390 Anniversary Meeting. [Nov. 30, 



splendid nineteenth century "physical mathematics," invented and 

 founded by those great men ; and with a wholly original genius for 

 discovery in properties of real matter, which enhanced the superlative 

 beauty of the mathematical problems by fresh views deep into the 

 constitution of matter. 



In the purely mathematical part of his hydro-dynamical subject he 

 advanced from the " infinitely small " waves of Caucby and Poisson 

 to deep-sea waves of such considerable steepnesses and lengths and 

 heights as are seen in nature on water 500 fathoms deep, or more, 

 after a severe gale far away from land ; and he has shown how to 

 carry on his mode of solution right up to breaking waves at sea and 

 tidal bores in shallow water. 



His enunciations and solutions for motion of viscous fluids, rich 

 with applications to natural phenomena the distance of audibility 

 of sound, the suspension of clouds in the air, the subsidence of 

 ripples on a pond and of waves on the ocean after the cessation of 

 wind ; and rich in aids to scientific investigation, as in the theory of 

 the pendulum in air have added to hydro- dynamics a previously 

 unknown province, in which the exceeding difficulty of the mathe- 

 matical work deserves every capable effort to advance it, on account 

 of the vast practical and scientific importance of the issues. 



His " instability " of the motion of a viscous fluid in the neighbour- 

 hood of a solid gives the key to the scientific mystery of turbulent 

 motion in practical hydraulics, and in wind blowing over solid earth ; 

 the hearing of sounds in the direction of the wind which are inaudible 

 at equal distances in the contrary direction; the flow of water in 

 rivers, culverts, and water supply pipes; the "skin-resistance" of 

 ships, the scientific consideration of which has done so much to make 

 22 knots a proper speed for travelling by sea. 



Of true dynamical science in all these subjects Stokes' early work 

 was the beginning. It also first gave true views as to that very 

 important practical subject, the rigidity, and the resistance against 

 compression, of solids ; views which would be false if a majority of 

 votes in the scientific world of 1893 could decide between truth and 

 error. 



In optics and the undulatory theory of light, Stokes has been the 

 teacher and guide of his contemporaries. His Report to the British 

 Association in 1862, " On Double Refraction," showed with perfect 

 accuracy and clearness the outstanding difficulties, but called special 

 attention to the door which Green had opened for escape from them. 

 That Report has given the starting impulse and essential information 

 for nearly all that has been done for the subject in England since its 

 publication. 



By his own experimental and mathematical work on the polarisa- 

 tion of light by a grating, and of the light of the blue sky ; by his 



