sal as a whole of the truth that they may express.

[Sidenote: Natural Science is Abstract.]

Sect. 51. The impossibility of embracing the whole of knowledge within
natural science is due to the fact that the latter is _abstract_. This
follows from the fact that natural science is governed by a selective
interest. The formulation of definitions and laws in exclusively
mechanical terms is not due to the exhaustive or even pre-eminent
reality of these properties, but to their peculiar serviceableness in a
verifiable description of events. Natural science does not affirm that
reality is essentially constituted of matter, or essentially
characterized by motion; but is _interested_ in the mechanical aspect of
reality, and describes it quite regardless of other evident aspects and
without meaning to prejudice them. It is unfortunately true that the
scientist has rarely been clear in his own mind on this point. It is
only recently that he has partially freed himself from the habit of
construing his terms as final and exhaustive.[137:5] This he was able
to do even to his own satisfaction, only by allowing loose rein to the
imagination. Consider the example of the atomic theory. In order to
describe such occurrences as chemical combination, or changes in volume
and density, the scientist has employed as a unit the least particle,
physically indivisible and qualitatively homogeneous. Look for the atom
in the body of science, and you will find it in physical laws governing
expansion and contraction, and in chemical formulas. There the real
responsibility of science ends. But whether through the need of popular
exposition, or the undisciplined imagination of the investigator
himself, atoms have figured in the history of thought as round
corpuscles of a grayish hue scurrying hither and thither, and armed with
special appliances wherewith to lock in molecular embrace. Although this
is nonsense, we need not on that account conclude that there are no
atoms. There are atoms in precisely the sense intended by scientific
law, in that the formulas computed with the aid of this concept are true
of certain natural processes. The conception of ether furnishes a
similar case. Science is not responsible for the notion of a quivering
gelatinous substance pervading space, but only for certain laws that,
_e. g._, describe the velocity of light in terms of the vibration. It is
true that there is such a thing as ether, not as gratuitously rounded
o