THE VALVE OF SCIENCE 89 



The three pairs of canals would have as sole function to tell us that 

 space has three dimensions. Japanese mice have only two pairs of 

 canals; they believe, it would seem, that space has only two dimensions, 

 and they manifest this opinion in the strongest way; they put them- 

 selves in a circle, and, so ordered, they spin rapidly around. The 

 lampreys, having only one pair of canals, believe that space has only 

 one dimension, but their manifestations are less turbulent. 



It is evident that such a theory is inadmissible. The sense-organs 

 are designed to tell us of changes which happen in the exterior world. 

 We could not understand why the Creator should have given us organs 

 destined to cry without cease : Eemember that space has three dimen- 

 sions, since the number of these three dimensions is not subject to 

 change. 



We must, therefore, come back to the thory of Mach-Delage. What 

 the nerves of the canals can tell us is the difference of pressure on the 

 two extremities of the same canal, and thereby: (1) the direction of 

 the vertical with regard to three axes rigidly bound to the head; (2) 

 the three components of the acceleration of translation of the center 

 of gravity of the head; (3) the centrifugal forces developed by the 

 rotation of the head; (4) the acceleration of the motion of rotation 

 of the head. 



It follows from the experiments of M. Delage that it is this last 

 indication which is much the most important; doubtless because the 

 nerves are less sensible to the difference of pressure itself than to the 

 brusque variations of this difference. The first three indications may 

 thus be neglected. 



Knowing the acceleration of the motion of rotation of the head at 

 each instant, we deduce from it, by an unconscious integration, the 

 final orientation of the head, referred to a certain initial orientation 

 taken as origin. The circular canals contribute, therefore, to inform 

 us of the movements that we have executed, and that on the same 

 ground as the muscular sensations. When, therefore, above we speak 

 of the series S or of the series 2, we should say, not that these were 

 series of muscular sensations alone, but that they were series at the 

 same time of muscular sensations due to the semicircular canals. 

 Apart from this addition, we should have nothing to change in what 

 precedes. 



In the series 8 and 2, these sensations of the semicircular canals 

 evidently hold a very important place. Yet alone they would not 

 suffice, because they can tell us only of the movements of the head; 

 they tell us nothing of the relative movements of the body, or of the 

 members in regard to the head. And more, it seems that they tell us 

 only of the rotations of the head and not of the translations it may 

 undergo. 



