It is to the fact that all Nature is under the constraint due to the constant silent operation of physical Force that we owe, therefore, the law which determines the most essential features of vitality. The pulsations in which life consists and by which it is sustained are attributable to the constraint and limitation which we recognise as the effect of the operation of Natural Force. It is to this same cause that we ascribe the resistance of cohering masses in virtue of which sensation arises and by which our experience is punctuated. It is by means of these obstructions to free activity that our experience is denoted, and by reference to these that it is cognised. Indeed, Activity itself as we know it depends upon and presupposes the existence of these cohering masses. Thus the operation of Natural Force and the constraint and limitation which are thereby imposed upon our activity appear at once to determine the conditions of life and to furnish the fundamental implements of Knowledge. We cannot overleap the barriers by which Life is constrained. These, whilst, on the one hand they seem to _create the environment_ which sustains Life, on the other hand seem to impose upon it the limitations under which it inevitably fails and dies. We cannot even in imagination conceive, either as reality or as fancy, the illimitable puissance of a Life perfectly free and unrestrained. Yet the assurance that Perfect Love could overcome the bonds of Materiality and Death encourages in mankind the Hope of an existence beyond the impenetrable veil of physical limitation. And this at any rate may be admitted, namely, that that dynamic condition in which materiality arises is also the condition-precedent of Tridimensionality, of Force, of Time, and of Mutation. But we cannot thus account for the _elan vital_ itself. FOOTNOTES: [11:1] Plato in the dialogue _Timæus_ tells us that Time was born with the Heavens, and that Sun, Moon, and Planets were created in order that Time might be. [12:1] This might be contrasted with the statement of M. Bergson who tells us (_Evolution créatrice_, p. 11): "Plus nous approfondirons la nature du temps plus nous comprendrons que durée signifie invention, création de formes, elaboration continue de l'absolument nouveau." [14:1] Recently, we believe, astronomers have favoured the view that the day of Venus is equal in length to her year. II THE ORIGIN OF PHYSICAL CONCEPTS