88 POPULAR SCIENCE MONTHLY 



Yes, but it is experience which has taught us the laws of motion of a 

 rigid solid; nothing would prevent our imagining them different. To 

 sum up, for me to imagine that I get out of my prison, I have only to 

 imagine that the walls seem to open, when I move. 



I believe, therefore, that if by space is understood a mathematical 

 continuum of three dimensions, were it otherwise amorphous, it is the 

 mind which constructs it, but it does not construct it out of nothing; 

 it needs materials and models. These materials, like these models, 

 preexist within it. But there is not a single model which is imposed 

 upon it; it has choice; it may choose, for instance, between space of 

 four and space of three dimensions. What then is the role of experi- 

 ence? It gives the indications following which the choice is made. 



Another thing: whence does space get its quantitative character? 

 It comes from the role which the series of muscular sensations play 

 in its genesis. These are series which may repeat themselves, and it 

 is from their repetition that number comes; it is because they can 

 repeat themselves indefinitely that space is infinite. And finally we 

 have seen, at the end of section 3, that it is also because of this that 

 space is relative. So it is repetition which has given to space its essen- 

 tial characteristics; now, repetition supposes time; this is enough to 

 tell that time is logically anterior to space. 



§ 7. Role of the Semicircular Canals 

 I have not hitherto spoken of the role of certain organs to which 

 the physiologists attribute with reason a capital importance, I mean 

 the semicircular canals. Numerous experiments have sufficiently 

 shown that these canals are necessary to our sense of orientation; but 

 the physiologists are not entirely in accord; two opposing theories have 

 been proposed, that of Mach-Delage and that of M. de Cyon. 



M. de Cyon is a physiologist who has made his name illustrious by 

 important discoveries on the innervation of the heart; I can not, how- 

 ever agree with his ideas on the question before us. Not being a physi- 

 ologist, I hesitate to criticize the experiments he has directed against 

 the adverse theory of Mach-Delage; it seems to me, however, that they 

 are not convincing, because in many of them the total pressure was 

 made to vary in one of the canals, while, physiologically, what varies 

 is the difference between the pressures on the two extremities of the 

 canal; in others the organs were subjected to profound lesions, which 

 must alter their functions. 



Besides, this is not important; the experiments, if they were irre- 

 proachable, might be convincing against the old theory. They would 

 not be convincing for the new theory. In fact, if I have rightly under- 

 stood the theory, my explaining it will be enough for one to understand 

 that it is impossible to conceive of an experiment confirming it. 



