UNSOLVED PROBLEMS OF SCIENCE. 39 



entage. If they were organic beings, all our difl&cnlties 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 mask- 

 ing so many gaps in our knowledge. But the families of elemen- 

 tary atoms do not breed ; and we can not 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, can not be attributed to 

 the survival of the fittest in the struggle for existence. We can 

 not account for the minute difference which persistently distin- 

 guishes nickel from cobalt, by ascribing it to the recent inherit- 

 ance by one of them of an advantageous variation from the par- 

 ent stock. 



The upshot is that all these successive triumphs of research, 

 Dalton's, Kirchhoff's, Mendel^eff 's, greatly as they have added to 

 our store of knowledge, have gone but little way to solve the 

 problem which the elementary 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 labors, and 

 which may be said to have called chemistry into being, has as- 

 suredly not been realized, but it has not yet been refuted. The 

 boundary of our knowledge in this direction remains 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 sci- 

 ence, would be the question of what is called the ether. The ether 

 occupies a highly anomalous 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 wer.e to speak of it as a 

 body or even as a substance. When, nearly a century ago. Young 

 and Fresnel disco\f ^red that the motions of an incandescent par- 

 ticle 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 undulate." Lately, our concep- 

 tion of this entity has received a notable extension. One of the 

 most brilliant of the services which Prof. Maxwell has rendered 



