THE RELATIVITY OF SPACE. 109 



planets would be replaced by little balls, while on 

 one of these little balls there would move a Lilliputian 

 that I should call myself. But this act of imagination 

 would be impossible for me if I had not previously 

 constructed my restricted space and my extended 

 space for my personal use. 



IV. 



Now we come to the question why all these spaces 

 have three dimensions. Let us refer to the " distribu- 

 tion board " spoken of above. We have, on the one 

 side, a list of the different possible dangers — let us 

 designate them as Ai, A2, etc. — and, on the other side, 

 the list of the different remedies, which I will call in 

 the same way Bi, B2, etc. Then we have connexions 

 between the contact studs of the first list and those of 

 the second in such a way that when, for instance, the 

 alarm for danger A3 works, it sets in motion or 

 may set in motion the relay corresponding to the 

 parry B4. 



As I spoke above of centripetal or centrifugal wires, 

 I am afraid that all I have said may be taken, not as 

 a simple comparison, but as a description of the 

 nervous system. Such is not my thought, and that 

 for several reasons. Firstly, I should not presume to 

 pronounce an opinion on the structure of the nervous 

 system which I do not know, while those who have 

 studied it only do so with circumspection. Secondly, 

 because, in spite of my incompetence, I fully realize 

 that this scheme would be far too simple. And lastly, 

 because, on my list of parries, there appear some that 

 are very complex, which may even, in the case of 

 extended space, as we have seen above, consist of 



