brations between constitution and conditions, between the
structure of society and the nature of its members, between fertility
and mortality, advance simultaneously towards a common climax. In
approaching an equilibrium between his nature and the ever-varying
circumstances of his inorganic environment, and in approaching an
equilibrium between his nature and all the requirements of the social
state, man is at the same time approaching that lowest limit of
fertility at which the equilibrium of population is maintained by the
addition of as many infants as there are subtractions by death.

V.

Next in logical order and in order of publication come the two volumes
collectively entitled "The Principles of Psychology." In these volumes
an attempt is made to trace objectively the evolution of mind from
reflex action through instinct to reason, memory, feeling, and will,
from the interaction of the nervous system with its environment.
Subjectively, mental states are analyzed, and it is contended that all
of them--including those primary scientific ideas, the perceptions of
matter, motion, space, and time, assumed in the "First Principles"--can
be analyzed into a primitive element of consciousness, something which
can be defined only as analogous to a nervous shock. These perceptions
have now become innate in the individual. They may be called--as Kant
called space and time--forms of intuition; but they have been acquired
empirically by the race, through the persistence of the corresponding
phenomena in the environment, and from the accumulated experiences of
each individual being transmitted in the form of modified structure to
his descendants. This principle of heredity is one of the laws by which
individuals are connected with one another into an organic whole; and we
thus pass to what Spencer calls superorganic evolution, implying the
co-ordinated actions of many individuals, and giving rise to the science
of sociology.

It is this science which Mr. Spencer undertakes to expound in the three
volumes entitled the "Principles of Sociology." The first of these
volumes presents a statement of the several sets of factors entering
into social phenomena. These factors are, first, human ideas and
feelings considered in their necessary order of evolution; secondly,
surrounding natural conditions; and, thirdly, those ever-complicating
conditions to which society itself gives origin. Under the caption "The
Inductions of Sociol