28o THE GRAMMAR OF SCIENCE 



If we take a piece of any substance, say a bit of chalk, 

 and divide it into small fragments, these still possess the 

 properties of chalk. Divide any fragment again and 

 again, and so long as a divided fragment is perceptible by 

 aid of the microscope it still appears chalk. Now the 

 physicist is in the habit of defining the smallest portion 

 of a substance which, he conceives, could possess the 

 physical properties of the original substance as a particle. 

 The particle is thus a purely conceptual notion, for we 

 cannot say when we should reach the exact limit of 

 subdivision at which the physical properties of the sub- 

 stance would cease to be. But the particle is of great 

 value in our conceptual model of the universe, for we 

 represent its motion by the motion of a geometrical 

 point. In other words, we suppose it to have solely a 

 motion of translation (pp. 198 and 205); we neglect its 

 motions of rotation and of strain. The physicist has here 

 reached a purely conceptual limit to perceptual experience ; 

 he takes a smaller and smaller element of gross " matter," 

 and supposing it always to be of the same substance 

 {i.e. to produce the same sense-impressions although it 



visible under the microscope does not contain more than about a million 

 organic molecules. Some exceedingly simple organism may be supposed 

 built up of not more than a million similar molecules. It is impossible, 

 however, to conceive so small a number sufficient to form a being furnished 

 with a whole system of specialised organs." 



This reasoning is simply a form of special pleading based on the assumption 

 that variations in physiological organs depend solely on chemical constitution 

 and not on physical structure. Why are we to put on one side the facts that 

 there are upwards of fifty atoms in the organic molecule, that there is a 

 certain proportion of water, and that these organic molecules must be 

 conceived as closely packed into a scarce visible germ ? Why are these one 

 hundred million atoms not to be conceived as physically influencing each other's 

 motion ? If this be so, then their relative position, the structure of the germ 

 as a dynamical system, may be shown to involve no less than 10,000 million 

 million periodic motions, having various relative positions in space, and apart 

 from this relative position having in amplitude, relative phase, and "note," 

 three hundred million variables at the disposal of the physiologist ! Whether 

 heredity can or cannot be described by the influence of such a molecular 

 structure on other molecules is quite beyond our present scientific knowledge 

 to determine ; but we certainly cannot dogmatically assert with Maxwell 

 that : " Molecular science sets us face to face with physiological theories. 

 It forbids the physiologist from imagining that structural details of infinitely 

 small dimensions can furnish an explanation of the infinite variety which 

 exists in the properties and functions of the most minute organisms." 



