this so-called law of gravitation to cease to operate, the entire
plan of our universe would be sadly disarranged. The earth, for example,
and the other planets would leave their elliptical orbits and hurtle
away on a tangential course. We should soon be beyond the reach of the
sun's beneficent influence; an arctic chill would pervade polar and
tropical regions alike, and the term of man's existence would
come suddenly to a close. Here, then, is a force at once the most
comprehensible and most important from a human stand-point that can be
conceived; yet it cannot be too often repeated, we know nothing whatever
as to the nature of this force. We do not know that there may not be
other starlike clusters beyond our universe where this force does not
prevail. We do not know that there may not come a period when this force
will cease to operate in our universe, and when, for example, it will be
superseded by the universal domination of a force of mutual repulsion.
For aught we know to the contrary, our universe may be a pulsing
organism, or portion of an organism, all the particles of which are at
one moment pulled together and the next moment hurled apart--the moments
of this computation being, of course, myriads of years as we human
pygmies compute time.

To us it would be a miracle if a heavy body, unsupported, should fly off
into space instead of dropping towards the centre of the earth; yet the
time may come when all such heavy objects will thus fly off into space,
and when the observer, could there be such, must marvel at the miracle
of seeing a heavy object fall towards the earth. Such thoughts as these
should command the attention of every student of science who would
really understand the meaning of what are termed natural laws. But, on
the other hand, such suggestions must be held carefully in check by the
observation that scientific imagining as to what may come to pass at
some remote future time must in no wise influence our practical faith
in the universality of certain natural laws in the present epoch. We may
imagine a time when terrestrial gravitation no longer exerts its power,
but we dare not challenge that power in the present. There could be no
science did we not accept certain constantly observed phenomena as the
effect of certain causes. The whole body of science is made up solely of
such observations and inferences. Natural science is so called because
it has to do with observed phenomena of nature.