[ 800 ] 



LXXXVII. The Relativity of Field and Matter. By Prof. 

 A. S. Edmngton, M. A., F.R.S., Plumian Professor of 

 Astronomy in the University of Cambridge*. 



THE laws of the electrical and gravitational fields, 

 expressed by Maxwell's and Einstein's equations, 

 form a remarkably complete and coherent system ; and 

 we may regard our present knowledge of field-structure 

 with considerable satisfaction. But in regard to matter 

 there is an initial difficulty not yet surmounted : we have 

 no knowledge of the laws by which the charge forming 

 an electron or proton is bound together. Thus our study 

 of world-structure seems to fall into two clear-cut divisions; 

 we distinguish — 



(1) The field, a region of which we appear to have 



sufficient knowledge. 



(2) Matter, a region of ignorance. 



In the case of matter we can, however, stride over the 

 initial difficulty to some extent by using broad principles, 

 e. g. principles of symmetry, of dimensions, or of statistical 

 averages, which do not presuppose any precise theory of its 

 structure. 



But when we examine our knowledge more minutely it is 

 scarcely possible to maintain this sharp division into field-laws 

 and material-laws ; for it contradicts the fundamental idea 

 of relativity. All our knowledge of the field is derived 

 from observations made with material appliances ; therefore 

 it cannot be knowledge of the field as an entity in itself, but 

 must be a knowledge of the relations of the field-entity to 

 matter. 



Since there is some danger of confusion of nomenclature, 

 I shall call the world-structure existing everywhere between 

 the material particles the field-entity. Then the field a& 

 studied in physics is a relation of the field-entity to matter — 

 i. <?., to the material appliances used in observing it. The 

 laws of the field are laws of this relation and belong no 

 more to one end of the relation than to the other; they are 

 just as much laws of matter as of the field-entity. 



I wish to show here that one of the principal laws of the 

 •field — Einstein's law of gravitation — becomes much more 

 elementary when regarded from the material end of the 

 relation than from the field-entity end. Regarded as a 

 property of the field-entity (relative to matter) it^appears- 



* Communicated by the Author. 



