (iron monosulphide) and graphite, 
are bronzite (a ferriferous enstatite) and olivine, both the 
latter being essentially magnesium silicates. Augite 
and anorthite also occur (more particularly in the euk- 
ritic aerolites of Rose) and some minerals unknown in 
terrestrial mineralogy have also been met with; such 
are the different varieties of Schreibersitc (phosphides of 
iron and nickel) : calcium sulphide, asmanite (a form of 
silica crystallizing in the orthorhombic system and hav¬ 
ing the specific gravity of fused quartz), and a cubic 
mineral with the composition of labradorite. The crys¬ 
talline form of bronzite was first determined from the 
crystals in a meteorite, and was found to confirm the 
conclusion Descloizeaux had arrived at as regards its 
system from observations on the distribution of the optic 
axes in the terrestrial bronzite and enstatite. 
The question as to whence the meteorites come is one 
that we are not yet in a position to answer with cer¬ 
tainty. The various hypotheses which suppose for them 
an origin in lunar volcanoes, or in our atmosphere, or 
again in a destroyed telluric satellite, or that would treat 
them as fragments of an original planet of which the 
asteroids are parts, or as masses ejected from the sun ; 
all these hypotheses seem to be more or less precluded 
by the known velocities, the retrograde motion so fre¬ 
quently characterizing meteors and meteorites, or else 
by the chemical conditions that, for instance, arc involved 
in the passage of the meteorite through the sun’s chro 
mosphere. Whether meteorites move or do not move in 
circumsolar orbits is at present impossible to say; be¬ 
cause, while with our incomplete knowledge we cannot 
to-day attach the character of periodicity to any known 
class of meteorites, we are not justified in founding any 
conclusion on a negative result with so limited a founda¬ 
tion. 
But even if all or some of them may have been, on their 
encountering the earth, members temporarily or perma¬ 
nently of the solar system, we may with considerable 
probability consider them as having originally entered 
our system from the interstellar spaces beyond it. Such 
at least must be our conclusion if we are to admit the 
unity of the whole class of phenomena of meteorites and 
falling stars. For, since the orbits of the two best-known 
meteoric streams, those namely of August and Novem¬ 
ber, have been identified with the orbits of two comets, 
and since in regard to one of these (that of November) 
Levender has shown, with great probability, that as a 
meteoric cloud it entered and became a member of our 
system only some 1700 years ago in consequence of the 
attraction of Uranus, while the August meteoric ring- 
only differs in this respect from it, that it had at a much 
more remote period found an elliptic orbit round the sun ; 
we are constrained on the assumption with which we 
started to recognize also in a meteorite a visitor from the 
regions of remote space. And so far as it goes, the ob- 
j servation by Secclii that the November falling stars ex¬ 
hibit the magnesium lines is in harmony with this 
view. 
It may, however, further bo said, that the tendency of 
scientific conviction is in the direction of recognizing the 
collection towards and concentration in definite centres, 
of the matter of the Universe, as a cosmical law, rather 
than the opposite supposition of such centres being the 
| sources whence matter is dispersed into space. In the 
meteorites that fall on oar earth (certainly in consider¬ 
able numbers) we have to acknowledge the evidence of a 
vast and perpetual movement of matter in space, about 
which we can only reason as part of a great feature in 
the Universe which we have every ground for not sup- 
posing to be confined within the limits of the solar 
! system. 
That this matter, whether intercepted or not by the 
planets and the sun, should to an ever-increasing amount 
become entangled in the web of solar and planetary at- 
! traction, and that the same operation should be collect¬ 
ing round other stars and in distant systems such moving 
“ clouds” of star dust as have been treated by Schiaparelli, 
Leverrier, and other astronomers, or individual masses 
of wandering stone or iron is a necessary deduction from 
the view that we have assumed regarding the tendency oi 
cosmical matter to collect towards centres. Butin order to 
trace the previous stages of the history of any meteorite, 
and, in particular, to determine the conditions under 
