896 REPORT—1885. 
be also a court of the Gentiles, where those whose fate or whose choice it is to 
serve science unadorned may find a modest reception. I believe that the adoption 
of this suggestion would enormously extend the usefulness of our great scientific 
societies, and give to their voice a weight which it never had before. At all 
events, if the trammels of tradition, or some better reason with which I am un- 
acquainted, should prevent them from broadening their basis in the way I indicate, 
nothing prevents the British Association, with its more liberal constitution, from 
considering what may be done for the scientific plebeian. 
There is one other function of the British Association in connection with 
which I wish to venture another suggestion. During the annual meeting, scientific 
men haye an opportunity of making each other's acquaintance. Great men ex- 
change ideas with great men; and, most important of all, young and little men 
have a chance, rarely otherwise afforded, of taking a nearer view of the great. 
What I would suggest for consideration is, whether it might not be possible to 
form an organisation which would in a certain sense carry this advantage through 
the whole year. I have already alluded more than once to the difficulties that the 
scientific public—and here I include professional men generally, in fact all but the 
leaders of science—have in keeping pace with recent advances. Would it not be 
possible to have an arrangement enabling at least every large centre of the higher 
education to haye periodically the benefit of communion with and instruction from 
the high priests of the various branches of science? How glad we, the teachers of 
science in Edinburgh for example, would be to have a course of lectures once every 
three or four years from Professors Cayley, Sylvester, Stokes, Adams, or Lord 
Rayleigh. In this way effect would be given to the principle which cannot be 
too much insisted upon, that the power of the spoken word far exceeds that of the 
written letter. Not only should we learn from the mouths of the prophets them- 
selves the highest truths of science, but the present generation would thus come to 
Imow face to face, as living men, those whose work will be the glory of their time 
and a light for future ages. From the want of a proper circulating medium, the 
influence of great scientific men very often does not develop until they and the 
secrets of their insight have gone from among us. The object of what I propose 
is to make these men more of a living power in their own lifetime. 
The following Papers were read :— 
1. On the Dilatancy of Media composed of Rigid Particles in Contact.} 
By Professor Osporne Reynoups, M.A., FBS. 
In the account which Professor Reynolds gave of his paper, he did not submit 
a complete dynamical theory, but discussed a very fundamental property of 
granular masses. To this property he gives the name of dilatancy. It is ex- 
hibited in any arrangement of particles where change of bulk is dependent upon 
change of shape. In the case of fluid matter, as we know it, change of shape and 
volume are independent. In solids they are sometimes not separable. With 
granular masses the result is different—change of shape always produces change of 
volume. And further, in every case, if change of volume is prevented all change 
of form is impossible. 
If we suppose the granular masses to be spherical, no granule can change its 
position without disturbing the adjacent particles—for the granules are all supposed 
to be perfectly rigid, and to be absolutely in contact ; and the internal particles are 
fixed if the external ones are. In illustration Professor Reynolds showed a model 
of connected spherical bodies arranged in crystalline form, This model showed the 
arrangement of the particles corresponding to, say, the condition of least possible 
density of the whole mass (about one-half the density of the separate spheres). 
The shape could then be altered to that which corresponds to maximum density— 
the change taking place by sliding of the particles one upon another. Between the 
extreme states there are intermediate stages of equilibrium corresponding to maxi- 
mum-minimum positions, where alteration in one direction produces decrease of 
density, and in the other increase of density. 
1 Published in full in Phil Wag. Dec. 1885, p. 469, 
