Revolving about Fived Ares. 271 
ed to an arm revolving in a circle of eight feet in diameter, and 
let EF be an arch of that circle, touching the straight line Ag at 
B. As the velocity of the bar and the circumference of the circle 
are equal, the bar, after being attracted by the magnet at B, would 
move on with the same uniform velocity and perform one entire 
revolution in a second, friction and the resistance of the atmos- 
phere being considered equal to nothing. 7 its deflection from 
the straight line, or its centripetal force for =', of a second, would 
be equal to the square of the arch Bz, whith’ is six ‘Richens divi- 
ded by the diameter of the circle, that sae 375 = % of an 
inch, or only one eighth of the deflection caused by the smaller 
wheel; and in the same ratio for any other spaces through which 
the bar would have passed whilst moving through equal spaces 
in the circle. And hence it is that the central forces are inversely 
as the diameters of the circles in which a body is made to move 
with a given velocity. sae increment of deflection for an en- 
: 25.14 
tire second being = “= 632 feet per second in the ae 
: 25.14? 
wheel, and in the larger one= a, 2 feet per second eae 
and yet the bar has precisely the same velocity; and consequently 
the same force in the latter that it had in the former. Therefore, 
aside from friction, it would, if welded to m, require no more 
force to revolve it in the former than in the latter case. 
For the same reasons, “with a given velocity for the particles 
of the rims, the smaller a fly-wheel is, the greater will be the 
amount of centrifugal force, other things being equal. This-will 
appear obvious upon inspecting the figure ; for it will be seen that 
a particle of iron at v in the rim of a small wheel would be de- 
flected from the straight line eight times as many inches in a given 
unit of time asa particle would be at the point z of the large wheel. 
The measure of the deflection from that line must therefore be 
the measure of the centrifugal force for any instant of time; and 
consequently the aggregate amount will be proportionate to the 
curve in which the body moves. This deflection takes place 
when a body is moved in a curved line, and the tendency to resist 
it and move in a straight line is excited in such a mass of matter 
in obedience to the important law of inertia, with as much cer- 
tainty as electricity would result from the action of sulphuric 
