sly at full speed for
fifty minutes, they became inaudible.

The professor's face, meanwhile, was a picture of ever-growing delight.

"If we can continue to hear the bell for a quarter of an hour I shall be
quite satisfied," he had remarked to Mildmay, as the ship first rose
into the air; "for by that time we shall be quite fifty miles distant
from the beach."

And when the quarter of an hour had elapsed with no perceptible
diminution in the volume of sound, his growing satisfaction had been
faithfully mirrored by the steadily expanding smile upon his expressive
features. Finally, when at length the bells ceased to ring, he
exclaimed--

"Well! who would have believed it? Here have I, a poor silly scientist,
been hoping that my little invention would prove effective for as long a
distance as fifty miles; and behold, at the distance of one hundred and
twenty miles from our friends we have only just lost touch with them.
Let us try back, my friend; turn the ship round, and we will then note
how far we have to run before we can speak clearly to each other."

Mildmay accordingly put the helm hard over, and when the compass showed
that the ship was once more pointing directly toward the spot on the
beach where the remainder of the party had been left, the professor drew
out his watch, and carefully noted the time. Almost immediately the
bells again began to tinkle, at first very faintly and intermittently,
but rapidly increasing in strength as the ship sped back over the ground
that she had traversed a few minutes earlier. By the time that she had
run ten miles on her return journey the bells were again ringing quite
strongly.

"Stop her!" commanded von Schalckenberg. "We are now one hundred and
ten miles from our friends, and I think we ought to be within speaking
distance of them. Let us try."

He touched the red knob of the instrument, and at the same time inserted
the end of the tube in his ear. Almost instantly a faint but quite
distinct shout came to him:

"Hillo, von Schalckenberg, where are you now?" he heard Sir Reginald's
voice inquire.

"We are just one hundred and ten miles distant from you," answered the
professor. "Can you hear me distinctly?"

"Yes, quite distinctly; although your voice does not sound quite so loud
as it did," came the reply. "It sounds as though you were about a
hundred feet away."

"Still, if you can hear me clearly enough to distinguish what I say, it
is good enough.