edge consists in
systematic classification. Thus if we observe the heavenly bodies
individually we can state merely that they have been observed to have
certain motions through the sky, that they are luminous, and the like.
If, however, we compare them one with another, we discover that, whereas
all partake in the general movement of the heavens, some have a movement
of their own. Thus we arrive at a system of classification according to
motion, by which fixed stars are differentiated from planets. A further
classification according to other criteria gives us stars of the first
magnitude and stars of the second magnitude, and so forth. We thus
arrive at a systematic understanding expressed in laws by the
application of which accurate forecasts of celestial phenomena can be
made. Classification in the strict logical sense consists in discovering
the casual interrelation of natural objects; it thus differs from what
is often called "artificial" classification, which is the preparation,
e.g. of statistics for particular purposes, administrative and the like.

Of the systems of classification adopted in physical science, only one
requires treatment here, namely, the classification of the sciences as
a whole, a problem which has from the time of Aristotle attracted
considerable attention. Its object is to delimit the spheres of
influence of the positive sciences and show how they are mutually
related. Of such attempts three are specially noteworthy, those of
Francis Bacon, Auguste Comte and Herbert Spencer.

Bacon's classification is based on the subjective criterion of the
various faculties which are specially concerned. He thus distinguished
History (natural, civil, literary, ecclesiastical) as the province of
memory, Philosophy (including Theology) as that of reason, and Poetry,
Fables and the like, as that of imagination. This classification was
made the basis of the _Encyclopedie_. Comte adopted an entirely
different system based on an objective criterion. Having first
enunciated the theory that all science passes through three stages,
theological, metaphysical and positive, he neglects the two first, and
divides the last according to the "things to be classified," in view of
their real affinity and natural connexions, into six, in order of
decreasing generality and increasing complexity--mathematics, astronomy,
physics, chemistry, physiology and biology (including psychology), and
sociology. This he conceives to be no