222 APPENDIX. 



69-02)2609-425 (37'81 

 20706 



53882 

 48314 



55685 

 55216 



4690 



Beam 51*81 

 Subtract 37'81 



14'00 connecting bar from centre of beam. 



True radius of beam 64 Hor. dist. of centres 20-08 

 14 14 



Parallel bar 50 inches. Radius bar 6-08 inches. 

 These results exactly correspond with the original data. 



Note 1. For marine engines, the distance from the beam at which the radius bar is con- 

 nected, is the perpendicular height of the centre of the radius bar above the axis of the beam 

 when horizontal ; and the distance at which the piston rod is connected is the perpendicular 

 height of the cross head above the axis of the beam at half stroke, and may be found by 

 taking the height of the lowest position of the cross head, and increasing it by half the length 

 of the stroke. 



Also, the length of the connecting rod which works the crank is the perpendicular distance 

 between the centre of the shaft and the centre of the beam. 



Note 2. Calculations of parallel motions will be rather more accurate if the length of stroke 

 be diminished by its one-sixth part, before it is used ; and in fitting them they should be 

 adjusted at one-sixth of the half stroke from each end, instead of the top and bottom of the 

 stroke. 



PRESSURE ON THE PISTON. 



23. To find the mean pressure of the steam on the piston when it is worked expansively. 



RULE. Divide the length of the stroke by the distance the piston moves before the steam 

 is shut off, and the quotient will express the relative expansion it undergoes. With this 

 number take out the multiplier from the annexed table, and multiply it into the full pressure 

 per square inch of the steam on entering the cylinder. The product will be the mean pressure 

 per inch, or that pressure which, continued uniformly throughout the whole length of the 

 stroke, would produce the same effect. (155.) 



