44 SCIENTIFIC THOUGHT. 



ledge of the mechanism of the ether on the one side, of 

 ponderable matter on the other. Two ways are open by 

 which a solution of this ultimate or fundamental problem 



28. can be solved. The one is purely mathematical. It 



The problem 



of the ether meaus the analysis of all the possible modes of motion of 



may be ^ x 



mlthe** a given mechanical system, and of the mutual iniiuence 

 niaticaiiy, ^j-j^gj-^ ^-^q interconnected mechanical systems, that of the 

 ether and that of ponderable matter, exert on each other. 

 This is a perfectly definite though a very intricate prob- 

 lem. It is a problem which can be compared with — 

 though it transcends in complexity — the analytical prob- 

 lem suggested by the gravitational view of physical 

 astronomy : to calculate mathematically the movements 

 of any number of bodies attracting each other according 



29. to Newton's formula. The other way is the experi- 



or experi- 

 mentally, mental method — to observe how under methodically 



altered conditions rays of light are modified in colour 

 (wave-frequency), in direction, in intensity (amplitude of 

 wave-motion), in laterality (polarisation), and in other 

 ways ; and then to translate these conditions and altera- 

 tions into the now fairly well-established language of 

 the vibratory theory ; gaining in this way indications as 

 to the changes which the wave-motion is capable of, and 

 inferring from these possible changes the original con- 

 stitution (usvially called the constants) of the primary 

 substances — the ether and the ponderable matter which 

 come into interaction. 



30. It may in general be stated that neither of these two 



Necessity of . 



combining mcthods has for any length of time been pursued alone, 



the two J >=> f ' 



methods. ij^^ ^j^^^ progrcss lias nearly always depended upon an 

 alternating employment or a combination of both. On 



