92 SIK G. GABRIEL STOKES^ BART., F.R.S.^ ON 



onr meetings ; and through the pubhcation of our Journal, 

 containing the papers read before us, with an abstract of the 

 discussions to wliich the}^ gave rise, a far wider circle is 

 reached than that of merely those who are assembled at the 

 meetin^t^'. 



I have said that I did not regard the Institute as primarily 

 a Society for scientific research, and yet (mr objects bring us 

 closely into connection with research of that kind. In what 

 way can purely scientific questions be most properly brought 

 before the Institute, considering the object for Avhich it was 

 established ? For my own part I think that one of the most 

 useful things that can be clone by those who bring forward 

 scientific matters is to present a general view of our scientific 

 knowledge on those subjects to which they themselves have 

 more particularly attended, or to expound the conclusions to 

 which some special research of their own may have conducted 

 them, when those conclusions may seem to have some bearing, 

 even though it be remote, on the other branch of our subject. 

 In pursuance of this idea, I intend to bring before you to- 

 night a subject which the study of fight has caused me to 

 think a good deal about : I refer to the nature and properties 

 of the so-called luminiferous ether. 



This subject is, in one respect, specially fascinating, 

 scientifically considered. It lies, we may say, in an especial 

 manner on the border land 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; 

 possibly even in the near future, possibly not until many 

 generations have passed away. I will assume, as what is 

 familiarly known to you all, and what is well established by 

 methods into Avhich I will not enter, that the heavenly bodies 

 are at an immense distance from our earth. ]\Iore 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 orbit, which we know to be about 

 184 millions of miles, the apparent displacement of the stars 

 due to parallax is so minute as almost to elude our investiga- 

 tion. Nevertheless 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. 



