Physical Phenomena.
Sound and Light.
Astronomy.
Geology and Paleontology.
Meteorological Phenomena.
Phenomena of Heat.
Magnetism and Electricity.
The Electric Telegraph.
Miscellanea.
Physical Phenomena.
ALL
THE WORLD IN MOTION.Humboldt,
in his
Cosmos,6
gives the following beautiful illustrative proofs of this phenomenon:If,
for a moment, we imagine the acuteness of our senses preternaturally
heightened to the extreme limits of telescopic vision, and bring
together events separated by wide intervals of time, the apparent
repose which reigns in space will suddenly vanish; countless stars
will be seen moving in groups in various directions; nebulæ
wandering, condensing, and dissolving like cosmical clouds; the milky
way breaking up in parts, and its veil rent asunder. In every point
of the celestial vault we shall recognise the dominion of progressive
movement, as on the surface of the earth where vegetation is
constantly putting forth its leaves and buds, and unfolding its
blossoms. The celebrated Spanish botanist, Cavanilles, first
conceived the possibility of “seeing grass grow,” by placing the
horizontal micrometer wire of a telescope, with a high magnifying
power, at one time on the point of a bamboo shoot, and at another on
the rapidly unfolding flowering stem of an American aloe; precisely
as the astronomer places the cross of wires on a culminating star.
Throughout the whole life of physical nature—in the organic as in
the sidereal world—existence, preservation, production, and
development, are alike associated with motion as their essential
condition.THE
AXIS OF ROTATION.It
is remarkable as a mechanical fact, that nothing is so permanent in
nature as the Axis of Rotation of any thing which is rapidly whirled.
We have examples of this in every-day practice. The first is the
motion of
a boy’s hoop.
What keeps the hoop from falling?—It is its rotation, which is one
of the most complicated subjects in mechanics.Another
thing pertinent to this question is,
the motion of a quoit.
Every body who ever threw a quoit knows that to make it preserve its
position as it goes through the air, it is necessary to give it a
whirling motion. It will be seen that while whirling, it preserves
its plane, whatever the position of the plane may be, and however it
may be inclined to the direction in which the quoit travels. Now,
this has greater analogy with the motion of the earth than any thing
else.Another
illustration is
the motion of a spinning top.
The greatest mathematician of the last century, the celebrated Euler,
has written a whole book on the motion of a top, and his Latin
treatise
De motu Turbinis
is one of the most remarkable books on mechanics. The motion of a top
is a matter of the greatest importance; it is applicable to the
elucidation of some of the greatest phenomena of nature. In all these
instances there is this wonderful tendency in rotation to preserve
the axis of rotation unaltered.—Prof.
Airy’s Lect. on Astronomy.THE
EARTH’S ANNUAL MOTION.In
conformity with the Copernican view of our system, we must learn to
look upon the sun as the comparatively motionless centre about which
the earth performs an annual elliptic orbit of the dimensions and
excentricity, and with a velocity, regulated according to a certain
assigned law; the sun occupying one of the foci of the ellipse, and
from that station quietly disseminating on all sides its light and
heat; while the earth travelling round it, and presenting itself
differently to it at different times of the year and day, passes
through the varieties of day and night, summer and winter, which we
enjoy.—Sir
John Herschel’s Outlines of Astronomy.Laplace
has shown that the length of the day has not varied the hundredth
part of a second since the observations of Hipparchus, 2000 years
ago.STABILITY
OF THE OCEAN.In
submitting this question to analysis, Laplace found that the
equilibrium of the ocean is stable if its density is less than the
mean density of the earth,
and that its equilibrium cannot be subverted unless these two
densities are equal, or that of the earth less than that of its
waters. The experiments on the attraction of Schehallien and Mont
Cenis, and those made by Cavendish, Reich, and Baily, with balls of
lead, demonstrate that the mean density of the earth is at least
five
times that of water, and hence the stability of the ocean is placed
beyond a doubt. As the seas, therefore, have at one time covered
continents which are now raised above their level, we must seek for
some other cause of it than any want of stability in the equilibrium
of the ocean. How beautifully does this conclusion illustrate the
language of Scripture, “Hitherto shalt thou come, but no further”!
(Job
xxxviii. 11.)COMPRESSION
OF BODIES.Sir
John Leslie observes, that
air compressed
into the fiftieth part of its volume has its elasticity fifty times
augmented: if it continued to contract at that rate, it would, from
its own incumbent weight, acquire the density of water at the depth
of thirty-four miles. But water itself would have its density doubled
at the depth of ninety-three miles, and would attain the density of
quicksilver at the depth of 362 miles. In descending, therefore,
towards the centre, through nearly 4000 miles, the condensation of
ordinary substances would surpass the utmost powers of conception.
Dr. Young says, that steel would be compressed into one-fourth, and
stone into one-eighth, of its bulk at the earth’s centre.—
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