300 THE GRAMMAR OF SCIENCE 



whether they come to the same position face to face, or 

 back to back, as it were ? Lastly, if we know how A and 

 B influence each other's motions when they are alone in 

 the field, and how A and C dance when alone together, 

 shall we be able to tell how A will act in the presence of 

 botli B and C ? Here are a number of ideas which we 

 must try and express in scientific language with the view 

 of determining what answers are to be given to the 

 problems they suggest. 



In the first place we ask the question : — 

 Is there any relation between the mutual accelerations 

 of two corpuscles A and B, which is independent (i) of 

 their relative position, and (2) of their possible companions 

 in the field ? Is there any relation, in fact, which depends 

 on the individualities of the corpuscles A and B ? 



This problem may be termed that of the Kinetic Scale} 

 Let us see how we might solve this problem ideally. We 

 might take two corpuscles and put them at different 

 distances in a field in which they alone exerted influence, 

 and we might measure their mutual accelerations. Then 

 we might repeat this process with other corpuscles in the 

 field," and vary the field itself in every possible manner. 

 We should thus obtain two series of numbers, the one 

 series representing the acceleration of A due to B,^ and 

 the other the acceleration of B due to A. In the sphere 

 of conception we should then be applying the scientific 

 method of classifying facts, and trying by careful examina- 

 tion of these facts to discover a law or formula by aid of 

 which they might be described. And we should very 

 soon find a fundamental relation between these mutual 

 accelerations of A and B. Returning to our Fig. 22, we 



1 Kinetic is an adjective formed from Greek KLvrjai^, a daiict, a movement ; 

 the kinetic scale signifies a scale of movement. 



2 The manner in which the part of A's acceleration due to B might be 

 separated from that due to the other corpuscles in the same field cannot be 

 fully discussed in this work. In many cases it could be discriminated by aid 

 of the parallelogram of acceleration (p. 236). 



^ By the expression "acceleration of A due to B," frequently used in this 

 chapter, the reader is not to understand that B etiforces A's change in motion. 

 The term is solely used as shorthand for the conceptual idea that A and B, 

 when in each other's presence, are to be considered as changing their relative 

 motions in a certain manner. 



