is without bounds the stellar universe also extends to infinity.
For in this case the reproduction of nebulous masses fit for
generating new systems of worlds must go on through space that is
endless, and consequently the process can never come to an end
and can never have had a beginning. We have, therefore, three
alternatives: either the visible universe is finite, while the
ether is infinite; or both are finite; or both are infinite. Only
on the first supposition, I think, do we get a universe which
began in time and must end in time. Between such stupendous
alternatives we have no grounds for choosing. But it would seem
that the third, whether strictly true or not, best represents the
state of the case relatively to our feeble capacity of
comprehension. Whether absolutely infinite or not, the dimensions
of the universe must be taken as practically infinite, so far as
human thought is concerned. They immeasurably transcend the
capabilities of any gauge we can bring to bear on them.
Accordingly all that we are really entitled to hold, as the
outcome of sound speculation, is the conception of innumerable
systems of worlds concentrating out of nebulous masses, and then
rushing together and dissolving into similar masses, as bubbles
unite and break up--now here, now there--in their play on the
surface of a pool, and to this tremendous series of events we can
assign neither a beginning nor an end.

[3] Fortnightly Review, April, 1875.


We must now make some more explicit mention of the ether which
carries through space the rays of heat and light. In closest
connection with the visible stellar universe, the vicissitudes of