A Fluid Analogue for the yEther. 651 



The experiments described in detail in this paper were for 

 the main part carried out in 1^14, and a short reference to 

 the results was made in "X Rays and Crystal Structure." 



I wish to express my gratitude to Dr. Hutchinson, of 

 the Mineralogical Laboratory, Cambridge, and Dr. Gordon r 

 of King's College, London, for their kindness in supplying 

 the material used, and to Mr. W. R. James, who assisted me 

 in making some of the observations. 



LXIV. A Fluid Analogue for the ^FJtJier. By Dr. G. Green,, 

 Lecturer on Natural Philosophy in the University of 

 Glasgow* '. 



THE purpose of the present paper is merely to illustrate 

 by means of an analogy certain points of resemblance 

 (especially with reference to wave-propagation) between the 

 eether and ordinary fluids, to some of which particular 

 attention has not hitherto been drawn. The conception 

 of the tether as a fluid medium has already been very 

 fully discussed! and it is known to be subject to important 

 limitations. Nevertheless it is desirable at the present time 

 that the relations of matter and aether should be examined 

 in every possible aspect, and the anaL gy now to be con- 

 sidered, th'Ugh in itself incomplete, may be of interest as 

 an illustrative system, and possibly also in its bearing upon 

 some problems of the aether still requiring solution. Recent 

 experimental observations have compelled us to modify 

 certain ideas regarding the physical characteristics to be 

 associated with the aether, in proving that the aether is 

 capable of acting as a very slightly refracting medium 

 in strong gravitational fields. This discovery has to 

 some extent suggested the line of comparison between 

 aether and ordinary matter which is followed in the present 

 paper. 



One of the main functions to be fulfilled by the aether is 

 the apparently two- fold function of conveying waves of 

 light and of electric and magnetic force at a constant 

 velocity and of propagating the forces, of gravitation. 

 There have been associated with the aether certain elastic 

 qualities enabling it to transmit transversal vibrations 

 and at the same time to transmit a stress analogous to 

 tensional stress in elastic material; and it is natural to 



* Communicated bv the Author. 



t See FitzGerald, Proc. Roy. Dublin Soc. vol. ix. (1899). 

 v U 2 



