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
There are many places where remarkable echoes occur. On the
banks of the Rhine, at Lurley, if the weather be favourable, the
report of a rifle, or the sound of a trumpet, will be repeated at
different periods, and with various degrees of strength, from crag
to crag, on opposite sides of the river alternately. A similar
effect is heard in the neighbourhood of some of the Lochs in
Scotland. There is a place at Woodstock, in Gloucestershire, which
is said to echo a sound fifty times. Near Rosneath, a few miles
from Glasgow, there is a spot where, if a person plays a bar of
music upon a bugle, the notes will be repeated by an echo, but a
third lower; after a short pause, another echo is heard, again in
a lower tone; then follows another pause, and a third repetition
follows in a still lower key. The effect is very enchanting. The
whispering galleries of St. Paul's, of the cathedral church of
Gloucester, and of the Observatory of Paris, owe their curious
effects to those laws of the reflection of sound, by which echoes
are produced; but in these cases the effect is assisted by the
elliptical form of the edifice, each person being in the focus of
an ellipse.
CHAPTER XXXV.
748. _What is water?_
Water is a fluid composed of _two_ volumes of _hydrogen_ to _one_
of _oxygen_, or _eight_ parts by weight of _oxygen_ to _one_ of
_hydrogen_. It is nearly colourless and transparent.
749. _Why, if a saucer of water be exposed to the air, will it
gradually disappear?_
Because water is highly expansive, and _rises in thin vapour_, when in
contact with warm and dry air.
[Verse: "Behold there ariseth a little cloud from the sea, of the
bigness of a man's hand. And it came to pass in the meantime, that the
heaven was black with clouds and wind, and there was a great rain."--1
KINGS XVIII.]
750. _Why does steam issue from the spout of a kettle?_
Because the heat of the fire passes into the water, and _drives_ its
atoms apart, making those of them that rise quickly to the surface
_lighter than the air_, upon which they consequently rise.
751. _Why does water become solid when it freezes?_
Because the _latent heat of the water_ passes away from between its
atoms into the air; the atoms, therefore, draw closer together.
752. _Why, if the atoms of water draw closer together when freezing,
does ice expand, and occupy greater space than water?_
Because, _when the atoms of water are congealing_, they do not form a
_compact mass_, but arrange themselves _in groups of crystal points_,
which occupy greater space. Water _contracts_ when freezing until it
sinks to 40 deg., and then it _expands_ as ice is formed.
32 deg. is said to be the _freezing_ point, but it should be
called the _frozen_ point.
753. _Why does water boil?_