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; but how this sound is propagated, I do not see."

"Very likely; but still it travels from particle to particle, in a
circle, at the rate of three hundred and forty yards in a second."

"Three hundred and forty yards in a second!" said Willis, who was
beginning by degrees to recover his self-possession. "Well, that is
what I should call going a-head."

"And by what sort of compasses has this speed been measured, Master
Ernest?"

"The first accurate measurement, Master Jack, was made at Paris in
1738. There are there two tolerably elevated points, namely,
Montmartre and Montlhéry--the distance between these, in a direct
line, is 14,636 _toises_. Cannons were fired during the night, and the
engineers on one of the elevations observed that an interval of
eighty-six seconds and a half elapsed between the flash and the report
of a cannon fired on the other."

"That half-second is very amusing," said Jack laughing; "if there had
been only eighty or eighty-six net, one might still be permitted to
entertain some doubts; but eighty-six and a half admits nothing of the