iracle.
We do not know what to expect from it. But when we can
place a phenomenon under a general law, applicable in a wide
variety of instances, everything that can be said of all the
other instances in which the law applies, applies also to this
particular case.

Think of heat as motion, and whatever is true of motion will be
true of heat; but we have had a hundred experiences of motion for
everyone of heat. Think of the rays passing through this lens as
bending toward the perpendicular, and you substitute for the
comparatively unfamiliar lens the very familiar notion of a particular
change in direction of a line, of which motion every day brings us
countless examples.[1]

[Footnote 1: James: _Psychology_, vol. II, p. 342.]

It must be noticed that the explanation which science gives,
is really in answer to the question, "How?" not the question,
"Why?" We are said to understand phenomena when
we understand the laws which _govern_ them. But to say that
certain given phenomena--the appearance of dew, the falling
of rain, the flash of lightning, the putrefaction of animal
matter--_obey_ certain laws is purely metaphorical. Phenomena
do not _obey_ laws in the sense in which we say the child
follows the commands of his parents, or the soldier those of
his officer. The laws of science simply describe the relations
which have repeatedly been observed to exist between phenomena.
They are laws in the sense that they are invariably
observed successions. When it has been found that
whenever _A_ is present, _B_ is also present, that the presence of
_A_ is always correlated with the presence of _B_, and the
presence of _B_ is always correlated with the presence of _A_, we say
we have discovered a scientific law.

Science thus explains in the sense that it reduces the multiplicity
and variety of phenomena to simple and general laws.
The ideal of unity and simplicity is the constant ideal toward
which science moves, and its success in thus reducing the miscellaneous
facts of experience has been phenomenal. The
history of science in the nineteenth century offers some
interesting examples. The discovery of the conservation of
energy and its transformations has revealed to us the unity
of force. It has shown, for example, that the phenomenon of
heat could be explained by molecular motions. "Electricity
annexed magnetism." Finally the relations of electricity and
light are now known; "the three realms of light, of electricity