SOi Mr Ward^s Alternating Steam-Engine. 
right angles, and extend within the wheel, and towards its cir^ 
cumference, a distance equal to half the sweep of the piston-rod 
a. At this distance from the centre of the water-wheel, boxes 
are inserted in the centre-pieces as at jf, to receive the gudgeons 
g, of the cylinder, which revolves upon them round its centre 
of gravity. The steam is conducted to and from the cylinder 
by means of a double pipe, so that the centre-pieces ai f answer 
the quadruple purpose of an induction tube and eduction tube, 
a bearing for the water-wheel, and a bearing for the cylinder. 
The steam is admitted alternately into each end of the cylinder, 
by a contrivance similar to that used by Hornblower. The 
outer end of the piston-rod «, is attached to a cross-piece 
which is supported by gudgeons g^ moveable in boxes in the 
arms rr of the water-wheel. From the middle of R proceeds 
the two wings s s, from the ends of which two rods 1 1 extend, 
playing through steps uu on the sides of the cylinder. These 
rods are considered necessary, in order alternately to overcome 
the inertia^ and resist the momentum of the cylinder, encounter- 
ed in consequence of the irregularity of its motion. 
The following is the mode in which the engine operates. The 
steam being admitted into the cylinder, by means of the induc- 
tion-tube, the beginning and end of which is shewn at i and 
elevates the piston, and consequently the piston-rod a, which 
presses the gudgeons g^ as it were against the circumference 
of the wheel, and in the direction of a tangent of a circle 
passing through the point of re-action and having for its 
centre that of the water-wheel. The upward stroke of the pis- 
ton being performed, the piston with its rod a descends, and 
the cross-piece p along mth it, the gudgeons g of the latter 
sliding in the arms rr. During the descent of the piston, the re- 
volution of the cylinder is obviously retarded, but it is again 
accelerated when the piston takes its upward stroke. From 
this regular alternate acceleration and retardation in the motion 
of the cylinder, Mr Ward has given his engine the name of the 
Alternating Steam-Engine. A full account of this machine will 
be found in the American Journal of Science^ vol. iv. p. 90, — > 
103. 
