438 



STEPHENSON'S PATENT 



FIG. 22. 



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 

 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 Ibs. per 

 square inch. And as the cylinder and cranked 

 axle are firmly connected together by the frame- Flo . 23 _ 



work of the engine, they cannot be separated 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. 



