quid becomes continuous.
Thus there will result a molten shell containing a gaseous nucleus
equally dense with itself at their surface of contact and more dense at
the centre--a molten shell which will slowly thicken by additions to
both exterior and interior.

That a solid crust will eventually form on this molten shell may be
reasonably concluded. To the demurrer that solidification cannot
commence at the surface, because the solids formed would sink, there are
two replies. The first is that various metals expand while solidifying,
and therefore would float. The second is that since the envelope of the
supposed spheroid would consist of the gases and non-metallic elements,
compounds of these with the metals and with one another would
continually accumulate on the molten shell; and the crust, consisting of
oxides, chlorides, sulphurets, and the rest, having much less specific
gravity than the molten shell, would be readily supported by it.

Clearly a planet thus constituted would be in an unstable state. Always
it would remain liable to a catastrophe resulting from change in its
gaseous nucleus. If, under some condition of pressure and temperature
eventually reached, the components of this suddenly entered into one of
those proto-chemical combinations forming a new element, there might
result an explosion capable of shattering the entire planet, and
propelling its fragments in all directions with high velocities. If the
hypothetical planet between Jupiter and Mars was intermediate in size as
in position, it would apparently fulfil the conditions under which such
a catastrophe might occur.

NOTE IV. The argument set forth in the foregoing note, is in part
designed to introduce a question which seems to require
re-consideration--the origin of the minor planets or planetoids. The
hypothesis of Olbers, as propounded by him, implied that the disruption
of the assumed planet between Mars and Jupiter had taken place at no
very remote period in the past; and this implication was shown to be
inadmissible by the discovery that there exists no such point of
intersection of the orbits of the planetoids as the hypothesis requires.
The inquiry whether, in the past, there was any nearer approach to a
point of intersection than at present, having resulted in a negative, it
is held that the hypothesis must be abandoned. It is, however, admitted
that the mutual perturbations of the planetoids themselves would
suffice, in the course