161 
Regulating the Movements of Steam-Vessels. 
only one of which can be properly seen ; the foot of the one 
farthest from the eye is seen at the rocking-shaft. One of these 
rods lifts the upper steam-valve and lower eduction-valve ; and 
the other the lower steam- valve and upper eduction-valve. The 
lower steam- valve and upper eduction-valve are represented as 
lifted in the sketch. 
The rocking-shaft K turns and returns upon its centre 
about 40°, and having two spanners (or pallets) L, projecting 
from it upon opposite sides, cause the lifter-rods and the valves 
connected with them to rise alternately. — The lifter-rods fall by 
their own weight, and when the pallets are horizontal, all the 
valves are shut, and for an instant of time are at rest. 
The rocking-shaft receives its motion from an eccentric-wheel 
M, fastened on the crank-shaft. The fixing of this wheel with 
relation to the crank and valves, is a point of considerable nicety, 
as upon this depends the opening and shutting of the valves at 
the proper time. 
The eccentric-rod N, is supported on the crank-shaft by a 
projecting part on each side of the eccentric- wheel, turned con- 
centric with the shaft by the brass pieces O. The four rods P, 
pass through these brass pieces, and slide freely in them. This 
part is shown in the section at Pig. 2., with part of the crank (or 
paddle) shaft, and the crank on one end. The other end of the 
eccentric-rod is supported on the roller Q ; and as the crank- 
shaft turns round, the eccentric-rod travels backwards and for- 
wards a distance equal double the eccentricity of the eccentric- 
wheel, and as the said rod is connected with the rocking- shaft 
by the double-ended spanner HR on one end of it, conse- 
quently the rocking-shaft will travel from one extremity of its 
arch of motion to the other, in the same time that the crank- 
shaft makes half a revolution, or in the same time that the steam- 
piston travels from the top to the bottom of the cylinder, or 
from the bottom to the top. The steam-piston is represented 
in the middle of the cylinder, and as the lower steam-valve and 
upper eduction-valve are open, the piston must be ascending, 
. and as the crank is connected with the opposite end of the walk- 
ing-beam (or lever), the crank will be descending. By the time 
that the piston has reached the top, and the crank the bottom, 
the rocking-shaft will be in that position where the pallets upon 
VOL. XIII. "NO. 25. JULY 1825. 
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