276 Remarks on the Central Forces of Bodies 
that through which the centripetal force alone, acting uniformly, 
would cause the body to fall in the fiftieth part of a second; the 
' tangent, therefore, represents THE LINE FROM wuHicH the body 
would be deflected in an instant of time, and nor that in the di- 
rection of which tt would move with all its projectile force. 
Again, if the segment of a fly-wheel disintegrated by centrifu- 
gal force would be projected “in a straight line, whose direction 
is that of the tangent,” the pressure which produces the fracture 
must act upon each particle of iron in the direction of a tangent 
to the circle in which the particle is revolved, for the direction of 
a moving body is always that in which a single force, or the re~ 
sultant of two or more forces, acts to cause the motion... And it 
is self-evident that no amount of force, applied in that direction 
upon the particles in the revolving rim, could overcome the at- 
traction of cohesion. And it is equally evident that such cannot 
be the direction in which the pressure acts, for whilst it is stated 
that the tangent is the direction in which the dissevered fragment 
is projected, we are informed that the force which causes the 
fracture acts at right angles to the tangent. . 
By the theory given above, however, which is founded upon 
observation and experiment, all the circumstances that attend this 
phenomenon are easily explained. And when we consider the 
immense increase of centrifugal force as the velocity of the rim 
is increased, and the direction in which the resultant of the two 
Sorces acts, we ought not to be surprised to find that such masses 
of iron can be broken and projected with so much destructive ef- 
fect by this powerful agent. The operation of the sling may 
also, in this way, be explained in a few words. For aman, with 
a thong three and a half feet long, has only to give to a stove at 
the final effort a velocity, ina very small segment of a circle, 
equal to 132 feet per second, which would be at the rate of 360 
revolutions in a minute, and he will project it with a force equal 
to that given to a ball of the same weight by an ordinary charge 
of gunpowder, after deducting one third of its initial velocity for 
atmospheric resistance. But to “accumulate” an equal foree 19 
the circle by the strength of his arm, he would have to revolve 
Ho oa the rate of 6850 revolutions ina minute, which 1s 
3 Without intending to enter into any particulars as to the proba 
ble results of a practical application of this principle, I will close 
