The reason why : $b a careful collection of many hundreds of reasons for things which, though generally believed, are imperfectly understood. A book of condensed scientific knowledge for the million
John Stuart Mill · en
When grass and corn bend before the wind, and are beaten down by
its force; when the pond forgets its calm, and rises in troubled
waves, casting the flotilla of natural boats that move upon its
surface, in rude disorder upon its windward shore,--the little
storm is but a miniature of those great _hurricanes_ which wrecked
a fleet in the Black Sea, and levelled the encampments of a mighty
army.
When the snow that has gathered upon the house-top, warming
beneath the smiles of the sun, slips from its bed, and drops in
accumulated heaps from the roof,--it is a miniature of those
terrible _avalanches_ which in the Pyrenees bury villages in their
icy pall, and doom man and beast to death.
When the rivulet hurries on its course, and meeting with
obstructions, leaps over them in mimic wrath, overturning some
little raft upon which, perchance, a weary fly has alighted,--it
is a miniature of those _rapids_ on whose banks the hippopotamus
and the alligator yet live; and where, though rarely, man may be
seen directing his raft over the troubled current, amid the rush
of _debris_ from forests unexplored.
And when, in a basin of the rivulet, two opposing currents meet,
and form a little vortex into which insect life and vegetable
fragments coming within the sphere of its influence are drawn,--it
is a miniature of the roaring _whirlpool_, or the wilder
_maelstrom_ of the Norwegian seas.
Nature rehearses all her parts in mild whispers; and for every
picture that she paints, she places a first study upon the canvas.
Man need not go into the heart of her terrors to understand their
laws. Many an unknown Humboldt, sitting by the river's side,
may rejoice in the "aspects of nature," and share the bliss of
knowledge with the great philosopher.
[Verse: "Can any understand the spreadings of the clouds, or the
noise of his tabernacle?"--JOB XXXVI.]
CHAPTER XXXII.
691. _What is a barometer?_
A barometer is an instrument which _indicates the pressure of the
atmosphere_, and which takes its name from two Greek words signifying
_measurer of weight_.
692. _Why does a barometer indicate the pressure of the atmosphere?_
Because it consists of a tube containing _quicksilver_, closed at one
end and open at the other, so that the pressure of the air upon the
open end balances the weight of the column of mercury (quicksilver),
and when the pressure of the air upon the open surface of the mercury
increases or decreases, the mercury _rises or falls_ in response
thereto.
693. _Why is a barometer called also a "weather-glass"?_