[509] 
XIV. On Friction between Surfaces moving at Low Speeds. By Fleeming Jenkin, 
F.B.SS.L. & F., Professor of Fngineering in the University of Edinburgh, and 
J. A. Ewing. 
Received March 8, — Read April 19, 1877. 
[Plate 20.] 
The following paper contains an account of an investigation of the Friction between 
surfaces in motion under circumstances such as do not appear to have been examined 
before. 
The general subject of Friction has received the attention of many writers, beginning 
with Amontons in 1699. In 1799 Coulomb began to investigate it, and in 1781 he 
communicated to the Academy of Sciences a paper containing the result of his experi- 
ments, entitled “ Memoire sur la theorie des machines simples,” which is published 
in vol. x. of the ‘ Savans Etrangers.’ Coulomb pointed out the necessity of distin- 
guishing between the friction which resists the relative movement of surfaces already 
in motion, or what is now called kinetic friction, and the friction which tends to prevent 
surfaces at rest from being set in motion, or what is now called static friction. He 
found that with two dry metallic surfaces there was no difference between the static 
and kinetic friction. In the other cases which he examined there was a more or less 
considerable difference, the static being always greater than the kinetic. He found also 
that the static friction depended on the length of time during which the surfaces were 
at rest ; a prolongation of the time of rest had the effect of increasing the friction, and 
the rate of this increase varied much in different cases. When the intensity of pressure 
was great the static friction reached its highest value in a shorter time than when the 
pressure w T as small. Coulomb also examined the influence of velocity on the kinetic 
friction ; but his means of observing this seem to have been somewhat rough. He was, 
however, able to point out that generally, although subject to several exceptions, friction 
is independent of the extent of surface in contact, directly proportional to the pressure, 
and independent of the velocity. 
In 1784 Vince laid before the Royal Society the results of some experiments, which, 
although not very conclusive, agreed in the main with those of Coulomb. 
The Philosophical Transactions for 1829 contain a paper on friction by G. Rennie, 
in which an interesting account is given of the early history of the subject. Rennie’s 
experiments with hard surfaces such as those of metal or wood confirmed, as far as they 
went, the conclusions of Coulomb. 
4 c 
MDCCCLXXVII. 
