1. The external senses in their different degrees, especially sight and touch, give us the knowledge of objects that are _extended_ and figured. The body I grasp with the hand or survey with the eye has limits, outlines, angles, surfaces--that is, it has more or less EXTENSION. The inner sense gives us the knowledge of the changes and successions of our mental life. But, amid all these changes, I am conscious there is a something which _endures_. What is that permanent something which I apprehend under all the varying mental states? It is that principle of personal identity which I call _I_--_myself_. To feel and know that I am the same person under all modifications of my mental activity is to _endure_. Through the aid of memory, which enables me to recall past mental states, and the immediate consciousness of personal existence, through all these changes I obtain the notion of DURATION. The notions of Extension and Duration are clear to my mind. 2. Besides the notion of extended bodies, I have also the notion of position, distance, direction among extended bodies. They exist in various relations to each other; they are here or there, above or below, near at hand or indefinitely remote. It may be the distance between two particles of dust in the sunbeam, or the walls of the room, or between the earth and the sun, or between the sun and the outermost planet of our system, or between the earth and the remotest star which twinkles at the outposts of the universe. Position, distance, direction are all _relations_. And to all these relations I prefer, with Sir John Herschel, to give the generic name SPACE.[111] Then I have no confusion of thought, and no difficulty or contradiction in using the language of Cousin, Hamilton, and McCosh, when they speak of "determinate and limited space," "particular spaces," "parts of space," and "proportions of space." Along with the notion of duration (and succession of different states in the same existence), I am conscious that this duration is capable of admeasurement by common standards, and ideally divided into periods of longer or shorter duration. This duration may be measured by successive states of consciousness, or facts of domestic history, or, better still, by the succession of day and night, or the relative position of the sun in the heavens, the revolutions of the moon around the earth, or of the earth around the sun. These are really world-measurements of duration. Since, then, duration can be measured from any point and in any proportions, it is clear that measurement is a purely relative thing--a relation. Of any such thing as "pure time" or "absolute time" we have no knowledge. TIME _is the measure of finite duration_--the correlation of things successive. And if I confine myself to this usage, I am under no necessity of using the paradoxical language of many philosophers, "time is eternity!"