SPACE AND TIME 189 



can measure millions of years, fails us when we once doubt 

 its regularity. Why should a year now represent the same 

 amount of consciousness as it might have done a few 

 million years back ? The absolutely uniform motion by 

 which alone we could reach an absolute measurement of 

 time fails us in perceptual experience. It is, like the 

 geometrical surface, reached in conception, and in con- 

 ception only, by carrying to a limit there the approximate 

 sameness and uniformity which we observe in certain 

 perceptual motions. Absolute intervals of time are the 

 conceptual means by which we describe the sequence of 

 our sense -impressions, the frame into which we fit the 

 successive stages of the sequence, but in the world of 

 sense-impression itself they have no existence. 



Newton, defining what we term here conceptual time, 

 tells us : — 



" That absolute, true, and mathematical time is con- 

 ceived as flowing at a constant rate, unaffected by the 

 speed or slowness of the motions of material things." 



Clearly such time is a pure ideal, for how can we 

 measure it if there be nothing in the sphere of perception 

 which we are certain flows at a constant rate ? " Uniform 

 flow," like any other scientific concept, is a limit drawn in 

 imagination — in this case, from the actual "speed or slow- 

 ness of the motions of material things." But, like other 

 scientific concepts, it is invaluable as a shorthand method 

 of description. Perceptual time is the pure order in suc- 

 cession of our sense-impressions and involves no idea of 

 absolute interval. Conceptual time is like a piece of 

 blank paper ruled with lines at equal distances, upon 

 which we may inscribe the sequence of our perceptions, 

 both the known sequence of the past and the predicted 

 sequence of the future. The fact that upon the ruled 

 lines we have inscribed some standard recurrincr sense- 

 impression (as the daily transit of a heavenly body over 

 the meridian of Greenwich), must not be taken as signify- 

 ing that states of consciousness succeed each other 

 uniformly, or that a " uniform flow " of consciousness is in 

 some way a measure of absolute time. It denotes no 



