only provides a clue to the main trend of natural processes. Although it provides us with a description of the all-pervading process of evolution and of dissolution, it does not tell us when, in the cosmic rhythm, the one or the other will predominate. Dissolution replaces evolution when the quantity of motion received is greater than the quantity dissipated, but precisely when the one process will replace the other is decided by incalculable particular conditions. When the impossibility of obtaining particular conclusions from his formula was brought to Spencer's notice, he pertinently remarked that even that exact quantitative principle—the law of gravitation—would not, by any known mathematical process, give exact results even in the simple case of three gravitating bodies, while, in a globular star cluster, it would be impossible to disentangle the complexity. From a principle so abstract as Spencer's formula only general conclusions can be expected, but even these are not without their value. And, even apart from particular deductions, there is to many minds a supreme interest in discovering a general truth, an interest which is not easy to explain to those who have it not, but which will be understood by those who value knowledge for its own sake.
To take this comparatively modest view of the value of Spencer's formula is but to class it with all other great fundamental principles, and, though Spencer attached to it greater importance than probably anyone at the present time is likely to do, he was well aware of its necessary limitations. When we realize the true nature of these evolutionary principles, when we see clearly that from the nature of the case they cannot solve all problems, we can understand the real value of this admirable, and, within reasonable limits, successful attempt to unify knowledge by showing one more common strand pervading all orders of phenomena.
Those who specialize in physical science have not yet realized the range of Spencer's conceptions so far as they can be applied to that side of human knowledge. The terminology of First Principles, as of all Spencer's work, differs from that of the special sciences. This is as it must be, the terminology of the
