THE WAVE THEORY OF LIGHT. 105 



tion in seeing all that the stud}' of light has brought of new ideas on 

 the mechanism of the forces of nature. 



It has insensibly restored the Cartesian conception of a single medium 

 refilling space, the seat of electrical, magnetic, and luminous phe- 

 nomena. It allows us to foresee that this medium is the depositary of 

 the energy spread throughout the material world, the necessary vehicle 

 of every force, the origin even of universal gravitation. 



Such is the work accomplished b}' optics. It is perhaps the greatest 

 thing of the century! 



The study of the properties of waves, viewed in every aspect, is 

 therefore, at the present moment, the most fertile study. 



It is that which has been followed in the double capacit}' of geome- 

 ter and physicist by Sir George Stokes, to whom we are about to pay 

 so touching and deserved a- homage. All his beautiful researches, both 

 in hydrodynamics as well as in tiieoretical and practical optics, i-elate 

 precisely to those transformations which various media impose on 

 waves which traverse them. 



In the many phenomena which he has discovered or analvzed, move- 

 ments of fluids, difiraction. interference, fluorescence, Rontgen ra3's, 

 the dominant idea which I pointed out to j'ou is always visible. It is 

 that which makes the harmonious unity of the scientific life of Sir 

 George Stokes. 



The University of Cambridge may be proud of the Lucasiun chair 

 of mathematical physics, because from Sir Isaac Newton up to Sir 

 George Stokes it has contributed a glorious part toward the progress 

 of natural philosophy. 



