Permit me, ladies and gentlemen, to recal to
your memory a few familiar but important scraps
of knowledge, which everybody learns at school,
and portions of which have to be unlearnt afterwards.
What is our day? It might very naturally
have been made the space of time elapsing
between one noon and the noon which precedes
or follows it. We find it more convenient, as
well as more logical, to make it the time between
midnight and midnight. Night, the time for
sleeping, makes a better frontier between one
day and another, than broad daylight, when men
are alert and busy. For instance, the demarcation
between to-day and to-morrow is hardly
recognisable in countries and at seasons when there
is no night—as up at Drontheim with the
midnight sun.

But what make noon and midnight? I need
not inform you that noon and midnight are the
result of two circumstances, namely, of the earth's
shape and of her motion.

First, as to shape: the earth, you are taught,
is an oblate spheroid, that is, a sphere flattened
at the poles, like an orange. It is no such thing,
at least as far as the orange and its flatness are
concerned. To enforce the idea that a very slight
flattening does actually exist, its amount is grossly
exaggerated by the comparison. It is really very
trifling, microscopical.
The earth is a globe, a ball, which is all but a
perfect sphere. The statement of its roundness
is usually supported by a simple test, which
cannot, however, be employed inland. If you stand
on the shore and watch a steamer putting out to
sea, it seems at first to be going up hill, as if it
were climbing the slope of a mountain. Soon, it
is on the edge of the horizon, perched, as it were,
on the top of the hill. Then it goes down the
other side of the hill, its lower part disappearing
little by little, until nothing but the chimney and
its smoke are visible. And then, after a while, it
is gone altogether. The same circumstances
happen, in inverse order, when the steamer comes
into port from the offing. As the very same
appearances occur, at whatever part of the world you
observe vessels at sea, it necessarily follows that
the earth's surface must be circular, and not flat.

But everybody does not dwell on or near the
coast. Millions live and die without ever seeing
the sea, and yet they are equally interested in
the form of their terrestrial tenement. Let them
notice, then, the clouds as they come and go,
especially in a tolerably level country.

We are in the open air, just now, ladies and
gentlemen, and not confined within the four walls
of a lecture-room. We are looking southwards,
and the wind is blowing dead ahead from the
south. And there, on a level with the horizon,
is the top of a great white cumulus cloud. It
rises, and rises, like a ghost coming up from the
stage trap of a theatre. It has already risen to
half its height. It goes on rising. It is all
above the horizon. We now see its base
suspended in the air. It advances towards us. We
are in its shadow. It is now overhead. It sails
on grandly towards the north. Let us turn
round and follow its progress. We are in no
hurry; there is plenty of time.

It goes away from us, sinking down lower the
further it goes. Its base touches our northern
horizon, and our ghostly visitor gradually
descends, disappearing in an erect position, exactly
like our supposed stage phantom. Nothing but
its head is visible now. And now it is gone,
down, down, down. This mode of appearance
and disappearance could only be exhibited by a
cloud floating, at the same elevation, in a spherical
atmosphere enveloping a spherical planet.

The earth, being round, is represented by
means of globes, of various dimensions, each
size professing to furnish us with a diminished
image of our world. But the earth is not
exactly globular; it is flattened at the ends of its
polar diameter. It spins round like a top, or
turns like a joint roasting before the fire; and
the axis on which it spins, the imaginary spit on
which it roasts, is called the polar line, whose
extremities are the north and south poles. Well
on measuring the earth's thickness from one pole
to the other, it is found to be less than if
measured in the direction of the equator. But if we
wanted to represent this flattening of the earth
in a globe thirteen inches in diameter, it would
be imperceptible to the eye and the touch, the
difference between the two thicknesses being
about the thickness of an egg-shell.

On the surface of the earth there are wrinkles
and roughnesses which we call mountains, and
consider immense. They are so, relatively to us;
but to the earth they are as nothing. With all
the pains taken by the manufacturer to render a
thirteen-inch globe perfectly smooth, there will
still remain a few asperities. The biggest of
those asperities, as to height, might be taken to
represent. the elevation of Mont Blanc. How
thin, then, must be our atmosphere, when there
is found to be a difficulty in breathing on such
slightly elevated mountain-tops! Surely we may
call the earth an almost perfect sphere, slightly
varnished over with an atmosphere. Our range
of locomotion is limited to the thickness of the
varnish. In it, we go up in balloons; in it, we
all down precipices and break our necks.
Between the upper and the lower surfaces of this
hallow film, the lightnings dart, the thunders
growl, the rains and hails pelt, and the snows
congeal. Our atmosphere is an enormous
Multum in Parvo.

The earth, which is round, is also in motion.
Fancy a ball from a rifled cannon rushing
onwards, and at the same time spinning on itself;
fancy, while the ball is pursuing its journey, a
multitude of infinitely small creatures to be
produced on its surface, and you have a clear idea of
the earth and its inhabitants. Only, the friction
of the air, through which the cannon-ball
moves, would sadly inconvenience its population;
whereas the earth moves either through empty
space or through an ether which offers no perceptible
resistance.

Another point to be noted as explanatory of
our lengthening day is, that all bodies have