448 The Theory of Aether a?id Electrons in the 



location at a definite moment ; the whole constituting a four- 

 dimensional world of space and time. To construct a set of 

 axes of space and time is equivalent to projecting this four- 

 dimensional world into a three-dimensional world of space and 

 a one-dimensional world of time ; and this projection may be 

 performed in an infinite number of ways, each of which is 

 distinguished from the others only by characteristics merely 

 arbitrary and accidental.* 



In order to represent natural phenomena without introducing 

 this contingent element, it would be necessary to abandon the 

 customary three-dimensional system of coordinates, and to 

 operate in four dimensions. Analysis of this kind has been 

 devised, and has been applied to the theory of the aether ; 

 but its development belongs to the twentieth century, and 

 consequently falls outside the scope of the present work. 



From what has been said, it will be evident that, in the 

 closing years of the nineteenth century, electrical investigation 

 was chiefly concerned with systems in motion. The theory of 

 electrons was, however, applied with success in other directions, 

 and notably to the explanation of a new experimental discovery. 



The last recorded observation of Faradayf was an attempt 

 to detect changes in the period, or in the state of polarization, 

 of the light emitted by a sodium flame, when the flame was 

 placed in a strong magnetic field. No result was obtained; 

 but the conviction that an effect of this nature remained to be 

 discovered was felt by many of his successors. TaitJ examined 

 the influence of a magnetic field on the selective absorption of 

 light ; impelled thereto, as he explained, by theoretical considera- 

 tions. For from the phenomenon of magnetic rotation it may be 

 inferred that rays circularly polarized in opposite senses are 

 propagated with different velocities in the magnetized medium ; 

 and therefore if only those rays are absorbed which have a 



* Cf. H. Minkowski, Raum und Zeit. : Leipzig, 1909. 

 t Bence Jones' Life of Faraday, ii, p. 449. 

 J Proc. R.S. Edinb. ix (1875), p. 118. 

 Cf. pp. 174, 216. 



