174 THE GRAMMAR OF SCIENCE 



We have, then, to ask whether the boundary between 

 paper and air, if immensely magnified, would look side- 

 ways, not indeed like a geometrical line, but roughly Hke 

 the first or second of these figures : — 



Fig. 2. 



Now no direct answer can really be given to this 

 question, because bodies cease to impress us sensibly long 

 before we reach the point at which the appearance of 

 continuity might be expected to disappear. We cannot 

 predict what our sense-impressions would be if we could 

 magnify a drop of water up to the size of the earth. But 

 we may put the question in a slightly different way. We 

 may ask : Would it enable us to classify and describe 

 phenomena better if we conceived bodies to be continuous 

 as in Fig. 2, or discontinuous as in Fig. 3 ? The physicist 

 promptly replies : I can only conceive bodies to be dis- 

 continuous. Discontinuity is essential to the methods 

 by which I describe and formulate my sense-impressions 

 of the phenomenal world. 



§ 9. — Conceptual Discontinuity of Bodies. The Atom 



Foremost among the physicist's reasons for postulating 

 the discontinuity of bodies is the elasticity which we 

 notice in all of them. Air can be placed under a piston 

 in a cylinder and compressed ; a bar of wood can be bent 

 — in other words, a portion of it squeezed and another 

 portion stretched. Even the amounts by which we can 



