Mr. N. Campbell on the ^Etlier. 181 



Coordinates quantities defined by 



, Ch/m , dx'm _ dy m _ dw^ « 



Xm dT~ lJm dt ~' r,n dt * Jm dt + «»>••■ ^ 



then we shall get different values of r mn . 



I must confess that the contemplation of that proposition 

 leaves me perfectly calm. The first part of it is a deduction 

 from the fact that the equations have been formulated so 

 that the Absolute Coordinates enter only as differences or as 

 differential coefficients of the second order with respect to 

 the time ; the second part of it states that they have been 

 formulated so that some other rather complicated proposition 

 is not true. The statement that the fundamental equations 

 of mechanics have one form rather than another seems to me 

 perfectly commonplace ; but it is wonderful that they have 

 any form at all : that we can formulate equations of such 

 generality. And it is no less wonderful (and no more) that 

 we can formulate Van tier Waals's equation or any other 

 equation which is the expression of a scientific theory. That 

 we can form theories which, so far as we can see at the time 

 of their formation, might be inconsistent with the next 

 observation, but are, as a matter of fact, never inconsistent 

 with any observation, is the most wonderful thing about 

 science, and raises the most interesting and difficult philoso- 

 phical problems. But these problems are raised by every 

 branch of physics and not by dynamics alone. 

 September 1900. 



XV. Hie ^Eiher, By Norman ( 'amtbell, Fellow of 

 Trinity College, Cambridge*, 



§ 1. rpHE position of the conception of "the aether" in 

 X modern physics is anomalous and unsatisfactory. 

 From the works of some writers it might appear that at no 

 period was the conception of more fundamental importance 

 or of more indisputable validity, but there are others who 

 have ceased altogether to employ the conception and regard 

 it as a hindrance to progress. And this conflict of opinion 

 is of a somewhat different nature to almost all the previous 

 disagreements which have divided men of science. The 

 question which is involved is not primarily one of the value 

 of experimental evidence, or of the main features of its 

 interpretation. No doubt much of the dissatisfaction with 

 " the aether " is based on the recent theories of the atomic 



* Communicated bv the Author. 



