he density of the entire planet thus formed equal
to that of Jupiter, or about one-third greater than the density of
water. In this argument there are in reality two assumptions, of
precisely the same nature as those which Whewell set himself to combat.
It is first assumed that some material existing on a large scale in our
earth, and nearly of the same density as Jupiter, must constitute the
chief bulk of that planet, and secondly that the temperature of
Jupiter's globe must be that which a globe of such material would have
if placed where Jupiter is. The possibility that Jupiter may be in an
entirely different stage of planetary life--or, in other words, that the
youth, middle life, and old age of that planet may belong to quite
different eras from the corresponding periods of our earth's life--is
entirely overlooked. Rather, indeed, it may be said that the extreme
probability of this, on any hypothesis respecting the origin of the
solar system, and its absolute certainty on the hypothesis of the
development of that system, are entirely overlooked.

A fair illustration of the erroneous nature of the arguments which have
been used, not only in advocating rival theories respecting the
plurality of worlds, but also in dealing with subordinate points, may be
presented as follows:

Imagine a wide extent of country covered with scattered trees of various
size, and with plants and shrubs, flowers and herbs, down to the
minutest known. Let us suppose a race of tiny creatures to subsist on
one of the fruits of a tree of moderate size, their existence as a race
depending entirely on the existence of the fruit on which they subsist,
while the existence of the individuals of their race lasts but for a few
minutes. Furthermore, let there be no regular fruit season either on
their tree or in their region of vegetable life, but fruits forming,
growing, and decaying all the time.

Let us next conceive these creatures to be possessed of a power of
reasoning respecting themselves, their fruit world, the tree on which it
hangs, and to some degree even respecting such other trees, plants,
flowers, and so forth, as the limited range of their vision might be
supposed to include. It would be a natural thought with them, when first
they began to exercise this power of reasoning, that their fruit home
was the most important object in existence, and themselves the chief and
noblest of living beings. It would also be very natural that they sh