448 STEPHENSON'S PATENT 



to have some travel, in order that the port may be full open for some time ; and 

 after having fully uncovered the port, the slides move or travel a little farther, not 

 beginning to close the port again until they have returned over the travel. The 

 motion is very varying as the eccentric drives the slide most quickly at the middle 

 of its stroke ; corresponding to the ends of the strokes of the piston, where the 

 quickest motion is wanted, to admit the steam for the next stroke ; the velocity of 

 the slide diminishing rapidly towards the ends of its stroke, where it stops and 

 retrogrades. Many contrivances have been tried in stationary engines for working 

 the slides more suddenly, either by striking the spindle with tappets or projections 

 on a moving rod, or by means of different kinds of cams or eccentrics of irregular 

 shapes ; with these plans travel of the slide would not be necessary, the port 

 being full open nearly all the stroke. But in a locomotive no plan can well be 

 adopted for working the slides which has a more Sudden or irregular motion than 

 an eccentric, because of the very great rapidity with which the strokes have to be 

 made ; which would soon cause the machinery to be deranged. 



The piston and slides make two reciprocations or changes of motion during one 

 revolution of the driving wheels, and as these are five feet in diameter, they make 

 nearly 4 reciprocations per second when the engine is running at the rate of 20 

 miles an hour, and 8 reciprocations in a second when running at a little more than 

 40 miles an hour ; the ordinary rate of working is about five reciprocations per second. 

 This extreme rapidity causes every change of motion to produce a violent blow to 

 the machinery, requiring that all the parts should be very well made and fitted to- 

 gether, in order that they may stand the work ; the greatest strain is produced upon 

 the fixing of the piston rod into the piston, and upon the joints of the piston rod 

 and connecting rod. The brasses in the crank end of the connecting rod are 

 not keyed up quite tight, but a very little play is left, allowing them just to shake 

 when worked backwards and forwards ; in order to prevent their heating by the 

 great rapidity of the motion, and expanding by the heat together with the crank 

 pin, making the joint very tight ; they have sometimes expanded so much from the 

 heating in consequence of being keyed too tight, that the engine has been nearly 

 stopped by the great friction occasioned, and the brasses have been broken to 

 pieces. 



All the moving parts require a constant supply of oil to diminish the friction ; and 

 oil cups are fixed for this purpose upon all the principal moving parts, stich as on - 

 the ends of the connecting rods over the bearings, on each of the piston rod 

 -guides, and over the piston rod and the slide valve spindle ; the piston is oiled 

 by pouring oil into the cylinder by the cock in the cylinder cover, the bent end of 



