The wrong key inserted. The pins do not allow
the lock to be turned.]

* * * * *

THE CYCLE.

There are a few features of this useful and in some ways wonderful
contrivance which should be noticed. First,

THE GEARING OF A CYCLE.

To a good many people the expression "geared to 70 inches," or 65, or
80, as the case may be, conveys nothing except the fact that the higher
the gear the faster one ought to be able to travel. Let us therefore
examine the meaning of such a phrase before going farther.

The safety cycle is always "geared up"--that is, one turn of the pedals
will turn the rear wheel more than once. To get the exact ratio of
turning speed we count the teeth on the big chain-wheel, and the teeth
on the small chain-wheel attached to the hub of the rear wheel, and
divide the former by the latter. To take an example:--The teeth are 75
and 30 in number respectively; the ratio of speed therefore = 75/30 =
5/2 = 2-1/2. One turn of the pedal turns the rear wheel 2-1/2 times. The
gear of the cycle is calculated by multiplying this result by the
diameter of the rear wheel in inches. Thus a 28-inch wheel would in this
case give a gear of 2-1/2 x 28 = 70 inches.

One turn of the pedals on a machine of this gear would propel the rider
as far as if he were on a high "ordinary" with the pedals attached
directly to a wheel 70 inches in diameter. The gearing is raised or
lowered by altering the number ratio of the teeth on the two
chain-wheels. If for the 30-tooth wheel we substituted one of 25 teeth
the gearing would be--

75/25 x 28 inches = 84 inches.

A handy formula to remember is, gearing = T/_t_ x D, where T = teeth on
large chain-wheel; _t_ = teeth on small chain-wheel; and D = diameter of
driving-wheel in inches.

Two of the most important improvements recently added to the cycle
are--(1) The free wheel; (2) the change-speed gear.

THE FREE WHEEL

is a device for enabling the driving-wheel to overrun the pedals when
the rider ceases pedalling; it renders the driving-wheel "free" of the
driving gear. It is a ratchet specially suited for this kind of work.
From among the many patterns now marketed we select the Micrometer
free-wheel hub (Fig. 222), which is extremely simple. The
_ratchet-wheel_ R is attached to the hub of the driving-wheel. The small
chain-wheel (or "chain-ring," as it is often called) turns outside this,
on a number of balls running in a groove chased