476 Prof. Osborne Reynolds on the Dilatancy of Media 



by the sliding of an internal layer within the mass. Hence 

 where two parts of the mass are connected by such a surface, 

 certain conditions of strain of the boundaries may be accommo- 

 dated by a continuous stream of balls adjacent to the surface. 

 This fact made itself evident in two very different experiments. 



In order to examine the formation wilich the shot went 

 through, an ordinary glass funnel was filled with shot and oil, 

 and held vertical while more shot were forced up the spout 

 of the funnel. It was expected that the shot in the funnel 

 would riee as a body, expanding laterally so as to keep the 

 funnel full. This seems to have been the effect at the com- 

 mencement of the experiment ; but after a small quantity had 

 passed up it appeared, looking at the side of the funnel, that 

 the shot were rising much too fast, for which, on looking into 

 the top of the funnel, the reason became apparent. A sheet 

 of shot adjacent to the funnel were rising steadily all round, 

 leaving the interior shot at the same level with only a slight 

 disturbance. 



In another experiment one india-rubber bag was filled with 

 sand and water ; at the centre of this ball was another much 

 smaller ball, communicating through the sides of the outer 

 envelope by means of a glass pipe with an hydraulic pump. 

 It was expected that, on expanding the interior ball by water, 

 the sand in the outer ball would dilate, expanding the outer 

 ball and drawing more water into the intervening sand. This 

 it did, but not to the extent expected. It was then observed 

 that the outer envelope, instead of expanding, generally bulged 

 in the immediate neighbourhood of the point where the glass 

 tube passed through it ; showing that this tube acted as a 

 conductor for the sand from the immediate neighbourhood of 

 the interior ball to the outer envelope, just as the glass sides 

 of the funnel had acted for the shot. 



As regards any results which may be expected to follow 

 from the recognition of this property of dilatancy, — 



In a practical point of view, it will place the theory of earth- 

 pressures on a true foundation. But inasmuch as the present 

 theory is founded on the angle of repose, which is certainly 

 not altered by the recognition of dilatancy, its effect will be 

 mainly to show the real reason for the angle of repose. 



The greatest results are likely to follow in philosophy, and 

 it was with a view to these results that the investigation was 

 undertaken. 



The recognition of this property of dilatancy places a 

 hitherto unrecognized mechanical contrivance at the com- 

 mand of those who would explain the fundamental arrange- 

 ment of the universe, and one which, so far as I have been 



