TRANSACTIONS OF THE SECTIONS. 189 
the only satisfactory solution seems to be that recognized by most physicists, namely, 
that it is the result of the heat generated by the aérolite entering the earth’s 
atmosphere with the velocity of a cosmical body, and of that velocity being 
reduced with a suddenness that brings down the motion of the aérolite to that of 
a falling body in a few seconds of time. The light associated with the fall of such 
a body is probably due in part, as Haidinger has suggested, to the actual incandes- 
cence of the air, partly to the combustion of the iron and the ignition of the stony 
material as the surface of the aérolite fuses and streams away in a state of ignition 
and is thus left behind it in its path. The reports heard may be due to the actual 
bursting of the mass into fragments, from the gradual penetration towards the 
interior of the high temperature constantly being developed on its surface. That 
interior, bringing with it the intense cold of space, and the contracted volume due 
to that coldness (probably also brittle in consequence of it), remains in its more 
shrunk state, while the outer parts are expanding. Wherever there are lines of 
weaker ageregation therefore in the mass, or where the heat is able, from differences 
of conducting power in the material, to penetrate the mass unequally, a tendency 
in parts of the mass to break away from an inner core will ensue, and the explosion 
is the result. The causes that have combined to sever the mass into fragments 
may recur to cause explosions in the fragments, especially if their coherence has 
been shaken and cracks have been formed in them. If the aérolite has not lost too 
much of its velocity at the time of the explosions, the incrustation will reeommence 
on the fresh surfaces. Where the velocity has been too far reduced, this process 
will not be repeated, and the stones will fall without a crust on the faces of fracture. 
~ Intermediate stages of slight incrustation and even of a mere thin glazing are by 
no means rare, and several of these are illustrated by specimens in the British 
Museum. 
Mr. Maskelyne next pointed out the conditions which must have been present 
in the earlier stages of the history of an aérolite. The presence of an excess of iron 
and a deficiency of oxygen is attested by the existence of metallic iron in almost 
every known aérolite. One has to imagine a mixture of molten metals gradually 
oxidizing in a rare atmosphere, and to suppose that the more oxidizable of them 
take precedence in their claim to the oxygen. These have, probably, during the 
process displaced some of the iron and nickel where these metals had become 
already combined, as in the cases where we find the iron isolated in the form of a 
microscopic, often crystallized dust in the interior of aérolitic minerals (like the 
suboxide of copper in avanturine glass). We have also evidence of stages in the 
history of the formation of an aérolite. The orbicular structure of so many of 
these bodies is an indication of one stage of this kind. The spherules which cha- 
racterize this structure are often composed of a single crystalline and homogeneous 
mineral, with a radiating structure; often they are breccias made up of several 
erystals of the same or of different minerals united by a granular network of mineral, 
These spherules are often surrounded by a shell of meteoric pyrites or iron, and 
are set in a mixed mass, often highly porphyritic, composed of similar ingredients 
with the spherules. The solidification of this ground-mass marks, probably, a second 
stage in the history, the former indicating the very gradual separation by cooling 
of some of the ingredients of the aérolite, and the latter the result of the further 
gradual cooling of the residuary mass. There is no glass or uncrystallized matter 
apparent in any aérolite yet examined. Hence the meteorite, while presenting 
analogies with a slag in so far as that it is produced in the presence of an excess of 
metal, is in other respects analogous to a lava from the gradual manner in which 
its cooling has taken place and the different minerals have become separated out. 
A third stage in the history of the aérolite is exhibited in the veins of metallic 
iron and of other substances which are so often found not only cementing the sides 
of narrow fissures in meteorites, but frequently in the more compact varieties 
traversing with those fissures the substance of the spherules, and producing in them 
and the surrounding mass the phenomenon of “a heave,” such as one sees in a 
lode when the two sides of the fissures have shifted their relative positions. 
The next subject introduced was that of the minerals contained in a®rolites; and 
Mr. Maskelyne pointed out that, from the optical characters exhibited by these 
minerals when under microscopic examination, he was led to believe that augite 
