We can only measure time by _uniform_ motion. Observe the vicious circle. Uniform motion means the covering of equal spaces in equal times. But how are we to determine our equal times? Ultimately we have no other criterion save the uniform motion of the clock-hand or the star dial. The very expressions, "uniform motion," "equal times," beg the whole question of the nature of time. Let us then, in this predicament, consider time not from the standpoint of experiment, but of conscious experience--what Bergson calls "real duration." Every point along the line of memory, of conscious experience, has been traced out by that unresting stylus we call "the present moment." The question of its rate of motion we will not raise, as it is one with which we have found ourselves impotent to deal. We believe on the best of evidence that the conscious experience of others is conditioned like our own. For better understanding let us have recourse to a homely analogy: let us think of these more or less parallel lines of individual experience in the semblance of the strands of a skein of flax. Now if, _at the present moment_, this skein were cut with a straight knife at right angles to its length, the cut end would represent the _time plane_--that is, the present moment of all--and it would be the same for all providing that the time plane were flat _But is it really flat_? Isn't the straightness of the knife a mere poverty of human imagination? Existence is always richer and more dramatic than any diagram. "Line in nature is not found; Unit and universe are round. In vain produced, all rays return; Evil will bless and ice will burn." Undoubtedly the flat time-plane represents with fair accuracy the temporal conditions that obtain in the human aggregate in this world under normal conditions of consciousness, but if we consider our relation to intelligent beings upon distant worlds of the visible universe the conditions might be widely different The time section corresponding to what our straight knife made flat in the case of the flax may be--nay, probably is--strongly curved. RELATIVITY This crude analogy haltingly conveys what is meant by curved time. It is an idea which is implicit in the Theory of Relativity. This theory has profoundly modified many of our basic conceptions about the universe in which we are immersed. It is outside the province of this book and beyond the power of its author even so much as to sketch the main outlines of this theory, but certain of its conclusions are indispensable, since they baldly set forth our dilemma in regard to the measurement of space and time. We can measure neither except relatively, because they must be measured one by the other, and no matter how they vary, these variations always compensate one another, leaving us in the same state of ignorance that we were in before.