"To begin with," explained his companion, "I have to accomplish the
most astonishing feats in the manner of speed. Literally I have to
travel so fast that I am in two places at once. You will the better
believe me when I tell you who I am,--Jack Frost, at your service, sir.
Now, by what means do you think I manage it ?"

"I 'm sure I don't know. I should like immensely to find out," Lionel
returned.

"How do you get to places yourself?" inquired Jack Frost. "Do you
always run?"

"Oh, no, indeed. I almost always ride on my bicycle. Then I can _go_
like anything, 'specially down _coasts_. Upgrades are kind of hard
sometimes, but not so very. Oh, I can go quick enough when I have my
bicycle."

"Now then," broke in Jack Frost, "you use a bicycle,--that is, a
machine having two wheels. Now _I_ use a something having but one
wheel; consequently it goes twice as fast,--oh! much more than twice as
fast."

"One wheel?" repeated Lionel, thoughtfully; "seems to me I never
heard of that kind of an one."

"Suppose you guess," proposed Jack Frost. "I 'll put it in the form of
a conundrum: If a thing having two wheels is called a _bi_cycle, what
would a thing having but one be called?"