240 THE GRAMMAR OF SCIENCE 



tion of space with time is essentially a mode of perception, 

 and not in itself a perception (p. 193). The more clearly 

 this is realised the better able the reader will be to 

 appreciate that the " motion of bodies " is not a reality of 

 perception, but is the conceptual manner in which we 

 represent this mode of perception and by aid of which 

 we describe changes in groups of sense-impressions ; the 

 perceptual reality is the complexity and variety of the 

 sense-impressions which crowd into the telephonic brain- 

 exchange. That the results which flow from the conceptual 

 world of geometrical motions agree so closely with our 

 perceptual experience of the outside world of phenomena 

 (p. 65) is a phase of that accordance between the percep- 

 tive and reasoning faculties upon which I have laid 

 stress in an earlier part of this volume (p. 103). 



Wherein lies the advance from Heraclitus to the 

 modern scientist ? Why was the dictum of one not 

 unjustly termed obscure, while the other claims — and 

 rightly claims — to find in the development of his dictum 

 the sole basis for our knowledge of the physical universe ? 

 The difference lies in this : Heraclitus left his flow unde- 

 scribed and unmeasured, while modern science devotes its 

 best energies to the accurate investigation and analysis of 

 each and every type of motion which can possibly be 

 used as a means of describing and resuming any sequence 

 of sense - impressions. The whole object of physical 

 science is the discovery of ideal elementary motions 

 which will enable us to describe in the simplest language 

 the widest ranges of phenomena ; it lies in the symbolisa- 

 tion of the physical universe by aid of the geometrical 

 motions of a group of geometrical forms. To do this is 

 to construct the world mechanically ; ^ but this mechanism, 

 be it noted, is a product of conception, and does not lie 

 in our perceptions themselves (p. 1 1 5). Startling as it 

 may, when first stated, appear to the reader, it is never- 

 theless true that the mind struggles in vain to clearly 

 realise the motion of anything which is neither a geo- 



1 This word is here used in the scientific sense of Kirchhoff, and not in 

 the popular sense of Mr. Gladstone : see pp. 1 14 and 1 16. 



