As conceptional knowledge is based on perceptional knowledge, and we can only perceive about six times per second, and as the principal forms of knowledge are gained through the eye, we are conceiving progress in phenomena under a very restricted outlook; we cannot recognise such slow motions as, for instance, the hour-hand of a watch, the growth of a tree, or rise of the tide, except by noting the change that has occurred after a long interval; there is therefore a whole world of events which we cannot see. Owing to this limit, in our unit of time perception, we also cannot perceive events which are taking place beyond a certain quickness, they become blurred and give the impression of continuity, and constitute another world of events lost to us. For the same reason there is a whole world of sensation lost to us by our limited unit of sound perception; we cannot follow separate sound-events if they occur quicker than sixteen in a second, beyond that they become blurred and give the impression of continuity. If, on the other hand, our units of perception were increased a thousandfold, as is probably the case with some insects, our conscious lives would contain a thousand more events than they do at present, and, as the consciousness of length of life is dependent upon the number of events that have been perceived, we should under these conditions have passed on this earth a life equivalent to, say, 70,000 years under our present restricted unit; every second of that long period would have been as full of events for us as is a second in our present life of seventy years. If, on the other hand, our unit of perception were decreased a thousandfold, our length of life, based upon perception of events, would be no longer than 25-1/2 of our present days; if our life were actually reduced to that period (so as to regain our present units of perception) we should be old and grey-headed before the sun had risen for the twenty-fifth time since our birth. If our unit of perception, with our length of life, were again reduced a thousandfold, the whole of our life of seventy years would now only be equal to forty-three minutes, and, in the whole of that life, we could only see the sun move ten degrees, namely, twenty of its own diameters in the heaven; if we were born, say, at noon on midsummer's day, we could never have any idea of anything but daytime, and neither our fathers, nor grandfathers, nor great-grandfathers for fifteen generations before them could have seen the sun rise; but there would have been a tradition, handed down from a far distant past generation, that a long time ago, beyond the memory of man, there was no sun at all, everything was pitch dark, and that time was called the "Great Shadow." If their records could have gone still further back for the same length of time they would have heard that, before the "Great Shadow," the sun was always shining in the heavens, and that