THE LUMIMFEROUS .ETHER.* 



By Sir George G, Stokes. 



I intend to bring before you to-uiglit a subject which the study of 

 light has caused me to think a good deal about: I refer to the nature 

 and properties of the so-called luminiferous iiether. This subject is, in 

 one respect, specially fascinating, scientifically considered. It lies, we 

 may say, in an especial manner on the borderland between what is 

 known and what is unknown. In the study of it, it is quite conceivable 

 that great discoveries may be made, and in fact great discoveries 

 have already been made, and I may say even quite recently, and we 

 do not at present know how much additional light on the system of 

 Nature may be in store for the men of science; jjossibly even in the 

 near future, possibly not until many generations have passed away. 

 I will assume, as what is familarly known to you all, and what is well 

 established by methods into which 1 will not enter, that the heavenly 

 bodies are at an immense distance from our earth. More especially is 

 this the case with the fixed stars. Their distance is so enormous that 

 even when we take as a base line, so to speak, the diameter of the 

 earth's oibit, which we know to be about 184:,000,000 of miles, the 

 apparent displacement of the stars due to j)arallax is so minute as 

 almost to elude our investigation. jSTevertheless that distance is more 

 or less accurately determined in the case of a few of the fixed stars. 

 But the vast majority, as we have every reason to believe, are at such 

 an enormous distance that even this method fails with them. 



To give a conception of the immense distance of the fixed stars, I 

 will assume as known that light travels at the rate of about 186,000 

 miles in one second, a rate which would carry it nearly eight times 

 round and round the earth in that time; and yet if we take the star 

 which, so far as we know, is our nearest neighbor, it Avould take about 

 four years for light from that star to reach the eartli. Now as we 

 see the fixed stars there must be some link of connection between us 

 and them in order that we should be able to perceive them. Probably 

 all of you know that two theories have been put forward as to the 

 nature of light, as to the nature accordingly of that connection of 



* Presidential address at anniversary meeting of Victoria Institute, June 29, 1893. 

 {Xatnre, July 27, 1893; vol, XLViii, pp. 306-308.) 



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