438 
STEPHENSON’S PATENT 
for five inches in length, having a collar at the end; these parts, G G, turn in 
brasses, which are fixed in the outside frame of FlG * 22, 
the engine, and have the weight of the engine 
resting upon them. The axle is all turned in 
a lathe, and each of the crank pins is also 
turned by suspending the axle on centres cor 
responding with the centre of the crank pins; 
and made in strong cast iron arms, that are 
firmly fixed on the ends of the axle, and pro 
ject beyond the cranks, so as to balance the 
axle, and enable it to turn round on the centre 
line of the crank pin. The axle is by this means 
made very true, and the cranks are made of 
exactly the proper length, and at right angles to 
each other. The corners of the cranks are 
champered off, as shewn in the figure, and the 
ends of the smaller cylindrical parts well 
rounded out. 
The crank R of the right hand cylinder 
is shewn vertically, and in its lowest position; 
and the piston in the cylinder is shewn in the 
middle of its stroke, or at half stroke. (See 
Plate XC.) If the piston be now made to 
move backwards, by admitting the steam to 
the front of it, it will press against the crank 
pin by means of the piston rod and connecting 
rod, with a force equal to the pressure of the 
steam upon it; and as the piston is twelve inches 
diameter, or 113 square inches area, this force 
upon the crank will be 2^ tons, when the 
steam is at the usual pressure of 50 lbs. per 
square inch. And as the cylinder and cranked 
axle are firmly connected together by the frame- Fig . 2 3. 
work of the engine, they cannot be sejmrated by this force upon the crank; 
the crank therefore gives way by turning round, making the axle and wheels 
upon it revolve in the direction of the arrow, until it is brought to its farthest 
position and becomes horizontal, as the left hand cylinder is shewn in Plates XC. 
and XCI., and the piston has arrived at the end of its stroke.