We can measure Time in one way only—by counting repeated motions. Apart from the operation of the physical Law of Periodicity we should have no natural measures of Time. If that statement be true it follows that apart from the operation of this law we could not attain to any knowledge of Time.[11:1] Perhaps this latter proposition may not at first be readily granted. Few, probably, would hesitate to admit that in a condition in which our experience was a complete blank we should be unable to acquire any knowledge of Time; but it may not be quite so evident that in a condition in which experience consisted of a multifarious but never repeated succession of impressions the Knowledge of Time would be equally awanting.[12:1] Yet so it is. The operation of the Law of Periodicity is necessary to the measurement of Time. It is by means, and only by means, of periodic pulsative movements that we ever do or can measure Time. Now, apart from some sort of measurement Time would be unknowable. A time which was neither long nor short would be meaningless. The idea of unquantified Time cannot be conceived or apprehended. Time to be known must be measured.

Periodicity, therefore, is essential to our Knowledge of Time. But Nature amply supplies us with this necessary instrument. The Law of Periodicity prevails widely throughout Nature. It absolutely dominates Life.

The centre of animal vitality is to be found in the beating heart and breathing lungs. Pulsation qualifies not merely the nutrient life but the musculo-motor activity as well. Eating, Walking,—all our most elementary movements are pulsatory. We wake and sleep, we grow weary and rest. We are born and we die, we are young and grow old. All animal life is determined by this Law.

Periodicity—generally at a longer interval of pulsation—equally affects the vegetal forms of life. The plant is sown, grows, flowers, and fades.

Periodicity is to us less obvious in the inanimate world of molecular changes; yet it is in operation even there. But it is more especially in the natural motions of those so-called material masses which constitute our physical environment that Periodicity most eminently prevails. Indeed it was by astronomers that the operation of this Law was first definitely recognised and recorded. Periodicity is the scientific name for the Harmony of the Spheres.

The two periodic motions which most essentially affect and concern us human beings are necessarily the two periodic motions of the globe which we inhabit—its rotation upon its axis which gives us the alternation of Day and Night, and its revolution round the Sun which gives us the year with its Seasons. To the former of these, animal life seems most directly related; to the latter, the life of the vegetal orders. It is evident that the forms of animal life on the globe are necessarily determined by the periodic law of the Earth's diurnal rotation. This accounts for the alternations of waking and sleeping, working and resting, and so forth. In like manner the more inert vitality of the vegetable kingdom is determined by the periodic law of the Earth's annual revolution. When fanciful speculators seek to imagine what kind of living beings might be encountered on the other planets of our system, they usually make calculations as to the force of gravity on the surface of these planets and conjure up from such data the possible size of the inhabitants, their relative strength and agility of movement, etc. So far so good. But the first question we should ask, before proceeding to our speculative synthesis, should rather be the length of the planet's diurnal rotation and annual revolution periods. Certain planets, such as Mars and Venus, have rotation periods not very different from those of our own Earth.[14:1] Other things being equal, therefore, a certain similarity of animal life must be supposed possible on these planets. On the other hand, the marked difference in their revolution period would lead us to expect a very wide divergence between their lower forms of life, if any such there be, and our own terrestrial vegetation. The shorter the annual period the more would the vegetal approximate to the animal, and vice versa. It would, however, be foolish to waste more time over a speculation so remote.

But these two facts remain unshaken:—(1) That our measurements and whole science of Time depend absolutely on the operation throughout Nature of the Law of Periodicity, and (2) that the periodicities which affect and determine animal and vegetal life upon our Earth are the periodic movements of rotation and revolution of that Earth itself.

Now it is to the curvilinear motions of the heavenly bodies that we must ascribe our subjection to the periodic law. If these heavenly bodies moved for ever in straight lines, as they would do if unacted on by natural forces, the periodic rhythm of Nature would disappear.

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.

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