ORIGIN OF PHYSICAL CONCEPTS 23 



before us in immense multitude, each distinct 

 from its adjacent neighbour, yet all inter- 



/ related as parts of one single whole the 

 presentation thus constituting what is called 

 Extensity. 



This is the most commonly employed meaning 

 of the term spatial. Yet it is evidently in its 



/ origin rather temporal than spatial. In ordinary 

 movement we encounter by touch various obstacles, 

 but only a very few of these impress us at any 

 one moment of time. On the contrary, they 

 succeed one after the other. To the blind, there- 

 fore, as Platner long ago remarked : Time serves 

 instead of Space. In Vision, on the other hand, a 

 large number, which it would take a very long 

 time to encounter in touch, are presented simul- 

 taneously. In this there is an immense practical 

 advantage, the result being that we come habitu- 

 ally to direct our every action by reference to 

 the data of Sight. Now it is because these data 

 so simultaneously presented are employed by us 

 as the guides of action that their presentation 

 acquires the character which we denominate Ex- 

 tensity. The simultaneous occurrence of a large 

 number of Sounds does not seem to us to present 

 such a character. But let us suppose that all the 

 objects which constitute obstacles to our Activity 



