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 FI. 25. 

 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 

 andC'are 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, east 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 F F, which are 

 firmly screwed into the piece (7, 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 1 1. KKis 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.,) 



