ORIGIN OF PHYSICAL CONCEPTS 29 



(1) The force of gravity. This force constantly 

 operating constrains the organism to be in constant 

 contact with the earth on which we live. But, 

 further, it gives us the definite idea of Direction. It 

 is from the action of gravity that we derive our 

 distinction between Up and Down from which 

 as a starting-point we build up our conception 

 of tridimensional Space. And in this respect it 

 must be remembered that as the areas of spheres 

 are proportional to the squares of their radii it 

 necessarily follows that gravity if it acts uniformly 

 in tridimensional Space must vary in intensity in 

 proportion to the square of the distance of the point 

 of application from the centre of origin. Gravity and 

 tridimensionality are in short necessarily connected. 



(2) The same law which determines the force of 

 gravity seems to determine also the force of cohesion, 

 and therefore the form of material bodies. These, 

 therefore, are necessarily subject also to tridimension- 

 ality, and in the force which generates solid form we 

 find a second source of our elementary spatial ideas. 



Such form is the expression of an obstacle to 

 action which determines all our movements, and 

 in which we discover those forms of the limitations 

 of activity which we call spatial characters. 



(3) Organic Dualism is a third determinant of 

 activity, and thus also a source of spatial ideas. 



