458 w. WUNDT'S LOGIK, n. they withstood, or were modified by, the advance of the spirit of independent criticism. Coming to more modern times, the first prominent figure in this particular direction is that of Galileo. His principle of Conservation is passed in review ; and its relation to Newton's three laws, and in particular to the doctrine of Inertia, is considered. A considerable part of the chapter is occupied with an account of the two opposed doctrines of Momentum and Vis Viva, in the well-known dispute as to which was to be considered the truest measure of force. These are fully discussed and described, both as originally held by Leibniz and others, and also as modified by subsequent investigations. As Prof. Wundt remarks, the modern doctrine of Energy, of which that of Vis Viva was a particular dynamical case, has given a vast extension and consequent triumph to the latter. But the generalisations to which the former has given rise are by no means unimportant. In particular, the wide physical gene- ralisations, such as that which is known as the Conservation of the Moment of Momentum, and its importance in cosrnological theories (such, we may remark, as certain speculations of Mr. Herbert Spencer in this direction) are noticed. Another instruc- tive discussion is that which is devoted to the various modifica- tions of Maupertuis' Doctrine of Least Action, which Prof. Wundt maintains to have been, in its original form, an almost purely teleological principle in the way in which it regarded Nature as the great Economist of Force. The same principle is examined in the forms which it successively assumed in the hands of Laplace, Rowan Hamilton, and Jacobi. "The maximum and minimum principles have at last assumed their final form in the Principle of Least Constraint established by Gauss. According to him the movements of a system of masses, however the masses may be connected together, take place at every moment in the utmost possible agreement with their free movement, and there- fore under the least constraint. As measure of the constraint, is taken the sum of the products of every mass into the square of its departure from free motion" (p. 265). Generalisations such as those afforded by these laws of motion offer an admirable field for logical investigation in the attempt to examine their independence and comparatively fundamental or intuitive character. Though mostly too wide and abstract to lend themselves readily in any direct way to constructive pur- poses, that is, to the establishment of concrete facts, they will often serve as most convenient short cuts to the disproof of par- ticular theories or alleged facts. To take a somewhat analogous example, it is needless to remind the reader what a number of alleged inventions can be summarily dismissed by pointing out that they are at variance with the doctrine of the impossibility of t perpetual motion. The next chapter is devoted to the Logic of Physics, and covers I more nearly the ground familiar to English readers as being
