354 Professor Osborne Reynolds [Feb. 12, 



WEEKLY EVENING MEETING, 

 Friday, February 12, 1886. 



The Eight Hon. Lord Eayleigh, M.A. D.C.L. LL.D. F.E.S. Manager 

 and Vice-President, in the Chair. 



Professor Osborne Eetnolds, M.A. F.E.S. 



Experiments shoioing Dilatancy, a property of Granular Material, 

 possibly connected icith Gravitation. 



In commencing this discourse, the author said, My principal object to- 

 night is to show you certain experiments which I have ventured to 

 think wouhl interest you on account of their novelty, and of their 

 paradoxical character. It is not, however, solely or chiefly on account 

 of their being curious that I venture to call your attention to them. 

 Let them have been never so striking, you would not have been 

 troubled with them had it not been that they afford evidence of a fact 

 of real importance in mechanical philosophy. 



This newly recognised property of granular masses which I have 

 called dilatancy will, it may be hoped, be rendered intelligible by 

 the experiments, but it was not by these experiments that it was 

 discovered. 



This discovery, if I may so call it, was the result of an attempt to 

 conceive the mechanical properties a medium must possess in order 

 that it might fulfil the functions of an all-pervading aether — not only 

 in transmitting waves of light, and refusing to transmit waves like 

 those of sound, but in causing the force of gravitation between distant 

 bodies, and actions of cohesion, elasticity, and friction between adjacent 

 molecules, together with the electric and magnetic properties of 

 matte r, and at the same time allowing the free motion of bodies. 



It will be well known to those who attend the lectures in this 

 room, that although a vast increase has been achieved in knowledge of 

 the actions called the physical properties of matter, we have as yet 

 no satisfactory explanation as to the prima causa of these actions them- 

 selves ; that to explain the transmission of light and heat it has been 

 found necessary to assume space filled with material possessing the 

 properties of an elastic jelly, the existence of which, though it 

 accounts for the transmission of ligbt, has hitherto seemed inconsistent 

 with the free motion of matter, and failed to afford the slightest 

 reason for the gravitation, cohesion, and other physical properties of 

 matter. To explain these, other forms of nsther have been invented, 

 as in the corpuscular theory and the celebrated hypothesis of La Sage, 

 the impossibilities of which hypotheses have been finally proved by 



