Some of the objections to the bicycle to which I have referred were
sufficient to prevent many, especially elderly men, from dreaming of
becoming cyclists. So long as the tricycle was a crude and clumsy
machine, there was no chance of cycling becoming a part, as it almost is
and certainly soon will be, of our national life. The tricycle has been
brought to such a state of perfection that it is difficult to imagine
where further progress can be made.

Perhaps it will be well to mention what is necessary in order that a
three-wheeled machine may be made to roll freely in a straight line, and
also round curves. At all times each wheel must be able to travel in
its own plane in spite of the united action of the other two. To run
straight, the axes of all the wheels must obviously be parallel. To run
round a curve, the axis of each must, if continued, pass through the
center of curvature of the curve. If two wheels have a common axis, the
intersection of the two lines forming the axes can only meet in one
point. To steer such a combination, therefore, the plane of the third
wheel only need be turned. If the axis of no two are common, then the
planes of two of the wheels must be turned in order that the three axes
may meet in a point.

Not only does free rolling depend on the suitable direction of the
planes of the wheels, each wheel must be able to run at a speed
proportional to its distance from the point of intersection of the three
axes, i.e., from the ever-shifting center of curvature.

The most obvious way, then, of contriving a three wheeler is to drive
one wheel, steer with another, and leave the third, which must be
opposite the driver, idle. The next in simplicity is to drive with one