THROW-TESTING MACHINE FOR REVERSALS OF MEAN STRESS. 
271 
(fig. 2), 8|- inches diameter, ’7 inch thick, and throw 1^ inches, and was keyed to 
the shaft as near as possible to the crank pin. 
This arrangement introduces an unbalanced couple in a plane passing through the 
centre line of the crank shaft and rotating with the shaft, and to balance this couple 
a smaller eccentric d (fig. 2) of diameter 5ir inches, thickness ^ inch, and throw 1 inch 
was placed near to the far end of the shaft with its centre in the axial plane passing- 
through the crank pin. 
So far then—neglecting the obliquity of the connecting rods, which were respec¬ 
tively 24 and 18 times the throw of the crank—the unloaded machine was balanced, 
and the kinetic energy of the parts was constant. 
FIRST POSITION SECOND POSITION 
In loading the machine the system of weights used was so designed that when 
one cast-iron weight of 6|- pounds was added to each of the oscillating pieces 
(U, Y, fig. 2), and one semicircular yg-inch steel plate was added to each side of each 
eccentric balance weight (D and d ) the machine was still balanced. It was necessary 
to use the two balance weights to each eccentric (one on each side) in order to keep 
the plane of the unbalanced force due to each pair in a constant position, that is, in 
the central plane of the eccentric perpendicular to the shaft. Fig. 2 shows the 
working parts of the machine fully loaded. 
To prevent any vibration from being transmitted to the building when the machine 
was running unbalanced, and to hold the machine in position, the bed-plate was 
supported by four spiral springs (made of y-inch steel of square section), 3 inches 
