8 EEPORT — 1894. 



shortly after the publication of his theory, were found to be duly clothed 

 with the qualities he required in each. This remarkable confirmation has left 

 MendeleefF's periodic law in an unassailable position. But it has rather 

 thickened than dissipated the mystery which hangs over the elements. 

 The discovery of these co-ordinate families dimly points to some identical 

 origin, without suggesting the method of their genesis or the nature of 

 their common parentage. If they were organic beings all our difficulties 

 would be solved by muttering the comfortable word ' evolution ' — one 

 of those indefinite words from time to time vouchsafed to humanity, 

 which have the gift of alleviating so many perplexities and masking so 

 many gups in our knowledge. But the families of elementary atoms do 

 not breed ; and we cannot therefore ascribe their ordered difference to 

 accidental variations perpetuated by heredity under the influence of 

 natural selection. The -rarity of iodine, and the abundance of its sister 

 chlorine, cannot be attributed to the survival of the fittest in the struggle 

 for existence. We cannot account for the minute difference which per- 

 sistently distinguishes nickel from cobalt, by asci'ibing it to the recent 

 inheritance l)y one of them of an advantageous variation from the parent 

 stock. 



The upshot is that all these successive triumphs of research, Dalton's, 

 Kirchhoff 's, Mendele'eff 's, greatly as they have added to our store of know- 

 ledge, have gone but little way to solve the problem which the elemen- 

 tary atoms have for centuries presented to mankind. What the atom of 

 each element is, whether it is a movement, or a thing, or a vortex, or a 

 point having inertia, whether there is any limit to its divisibility, and, if 

 so, how that limit is imposed, whether the long list of elements is final, or 

 whether any of them have any common origin, all these questions remain 

 surrounded by a darkness as profound as ever. The dream which lured 

 the alchemists to their tedious labours, and which may be said to hav& 

 called chemistry into being, has assuredly not been realised, but it has not 

 yet been refuted. The boundary of our knowledge in this direction re- 

 mains where it was many centuries ago. 



The next discussion to which I should look in order to find unsolved 

 riddles which have hitherto defied the scrutiny of science, would be the 

 question of what is called the ether. The ether occupies a highly anoma- 

 lous position in the world of science. It may be described as a half- 

 discovered entity. I dare not use any less pedantic word than entity tO' 

 designate it, for it would be a great exaggeration of our knowledge if I 

 were to speak of it as a body or even as a substance. When nearly a 

 century ago Young and Fresnel discovered that the motions of an incan- 

 descent particle were conveyed to our eyes by undulation, it followed that 

 between our eyes and the particle there must be something to undulate. 

 In order to furnish that something, the notion of the ether was conceived, 

 and for more than two generations the main, if not the only, function of 

 the word ether has been to furnish a nominative case to the verb ' to un- 

 dulate.' Lately, our conception of this entity has received a notable 



