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258 particular sciences have reference only to the facts to be found in a certain narrow sphere, that of an objective philosophy refers to all knowledge. Readers of Spencer's work, who are particularly conversant with physics, will find much that will vitalize and illuminate their own work, especially in its most general aspects. In the sphere of physical science, Spencer's general ideas have never been developed to particular conclusions, but, if they had been, it is not unlikely that their effect might have been as great as in the life sciences. Apart from the principle of the actuality of all energy, which I have touched lightly, and the formula of evolution, which I have discussed at greater length, First Principles alone contains not a few ideas applicable to physical science. The two chapters on the "Rhythm of Motion" and "Segregration" will be found to contain thought and principles which throw some light on physical processes as yet obscure, at any rate to the extent of showing that they are particular cases of more general laws.

Those who watch the progress of chemical and physical science will note with interest the manner in which present-day developments are breaking down, one by one, the barriers which seemed to render the conception of universal evolution, of which Spencer has been the most noted exponent, more a subject for remote speculation than for present day philosophy. To the experimental genius of Sir William Ramsay and others, the seemingly impenetrable barrier presented by the chemical elements has already begun to yield. When previously we could only speculate or infer, now we know that at least some of these are elements only in the sense that their disintegration involves an energy change of a different order from that accompanying the decomposition of other substances. In the most general aspect of Spencer's ideas, the unity of all matter as of all nature, the main trend of modern thought and research confirms this fundamental principle, and, if for that alone, the most modest estimate of a work which so clearly formulated the principle of universal evolution cannot deny to it very great and permanent value.