CHAP. VIII.] ESSAYS AT CAMBRIDGE. 237 



being, but yet it is very difficult to do so. Some count by 

 heads, others by souls, others by noses; still there is a 

 tendency either to run together into masses or to split up 

 into limbs. The dimmed outlines of phenomenal things all 

 merge into another unless we put on the focussing glass of 

 theory and screw it up sometimes to one pitch of definition, 

 and sometimes to another, so as to see down into different 

 depths through the great millstone of the world. 



" As for space and time, any man will tell you that ' it 

 is now known and ascertained that they are merely modifica- 

 tions of our own minds.' And yet if we conceive of the 

 mind as absolutely indivisible and capable of only one state 

 at a time, we must admit that these states may be arranged 

 in chronological order, and that this is the only real order of 

 these states. For we have no reason to believe, on the 

 ground of a given succession of simple sensations, that 

 differences in position, as well as in order of occurrence, 

 exist among the causes of these sensations. But yet we 

 are convinced of the co-existence of different objects at the 

 same time, and of the identity of the same object at different 

 times. Now if we admit that we can think of difference 

 independent of sequence, and of sequence without difference, 

 we have admitted enough on which to found the possibility 

 of the ideas of space and time. 



" But if we come to look more closely into these ideas, 

 as developed in human beings, we find that their space has 

 triple extension, but is the same in all directions, without 

 behind or before, whereas time extends only back and for- 

 ward, and always goes forward. 



" To inquire why these peculiarities of these fundamental 

 ideas are so would require a most painful if not impossible 

 act of self-excenteration ; but to determine whether there is 

 anything in Nature corresponding to them, or whether they 

 are mere projections of our mental machinery on the surface 

 of external things, is absolutely necessary to appease the 

 cravings of intelligence. Now it appears to me that when 

 we say that space has three dimensions, we not only express 

 the impossibility of conceiving a fourth dimension, co-ordi- 



