ker saw that his was one of those minds that grew less calm the
more they were urged, and the excitement of which must be permitted to
wear itself out; he therefore beckoned his sons to leave him to his
own reflections.

The wind still blew a gale, and the pinnace pitched heavily; but the
sun was now beginning to break through the masses of lurid cloud, and
the air was becoming less and less charged with vapor.

"I can descry nothing either," said Becker; "and yet this is the
direction the storm must have driven the sloop."

"The sea is very capricious," suggested Fritz.

"True, but not to the extent of carrying a ship against the wind."

"Unfortunately," said Jack, "it is not on sea as on land, where the
slightest indications of an object lost may lead to its discovery; a
word dropped in the ear of a passer-by might put you on the track, but
here it is no use saying, 'Sir, did you not see the _Nelson_ pass this
way?'"

"Fire a shot," said Ernest; "it may perhaps be heard, now that the air
is less humid."

The two-pounder was ready charged; Fritz struck a light and set fire
to a strip of mimosa bark, with which he touched the piece, and the
report boomed across the waters.

Willis raised his head and listened anxiously, but soon dropped it
again, and resumed his former attitude of hopeless despair.

"It may be," said Ernest, "that the _Nelson_ hears our signal, though
we do not hear hers."

"How can that be?" inquired Jack.

"Why, very easily. Sound increases or diminishes in intensity
according as the wind carries it on or retards it."

"What, then, is sound, that the wind can blow it about, most learned
brother?"

"It is a result of the compression of the air, that from its
elasticity extends and expands, and which causes a sort of trembling
or undulation, similar to that which is observed in water when a stone
is thrown into it."

"And you may add," said Becker, "that bodies striking the air excite
sonorous vibrations in this fluid; thus it rings under the lash that
strikes it with violence, and whistles under the rapid impulsion of a
switch: it likewise becomes sonorous when it strikes itself with force
against any solid body, as the wind when it blows against the cordage
of ships, houses, trees, and generally every object with which it
comes in contact."

"I can understand," replied Jack, "how this sonorous effect is
produced on the particles of air in immediate contact with the object
struck;