TRANSACTIONS OF THE SECTIONS. 121 
the contrary will, however, be evident to any one who takes the trouble to make the 
necessary calculations. The relative size of the weights diminishes as the engine 
becomes large. 
Since the whole engine acts as a fly, we require no fly-wheel, and there is no 
temptation to make any portion weak; since the heavier and stronger it is, the 
greater its power. Its entire weight may be less than that of the fly-wheel of an 
ordinary engine of the same power, and it will not occupy more space than would 
_be required for the fly-wheel only. 
It might be thought that such large masses, at one side of the centre of motion, 
must necessarily cause great strain and vibration. But I beg to call attention to 
the important difference there is between the uncounterbalanced masses being moved 
by the power, and being themselves the power. If they are moved by the power they 
will cause a very great strain and vibration, as might be illustrated by fixing even a 
small fraction of them to a wheel having the same diameter as the circle, in which 
their centre gravity revolves when they are attached to the engine.—We soon found 
it necessary to counterbalance the cylinder, &c. by the counterpoise D H, which 
at the same time, serves also as a strong and convenient support, along with the 
cylinder, for the guide-bars F,F. On the other hand, the weights themselves, 
however great, being the medium through which the force is transmitted, require no’ 
counterpoise. 
Since the steam is used very expansively, the upward motion of the weights is 
gradually retarded, and any small quantity of it, which remaining would cause con- 
cussion or vibration, is destroyed by a portion of the waste steam. There is not, 
however, any obstacle offered to the exit of the latter, which has, at least, as great 
facility for escape as in the ordinary engine; and whatever quantity of it acts as a 
cushion, is so much towards the filling of the cylinder at the next stroke. 
We do not require a governor, since the engine contains within itself more than 
One principle of self-regulation, which prevents its speed being sensibly altered, even 
with extreme variations of resistance. 
It might be supposed that we lose power by centrifugal force, but this is not the 
case, since whatever extra force may be necessary, on account of it, during one part 
of the stroke, is given out during the other. It affords us one principle of self-regula- 
tion ; for if the engine even slightly exceeds the proper speed, the increased centrifugal 
force causes the weights to be projected upwards with increased velocity ; but the 
__ waste not having then sufficient time to escape, the stroke is shortened, and by con- 
sequence the velocity is diminished. A little consideration will show that the con- 
samption of steam is exactly proportioned to the length of stroke, and therefore to 
_the power of the engine. 
I may take this opportunity of remarking, that the rotary motion is another 
source of self-regulation; for it not only, by means of a fixed excentric, opens the 
ports at the proper time after their having been closed by the upward motion of the 
weights, but also, by cutting off the steam more rapidly, and diminishing the velo- 
_ city with which the waste escapes, shortens the stroke, and thus reduces the speed 
of revolution. 
The slide-valve has fwo motions quite independent of each other, and yet the con- 
_trivances by which they are effected are, to a certain degree, connected together. The 
fixed excentric opens the ports exactly at the proper time, whenever that may be; 
and the upward motion of the weights, in whatever position raised, closes them to 
_ the required extent. These movements, though, as is perceived by the model, so 
_ simple and effective, are the result of long and troublesome experiments. ’ 
The overrunning of the piston at high velocities, was, at first, one of our great dif- 
ficulties, but it is now highly advantageous to us. The piston, at high velocities, 
_ moves so rapidly, that the steam, not having time to follow it, is used still more ex- 
_ pansively than in other circumstances. ™, ee 
1 The weights are, no doubt, falling bodies, but our velocity is not on that account 
limited, since they are in reality bodies which continually fall, and therefore have 
__ their velocity increased till it reaches a maximum, dependent on circumstances. 
_ The portions of the weights which are at one side of the’centre of motion do not 
| counterbalance those at the other.—The common centre of gravity of the recipro- 
| cating masses is lifted through a distance equal to the stroke, and before it can be 







