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, such 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