The word “classification” is used here in its sense of “the result of classifying” rather than the action of so doing. Since the resulting classification has special reference to the subject-matter of science as a whole, it is natural to turn to the scientific literature of various periods for an indication of how this classification has been developed. For sake of comparison, reference may be made to one of the modern systems of library classification. In the Dewey Decimal System the numbers 550 to 559 are allotted to Geology and 560 to 569 to Palaeontology. By placing numbers to the right of the decimal point, further sub-divisions may be made, for example, 560·942 is classed as Palaeon-tology of England. Thus a number is available for every reasonable demand of classification. The present purpose is to trace the natural evolution of the various branches of science, in contrast to the mechanical process of providing a classification of scientific literature for ease of reference. An example may make this distinction clearer.
