Sullivan on the Revolving Engine. 108 
(equally) into two forces; the one parallel to the position 
of the pitman, which of course is entirely lost, being em- 
ployed in fruitless endeavours to remove the centre piece.” 
en two forces meet at an angle, they produce a third, 
nearly equal to both in the diagonal of a parallelogram, pro- 
duced from the two lines of their direction—and yet scarcely 
pa is lost. eM 
e know too from the highest authority, “ that if any 
body draws or presses another, it is itself as much drawn or 
ressed :” that “all forces act reciprocally,” that ‘ action 
and reaction are equal”—but it is not thence concluded in 
theory—and surely it would be contrary to practice to say, 
that any of the forceis lost. 
When a boat is moved by oars, the force exerted on the 
extremity of the oar, reacts upon the boat.— 
When a lever is applied to raise a weight, the whole force 
reacts from the fulerum.— : eves 
hen a gun is fired, the elastic air acts on the bottom 
and sides of the chamber, which do not consume the force, 
but react upon the ball. 
And in like manner the force derived from the steam (in 
this case) is returned from the fixed centre piece, as a basis, 
and through the intervention of the pitman gives revolution 
to the engine. 
An unqualified objection is made to this engine, on the 
score of friction. It is said, “ the friction of this engine 
will appear evident to the most superficial observer, to be 
immensely greater than in the old engine.” 
‘This manner of expression and of judgment appears to 
be equally unphilosophical. It supposes the friction of a 
machine greater, as it may seem to such an observer com- 
icate. It seems to leave out of the question the estab- 
ished law of mechanics, that “ friction is simply propor- 
tional to the weight or pressure, that brings the substances 
concerned into contact, independently of the magnitude of 
their forces,—and that friction is a uniformly retarding 
force.” 
On these principles an engine of equal power, that is not 
more than a third as heavy as others, must have the advan- 
tage of this difference in point of friction, the work and ad- 
justment being equally perfect. It cannot be denied that « 
good adaptation of parts, makes a great difference mm ma- 
