PROFESSOR OSBORNE REYNOLDS AND MR. J. H. SMITH ON A 
2G8 
were carried out in such a way as to find the variation of the limiting range of stress 
as the rapidity of such reversals increased. The apparatus to be described shortly 
was most convenient for such enquiry, since both the speed and the oscillatory weight 
could be easily adjusted. 
(3) Quite apart from the point mentioned in the last paragraph, the importance of 
extending the experiments to high speeds—in view of the extensive use in recent 
times of high speed machinery—is too obvious to need comment. 
Short specimens of small diameter (see fig. 4), had to be used throughout, other¬ 
wise the apparatus would have been inconveniently heavy, and for this reason any 
subsequent work on the statical strength and the elastic properties of specimens 
which had been subjected to repeated stress, could not be done. 
Method of Applying the Stress. 
A weight is supported vertically by means of the specimen to be tested, and the 
upper part of the specimen receives a periodic motion in a vertical direction by means 
of a crank and a connecting rod^ The inertia of this weight gives a tension at the 
bottom end, and a compression at the top end of the stroke, the change from tension 
to compression being gradual. The specimen and parts are guided by suitable 
bearings placed in a vertical direction. The motion was made vertical in order to 
reduce the friction of the bearings to a minimum. The stresses can be changed by 
varying the diameter of the specimen, the load, and the speed of revolution of the 
crank. In order to enable one to calculate the stresses in the specimen, the centre of 
the crank shaft must be at rest, and the crank must move with uniform angular 
velocity. These conditions are obtained when the crank shaft is driven by a constant 
turning effort, if the moving parts of the machine are balanced, and if at the 
same time the total energy of the moving parts is invariable. The apparatus 
was therefore designed to satisfy these conditions as approximately as possible 
(see pp. 270 to 272). 
The Apparatus. 
On examining the drawings (figs. 1 and 2) of the testing machine, which show the 
working parts, it will be seen to consist of a cast-iron standard having two brass 
bushed hearings in its upper part. In these bearings a shaft, 4 inches diameter at 
the front end, and 2 inches diameter at the back end, revolves, driven by a stepped 
pulley keyed to this shaft at the back part of the machine. The standard is mounted 
upon a heavy cast-iron bed-plate (weight, 14 cwts.), not shown in the drawings. 
The front end of the shaft is cranked, the crank pin being 1|- inch diameter, 
2 inches long, and throw h inch, and a connecting rod of peculiar form is coupled to 
the crank pin. One part of this connecting rod gives an oscillatory motion in a 
vertical direction to the sliding pieces directly below the crank shaft, which pieces 
