country. At home, one of our most popular
lions is the whispering-gallery of St. Paul's
Cathedral. At Carisbrook Castle, in the Isle
of Wight, is a well two hundred and ten feet
deep, and twelve wide. The interior is lined
by smooth masonry. When a pin is dropped
into the well, it is distinctly heard to strike the
water. Moreover, shouting or coughing into this
well produces a resonant ring of some duration.

Amongst the things not generally known,
Dr. Tyndall informs us that sound still further
resembles light, in being susceptible of refraction.
The refraction of a luminous beam by a
lens is a consequence of the retardation suffered
by the light in passing through the glass.
Sound may be similarly refracted by causing it
to pass through a lens which retards its motion.
Such a lens is formed when we fill a thin
balloon with some gas heavier than air. As an
example, the professor takes a collodion balloon
filled with carbonic acid gas, the envelope being
so thin as to yield readily to the pulses which
strike agninst it, transmitting them to the gas
inside. He then hangs up his watch, close to
the lens; and then, at a distance of four or five
feet on the other side of the lens, he listens,
assisting his ear with a glass funnel, which acts
as an ear-trumpet. By moving his head about
he soon discovers a position in which the ticking
of the watch is particularly loud. This, in
fact, is the focus of the lens. If he moves his
ear away from this focus, the intensity of the
sound decreases. If, when his ear is at the
focus, the balloon be removed, the ticks are
enfeebled; on replacing the balloon, their force
is restored. The lens enables him to hear the
ticks distinctly when they are perfectly
inaudible to the unaided ear. The sound-lens
magnifies small sounds, as the glass lens
magnifies minute objects. Thin india-rubber balloons
form excellent sound-lenses.

The moderate speed of sound in air is the
cause of a number of curious facts which
ignorant people might take for contradictions. For
instance, if a row of soldiers form a circle and
discharge their pieces all at the same time, the
sound will be heard as a single discharge by a
person occupying the centre of the circle. But
if the men form a straight row, and if the
observer stand at one end of the row, the
simultaneous discharge of the men's pieces will be
prolonged to a kind of roar. A company of
soldiers marching to music along a road, cannot
march in time together; for the notes do not reach
those in front and those behind simultaneously.

The velocity of sound in water is more than
four times its velocity in air. The velocity of
sound in iron is seventeen times its velocity in
air. The difference of velocity in iron and in
air may be illustrated by the following instructive
experiment: Choose one of the longest
horizontal bars employed for fencing in Hyde
Park, and let an assistant strike the bar at one
end, while the ear of the observer is held close
to the bar at a considerable distance. Two
sounds will reach the ear in succession; the
first being transmitted through the iron, and
the second through the air. This effect was
observed by M. Biot, in his experiments on the
iron water-pipes of Paris.

Dr. Tyndall's book on Sound contains eight
lectures, all full of novel and instructive matter,
to which the student is progressively initiated.
Even by persons of considerable acquirements
this volume cannot be swallowed as a literary
syllabub. But by devoting two days to the
perusal of each lecture, and twelve more days
to their re-perusal and to getting them up, what
an advance in knowledge is made in a month,
and what a sfock of information is laid in for
the rest of one's life! It is impossible here to
give more than a hint of the things not merely
told, but clearly proved; of sound made
visible; of velocities of sound and sound-waves
measured so simply as to make you wonder you
did not think of it yourself; of harmonics and
their cause demonstrated to the eye, and their
formation rendered as plain to the sight as
their tone is easily recognised by the ear; of
reed-pipes, the organ of voice, and vowel
sounds. In Dr. Tyndall's hands everything is
vocal. Flames sing; burning gas distinguishes
harmony from dissonance; water-jets are
sensible of musical sounds; and, in point of
delicacy, a liquid vein may compete with the ear.

MAJOR MILLIGAN'S MISTAKE

"MISTAKE! my dear sir," said the major,
"faith! it's no mistake at all, at all. No, no,
divil a bit of mistake in it; but I'll jist go and
settle it for you. Wait here a bit till I come
back."

"But, major," I exclaimed, trying to detain
him, "you must tell me what course vou mean
to take."

He put aside my hand, and was gone in a
moment, in spite of my attempts to stop him.

"Confound it!" I muttered; "am I never
to get this affair explained? Here this
Spaniard comes mixing up French and
Spanish in such a way that I can't understand
what he means, except that it is pistols and
coffee for two; and when I tell the major that
I have got into a quarrel, without knowing how,
and that I think there's some mistake, he won't
listen to a word I have to say, but goes off to
settle it without knowing what it is. Well, I
suppose I must wait here till he returns, or I
get a message from the Spaniard."

With these words half aloud to myself, I
turned to the window of the refreshment room,
into which I had lounged from my place in the
theatre. It was full moon, and everything in
the streets of Caracas was as visible as at noon-
day. I gazed for a long time, and was
beginning to think of going away, when I saw a
company of soldiers turn the corner of the street,
and advance to the entrance of the theatre.

"Rather an unusual number of men for
relieving a sentry," said I to myself; "what can
they want?"

The soldiers ascended the steps and halted in