ing scheme fitted to the new state of knowledge developed. The method is specially applicable to elaborate inquiries, particularly those in which the premises are imperfect and a long logical chain is hung upon them. The discussions of our great fundamental conceptions furnish the best examples, chiefly examples of the lack of a systematic regenerative method. Among these, two general classes may be recognized, (1) those of a rather rigorous type, as, for a distinguished example, the researches of George Darwin on tidal reaction and the history of the earth and moon, and (2) those of a looser and sometimes rather metaphysical type, which I shall try to illustrate by the doctrine of determinism. In all cases, assumptions are made the basis of the procedure. Absolute premises are not available. Taking its start from these assumptions, the process pursues a long course and at the end conclusions of great import are often drawn. Usually the process rests there, and in this lies a serious shortcoming. It should give rise to a new process of a higher order. Not seldom, a critical study of the results will reveal features that were not recognized nor suspected in the original assumptions, though really there. Out of these revelations should grow new assumptions and a new process. The second conclusion may in like manner betray unsuspected qualities and these should beget still other assumptions, and so the procedure should continue until the field is exhausted.
To choose a specific illustration is not a little delicate, for to be most familiar it must be of the negative type, but I fear such an illustration is the only way to clearly convey the meaning here intended. I therefore venture to choose one so eminent and so admirable, even with its limitations, that any suggestion of shortcoming will in no wise dim the luster of a great achievement. In the classic investigations of George Darwin on tides and their astronomic consequences, a viscous earth is assumed as the starting-point, with properties such that the tidal protuberance is carried forward by the rotation of the earth to the point which gives the maximum effect on the motions of the earth and moon. These assumptions run potentially through the whole train of brilliant mathematical deduction. At the end of the inquiry, or if not of this particular inquiry, at least of collateral inquiries, the conclusion is reached that the earth is a rigid body comparable to steel. Between such a rigid body and such a viscous earth as was assumed at the outset of the inquiry, there is a seeming incongruity. This, under the regenerative method, suggests a new investigation on the assumption that the earth is a very rigid body, with the further assumption that it has high elasticity of form, such that its protuberance may perhaps not be carried forward to the degree previously postulated. These new assumptions are the more imperative, because they are supported by inquiries based on quite independent lines. In framing the new hypothesis an advance in detail and in organization is to be sought on the evolutionary principle already in-
