SPACE 659 



with deformation, we can no longer by appropriate movements place 

 the organs of our body in the same relative situation with respect to 

 this body; we can no longer, therefore, reconstruct the primitive ag- 

 gregate of impressions. 



It is only later, and after a series of new experiments, that we 

 learn how to decompose a body of variable form into smaller elements 

 such that each is displaced approximately according to the same laws 

 as solid bodies. We thus distinguish " deformations " from other 

 changes of state. In these deformations each element undergoes a 

 simple change of position which may be corrected; but the modifica- 

 tion of the aggregate is more profound, and can no longer be corrected 

 by a correlative movement. Such a concept is very complex even at 

 this stage, and has been relatively slow in its appearance. It would 

 not have been conceived at all had not the observation of solid bodies 

 shown us beforehand how to distinguish changes of position. 



//, then, there were no solid bodies in nature there would be no 

 geontetry. 



Another remark deserves a moment's attention. Suppose a solid 

 body to occupy successively the positions a and /? ; in the first position 

 it will give us an aggregate of impressions A, and in the second posi- 

 tion the aggregate of impressions B. Now let there be a second solid 

 body, of qualities entirely different from the first of different color, 

 for instance. Assume it to pass from the position a, where it gives 

 us the aggregate of impressions A' to the position /?, where it gives 

 the aggregate of impressions B'. In general, the aggregate A will 

 have nothing in common with the aggregate A', nor will the aggregate 

 B have anything in common with the aggregate B'. The transition 

 from the aggregate A to the aggregate B, and that of the aggregate A' 

 to the aggregate B', are therefore two changes which in themselves have 

 in general nothing in common. Yet we consider both these changes 

 as displacements; and, further, we consider them the same displace- 

 ment. How can this be? It is simply because they may be both cor- 

 rected by the same correlative movement of our body. " Correlative 

 movement," therefore, constitutes the sole connection between two 

 phenomena which otherwise we should never have dreamed of con- 

 necting. 



On the other hand, our body, thanks to the number of its articula- 

 tion? and muscles, may have a multitude of different movements, but 

 all are not capable of " correcting " a modification of external objects; 

 those alone are capable of it in which our whole body, or at least all 

 those in which the organs of our senses enter into play are displaced 

 en bloc - i.e., without any variation of their relative positions, as in 

 the case of a solid body. 

 To sum up : 

 1. In the first place, we distinguish two categories of phenomena : 



