must have definite time-relations, so far as its changes are
concerned; but it can hardly be thought of as either going out of
existence, or as coming into existence, at any given period, though it
may completely change its form and accidents; everything basal must
have a past and a future of some kind or other, though any special
concatenation or arrangement may have a date of origin and of
destruction.

A crowd, for instance, is of this fugitive character: it assembles and
it disperses, its existence as a crowd is over, but its constituent
elements persist; and the same can be said of a planet or a sun. Yet
for some "soul" or underlying reality even in these temporary
accretions there is permanence of a sort:--Tyndall's "streak of morning
cloud," though it may have "melted into infinite azure," has not
thereby become non-existent, although as a visible object it has
disappeared from our ken and become a memory only. It is true that it
was a mere aggregate or accidental agglomeration--it had developed no
self-consciousness, nothing that could be called personality or
identity characterised it,--and so no individual persistence is to be
expected for it; yet even it--low down in the scale of being as it
is--even it has rejoined the general body of aqueous vapour whence,
through the incarnating influence of night, it arose. The thing that
_is_, both _was_ and _shall be_, and whatever does not satisfy this
condition must be an accidental or fugitive or essentially temporary
conglomeration or assemblage, and not one of the fundamental entities
of the universe. It is interesting to remember that this was one of the
opinions strongly held by the late Professor Tait, who considered that
persistence or conservation was the test or criterion of real
existence.

The question, How many fundamental entities in this sense there are,
and what they are, is a difficult one. Many people, including such
opposite thinkers as Tait and Haeckel, would say "matter" and "energy";
though Haeckel chooses, on his own account, to add that these two are
one. (Perhaps Professor Ostwald would agree with him there; though to
me the meaning is vague.) Physical science, pushed to the last resort,
would probably reply that, within its sphere of knowledge at the
present stage, the fundamental entities are _ether_ and _motion_; and
that of other things at present it knows next to nothing. If physical
science is interrogated as to the probable persistenc