et, whilst we had it against us acting as a deafener."

"Is there any other influence that affects sound besides the wind?"

"Yes, I have already mentioned that temperature has something to do
with it. Sound varies in intensity according to the state of the
atmosphere. If, for example, we ring a small bell in a closed vessel
filled with air, it has been observed that, as the air is withdrawn by
the pump, the sound gradually grows less and less distinct."

"And if a vacuum be formed?"

"Then the sound is totally extinguished."

"So, then," objected Willis, "if two persons were to talk in what you
call a vacuum, they would not hear each other?"

"Two persons could not talk in a vacuum," replied Ernest.

"Why not?"

"Because they would die as soon as they opened their mouths."

"Ah, that alters the case."

"If, on the contrary, a quantity of air or gas were compressed into a
space beyond what it habitually held, then the sound," continued
Ernest, "would be more intense than if the air were free."

"In that case a whisper would be equal to a howl!"

"You think I am joking, Willis; but on the tops of high mountains,
such as the Himalaya and Mont Blanc, where the air is much rarified,
voices are not heard at the distance of two paces."

"Awkward for deaf people!"

"Whilst, on the icy plains of the frozen regions, where the air is
condensed by the severe cold, a conversation, held in the ordinary
tone, may be easily carried on at the distance of half a league."

"Awkward for secrets!"

"And how does sound operate with regard to solid bodies?" inquired
Jack.

"According to the degree of elasticity possessed by their veins or
fibres."

"Explain yourself."

"That is, solid bodies, whose structure is such that the vibration
communicated to some of their atoms circulates through the mass, are
susceptible of conveying sound."

"Give us an instance."

"Apply your ear to one end of a long beam, and you will hear
distinctly the stroke of a pin's head on the other; whilst the same
stroke will scarcely be heard through the breadth of the wood."

"So that, in the first case, the sound runs along the longitudinal
fibres where the contiguity of parts is closer, than when the body is
taken transversely?"

"Just so."

"And across water?"

"It is heard, but more feebly."

For some time Fritz had been closely observing with the telescope a
particular part of the horizon, when all at once he cried, "This time