of truths which hold good for all orders of phenomena, as distinct from those of the special sciences, which hold good only for limited departments, he founds his system upon the physical principles of the indestructibility of matter, and the continuity of motion, unified under the general heading of the Persistence of Force. From this is deduced the Uniformity of Law. Spencer then proceeds, in his attempt at the unification of knowledge, to seek for a law of the continuous redistribution of matter and motion, as comprising every department of the 'Knowable.' He finally reaches his famous law : — Evolution is an integration of matter and concomitant dissipation of motion ; during which the matter passes from a relatively indefinite, incoherent homogeneity to a relatively definite, coherent heterogeneity ; and during which the contained motion undergoes a parallel transformation. Evolution is supplemented by the reverse process of Dissolution ; and these formulas express the law of the entire cycle of changes passed through by every existence and at every instant, with no limitations of time or space. Evolution, however, tends ultimately to equilibrium, in which the incessant changes come to an end.
In 'The Principles of Biology 'Spencer applied the law of evolution to animate existence. He defined life in the same manner as in his 'Principles of Psychology.' As factors of evolution he not only named natural selection, or (to use Spencer's own term) survival of the fittest, but he argued strongly in favour of the direct modification of organisms by the environmental action, and also in favour of the inheritance of functionally-produced modifications. In this latter belief he is at variance with the best, though not the unanimous, opinion of modern biologists. In the second volume he promulgated the interesting theory that the shapes of animals and plants are an expression of the environmental forces which act upon them. He sets forth also his well-known law of the antagonism between individuation and reproduction. His attempt to facilitate the comprehension of heredity by supposing the existence of 'constitutional units' (first named physiological units) has attracted wide attention, and is probably not very remote from the truth.
'The Principles of Psychology' was materialistic in its general point of view for, although Spencer emphatically affirmed the existence of mind and its total distinction from matter, yet his efforts were devoted to interpreting mental manifestations by reference to physical and chemical laws. He defined life as 'the continuous adjustment of internal relations to external relations' and argued that the degree of life was proportional to the degree of correspondence between these two sets of relations. The development of memory, instinct, &c., was explained on the very questionable hypothesis that the results upon an organism of the direct action of the environment could be transmitted to its descendants. But although this attempted explanation cannot stand, it is remarkable that an evolutionary basis is given to the whole work, of which the first edition had appeared four years before Darwin published his great book. In the analytical portions he attributes all acts of intelligence to the variously compounded consciousnesses of relations of likeness and unlikeness. Finally he sets forth his famous ' Universal Postulate 'to the effect that the criterion of the truth of a proposition is the inconceivability of its negation. Opinion still differs as to the merits of many parts of this work. Doubtless much of the detail and some of the principles are erroneous ; but much has become generally accepted ; and in view of the state of knowledge at the time when it was written, it must be considered a masterpiece.
'The Principles of Sociology' begins by an exposition of the so-called 'Ghost Theory,' in which Spencer regards all primitive mythological beliefs as modified forms of ancestor-worship. In the part dealing with 'The Inductions of Sociology' he minutely draws the analogy between the social and physical organism. The remaining volumes of the work deal with ceremonial institutions, political institutions, ecclesiastical institutions, professional institutions, industrial institutions. The general result is to distinguish between two main types of society, the militant resting on a basis of status, and the industrial resting on a basis of contract.
'The Principles of Ethics ' was considered by Spencer as the flower of the whole philosophy. His system is hedonistic, in so far as it regards happiness as the object to be attaint ; it is evolutionary, in so far as it represents that evolution is carrying us to a state in which happiness will far exceed what we now experience. The utilitarians are attacked on the ground that, in their enthusiasm for altruism, they attach insufficient importance to a ational egoism. In the second volume, part iv., 'Justice,' is Spencer's final and
