442 
STEPHENSON’S PATENT 
placed outside and fixed above the wheels; and the connecting rods took hold of crank 
pins outside of the wheels and fixed into them, so as to drive them directly. But 
it was found better afterwards to place the cylinders in the smoke box, where 
they were protected from the air, which cooled them very much before; and 
the machinery could then be fixed more conveniently; some engines, however, 
are still made on that construction. Engines have also been made with vertical 
cylinders, which worked cranks outside the wheels by means of bell cranks and 
connecting rods. 
Eccentrics.—Upon the cranked axle C', (Plates XC. and XCI.,) are fixed the four 
eccentrics E', E", F', F", for the purpose of working the slide valves. The construction 
of one of the eccentrics is shewn to double the scale in figs. 24 and 25, which are 
drawn to a scale of an inch 
and a half to a foot. Fig. 24 
is a side elevation of an ec 
centric, and fig. 25 a section 
through the centre of it. A 
is a portion of the cranked 
axle,five inches diameter; B 
and Care two cast iron pieces, 
two inches and a quarter 
wide, forming the eccentric, 
and each fitted half round 
the axle; the smaller one, C, 
being one inch thick in the middle, and the two pieces forming together a circle of ten 
inches diameter. They have a projection of a quarter of an inch running round both 
sides of the outer edge, and the piece B has two openings, D D, cast in it to diminish 
the metal, leaving a thickness of an inch on each side. A rebate, E, projects from the 
straight edge of the piece C, fitting’into a groove in B to hold them steadily on each 
other; and the two pieces B and C are fixed together by the pins EE, which are 
firmly screwed into the piece C, and passing through corresponding holes in the other 
piece into the openings D D, are fixed by keys driven through them ; the whole eccen 
tric is then fixed upon the axle, so as to make them turn round together by driving the 
key G into a groove in both. The brass ring H H, one inch thick in the middle, is put 
in the groove round the eccentric; being made in two pieces in order to enable it to be 
put into the groove, and the ends connected by flanches II. K K is the eccentric rod, 
forked at the end; the ends of the fork being three-quarter inch screws, which pass 
through the flanches of the brass rings H, and hold them together by nuts upon the 
screws. The other ends of the eccentric rods e" e" and (Plates XC. and XCI.,) 
Fig. 25. Fig. 24. 
I