166 
PROFESSOR OSBORNE REYNOLDS ON ROLLIN Gr-ERICTION. 
is squeezed out is amply proved by the fact that when a block of iron, hot or cold, is 
squeezed on an anvil the iron bulges out in the middle, as shown in fig. 4. 
Experimental Verification of the Figures. 
The figures which illustrate the foregoing remarks are not altogether ideal, for they 
have been verified to a certain extent by experiments on india-rubber ; for instance, by 
drawing vertical lines on the edge of a plate of india-rubber, and then observing these 
lines as the roller passed along as near as possible to this edge ; also by observing lines 
drawn in the same way on the edge of an india-rubber roller. The effect of friction to 
prevent expansion, shown in figures 4 and 5, was verified by marking the surface of the 
india-rubber under the plate A B with parallel lines in chalk, which left a mark on the 
iron and showed how far there had been slipping. The figures are nevertheless intended 
rather to illustrate the nature of the slipping and various effects than their extent, 
which latter must be judged of by the experimental results which I now proceed to 
describe. 
The Experiments. 
My first object in making these experiments was to ascertain if, and how, oiling the 
surfaces in contact affected the resistance to rolling. 
The apparatus employed consisted of a wooden slab or table-top supported on three 
set-screws for legs, so that it could be tipped in any required direction. On this table 
rested one of Whitworth’s surface-plates. On the surface-plate was placed a surveyor’s 
level, which read divisions to the thousandth of a foot on a staff erected at 50-feet 
distance ; also a bell-glass covered another part of the surface-plate in the manner of the 
receiver of an air-pump, which could be filled with oil from an aperture in the top. 
This glass served either to protect the roller from dust or surround it with oil, and thus 
prevent any surface-tension the oil might exert affecting the results. 
The roller was of cast iron, 6 inches in diameter and 2 inches thick, and weighed 
about 14 lbs. It was not cylindrical, for the edge was somewhat rounded. Originally 
the roller was turned up so that the edge was curved to a radius of 1 foot ; but subse- 
quent grinding somewhat modified this shape. 
In the first instance the roller was turned up and polished in the ordinary manner ; 
but some preliminary experiments showed that the surface thus formed was far from 
perfect, as indeed was apparent when it was examined with a magnifying-glass. The 
roller was therefore again turned and ground very carefully with Turkey-stone for 
several days, until the surface appeared through the glass to be as perfect as the iron 
would allow ; there were still some small pits, but these appeared to be in the iron 
itself. 
The roller when thus finished was rolled on various surfaces. First of all it was tried 
on the cast-iron surface-plate already mentioned ; but this surface, which had been 
formed by scraping, was altogether too rough. Thus when the roller was placed on 
the plate it immediately rolled into a hollow. Surfaces were then formed by grinding 
