his from the professor.

"Indeed? Then how do you account for it, professor, that all attempts
to navigate a balloon have hitherto failed?" asked the colonel.

"Begause, my dear zir, the aeronauts have never yed realised all the
requiremends of zuccess," replied the professor, laying down his
magazine as though quite prepared to go thoroughly into the question.

The colonel accepted the challenge, and, rousing himself from his semi-
recumbent posture, said:

"That is quite possible; but what _are_ the requirements of success?"

The professor knocked the ashes out of his meerschaum, refilled it with
the utmost deliberation, carefully lighted it, gave a few vigorous
puffs, and replied:

"The requiremends of zuccess in balloon navigation are very zimilar to
those which enable a man to draverse the ocean. If a man wants to make
a voyage agross the ocean he embargs in a ship, not on a life-buoy. Now
a balloon is nothing more than a life-buoy; id zusdains a man, but that
is all. Id drifts aboud with the currends of air jusd as a life-buoy
drifts aboud with the currends of ocean, and the only advandage which
the aeronaud has over the man with the life-buoy is thad the former can
ascend or descend in search of a favourable air currend, whereas the
ladder is obliged do dake the ocean currends as they come."

"Very true," remarked the colonel; "and what do you deduce from that,
professor?"

"I deduse from thad thad the man who wands to navigade the air musd do
as his brother the sailor does, he musd have a _ship_."

"Well, is not a balloon a sort of air ship?"

"You may gall it zo iv you like, colonel, I do nod; I call it merely a
buoy," returned the professor. "A _ship_ is a zomething gabable of
_moving_ in the elemend which zustains it; a balloon is ingabable of any
indebendend movement in the air; it drifts aboud at the mercy of every
idle wind that blows. Id is like a ship on a breathless sea; withoud
any means of brobulsion the ship lies motionless, or drifts at the mercy
of the currends. Bud give the ship a means of brobulsion, and
navigation ad once begomes bossible. And zo will it be with balloons."

"Well, that has already been tried," remarked the colonel; "but the
buoyancy of a balloon is too slight to permit of its being fitted with
engines and a boiler."

"My vriendt," said the professor impressively, "whad would you think of
the man who tried to pud the engines and boilers of an Atlantic liner i