104 REPORT—1843. 
Report of the Committee appointed by the British Association for 
Experiments on Steam-Engines. Members of the Committee :— 
Eaton Hopexinson, Esq., F.R.S.; J. Enys, Esg.; Rev. Pro- 
fessor Mose.ey, M.A. F.R.S.; and Professor Witu1amM Poue. 
Your Committee, in reporting the progress of the experiments entrusted to 
their care, have the pleasure of stating that they have succeeded in accom- 
plishing the principal object which has engaged their attention during the 
past year; namely, to ascertain by actual experiment the velocity of the 
piston of a single-acting Cornish pumping-engine, at all points of its stroke. 
Unfortunately, however, from delays and accidents, arising from causes in- 
herent in the delicate nature of the operations required and the machine used, 
there has not been yet time to obtain the data and work out the calculations 
necessary for comparing the results of experiment with those of theory, and 
by that means eliciting the useful information which it is hoped this com- 
parison will offer to practical science. 
The velocity-measuring machine constructed by Breguet of Paris, under 
the kindly proffered direction of M. Morin, was received a few months ago, 
It is on the same principle as those with which the beautiful experiments of 
M. Morin on friction were made, and which are described minutely in the 
works of this writer (Nouvelles Expériences sur le Frottement, or Déscrip- 
tion des Appareils Chronométriques). These may be referred to for a full 
and complete explanation of the construction and action of the machine, but 
the principle of it may be briefly explained as follows. 
A circular disc, covered with card or paper, is made to revolve with a uni- 
form motion by means of clockwork regulated by air vanes. Upon this dise, 
a revolving pencil, whose motion is caused by and corresponds with that of 
the body whose variable velocity is to be measured, describes a curved line: 
and from this curve, which results from a combination of the variable with 
the uniform motion, the velocity may be easily ascertained by processes and 
formule adapted to the purpose. 
This beautiful and ingenious contrivance, by which spaces described in 
the 10,000dth part of a second may be easily discerned, is the invention of 
M. Poncelet, carried into execution by M. Morin. 
On examining the machine, it was found necessary to make some few re- 
pairs of injuries it had received in carriage, and also some alterations to fit it 
for the particular purpose it was proposed to apply it to. These were done 
by Mr. Holtzapffel. 
The instrument, when put in order, was first tried at King’s College, a 
variable motion being given by a small carriage made to descend an inclined 
plane. The correspondence of the velocity shown by the machine, with that 
deduced by the known laws of dynamics, was such as to give great confi- 
dence in its accuracy ; and after a few minor alterations suggested by fre- 
quent trials, it was removed to the East London Water Works, Old Ford, 
and, by the kind permission of Mr. Wicksteed, the engineer, was attached to 
the Cornish engine at work there. This was considered a very favourable 
engine to experiment upon, inasmuch as the constants involved in its work- 
_ ing had been so accurately ascertained by Mr. Wicksteed in his previous ex- 
periments, and so amply confirmed by the long trial of the constant indicator 
upon it by your Committee during the years 1841 and 1842. 
After several preparatory trials and adjustments, some diagrams were taken 
on the 8th of August, and the velocities calculated from these have been ex- 
pressed in the form of geometrical curves, whose abscisse represent the 
spaces passed over by the piston of the engine, and whose ordinates indicate 
the corresponding velocities at the different points of the stroke. 
The velocity of the in-door, or descending stroke of the piston, is taken from 
the mean of three experiments, differing very little from each other. The 

