THE modern philosophy of physical science leans strongly to the view, so well expressed by a recent writer, that the concept is synonymous with the corresponding set of operations. The idea of mechanical imagery advocated by Lord Kelvin is thus being replaced by the notion of an operational process which accordingly presupposes the existence of a law of transformation. To mathematicians, this aspect has long been the subject of profound study, but not until comparatively recently has the idea permeated the theoretical domain of science.
The Theory of Linear Operators:
from the Standpoint of Differential Equations of Infinite Order. By Harold T. Davis. (Monograph of the Waterman Institute of Indiana University, Contribution No. 72.) Pp. xiv + 628. (Bloomington, Ind.: The Principia Press; London: Williams and Norgate, Ltd., 1936.) 35s. net.