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
[Verse: "And God did so that night: for it was dry upon the fleece
only, and there was dew on all the ground,"--JUDGES VI.]
415. _What benefits result from the radiation of heat, &c.?_
But for the _radiation of heat_, we should be subjected to the most
unequal temperatures. The setting of the sun would be like _the going
out of a mighty fire_. The earth would become _suddenly cold_, and
its inhabitants would have to bury themselves in warm covering, to
wait the return of day. By the _radiation_ of heat, an _equilibrium of
temperature_ is provided for, without which we should require a new
order of existence.
The amount of heat which our earth _receives from the sun_, and
the economy of that heat by the laws of _radiation_, _reflection_,
_absorption_, and _convection_, are exactly proportionate to the
necessities of our planet, and the living things that inhabit
it. It is held by philosophers that any change in the orbit of
our earth, which would either increase or decrease the amount of
heat falling upon it, would, of necessity, be followed by the
_annihilation of all the existing races_. The planets Mercury and
Venus, which are distant respectively 37 millions of miles, and 63
millions of miles, from the great source of solar heat, possess
a temperature which would _melt our solid rocks_; while Uranus
(1,800 millions of miles), and Neptune (whose distance from the
sun has not been determined), must receive so small an amount
of heat, that water, such as ours, would become as solid as the
hardest rock, and our atmosphere would be resolved into a liquid!
Yet, poised in the mysterious balance of opposing forces, our orb
flies unerringly on its course, at the rate of 63,000 miles an
hour; preserving, in its wonderful flight, that precise relation
to the sun, which takes from his life-inspiring rays the exact
degree of heat, which, being shared by every atom of matter, and
every form of organic existence, _is just the amount needed to
constitute the heat-life of the world_!
CHAPTER XX.
416. _What is rain?_
Rain is the _vapour of the clouds_ which, being condensed by a fall of
temperature, forms drops of water that descend to the earth.
It is the _return to the earth_ in the form of _water_, of the moisture
_absorbed by the air_ in the form of _vapour_.
417. _Does rain ever occur without clouds?_
It sometimes, but rarely happens, that a sudden transition from
warmth to cold will _precipitate the moisture of the air_, without the
formation of _visible clouds_.
[Verse: "Canst thou lift up thy voice to the clouds, that abundance
of waters may cover thee?"--JOB XXXVIII.]
418. _Why are drops of rain sometimes large and at other times small?_