MADE IN THE EFFICIENCY OF STEAM ENGINES IN CORNWALL, 131 
If x — 2 the friction will be 18. 
3 the friction will be 15. 
If the wheels be so arranged that the resultant of the two forces on the 
axes equal the larger in magnitude, x becomes = to A, and the amount of 
j_ i_ 
friction a A x A but a A = the radix of the natural system of logarithms ; con- 
sequently the friction in this case will be e X A. 
If the points of the two wheels receiving and communicating motion are 
placed in the same right line parallel to the axes, the general expression 
A 1 
becomes x — ] ~ I T a - 1 evidently giving to x an infinite magnitude: but this 
can indicate no more in practice than the advantage of so arranging the com- 
munications of motion when it can possibly be done. 
As fly-wheels are of essential use in preserving uniform velocities, or for ac- 
cumulating power in almost all rotatory movements produced from those that 
alternate, and as the power of the centrifugal force has sometimes exceeded 
the cohesion even of iron, I shall conclude this paper with an adaptation of 
a well-known theorem to common use. 
Let r = the radius of a wheel expressed in feet. 
v = the velocity of the rim where all the weight is supposed to be 
accumulated, expressed in feet in a second. 
s = the space in feet through which a body descends in one second 
16.0899 ; log. 1.2065541. 
F = the centrifugal force. 
Then F = ^ 
Let n = the number of revolutions in a second. 
c = the periphery of the circle to diameter unity = 3.14159. 
log. 0.4971499. 
Then F = r .n 2 X 1.2268 (log. 0.0887 757). 
Consequently for an approximate value, 
The centrifugal force = the radius X number of revolutions in a second 
squared X 1.2. 
s 2 
