The objects which come every day before our eyes, the offices which
involuntarily and almost unconsciously we at each moment must perform in
order that we may live, are precisely the subjects concerning which the
mass of mankind are least curious, and of the true nature and utility of
which they are the most completely ignorant. It is thus with the air we
breathe. There is no person but is aware of the necessity of breathing,
and of the motion of the air caused by winds; but how few have asked
themselves, What is air? How much is there of it? Could the same air be
always used for breathing? How do fishes manage living in water in place
of air? Yet the information thus obtainable might be the means of saving
the lives of hundreds, as certainly the ignorance on these points has
been the source of death, by painful and lingering torture, in many
cases. We purpose, therefore, now to give some information about air, to
show the importance of it to mankind, and to indicate how much we owe to
the Omniscient Providence that has given to air the properties that we
find it to possess.
Although "trifles light as air" has become a proverb, yet air is
positively heavy. A hogshead of air weighs about ten ounces; this is
heavier than the gas which is burned in the streets and shops, of which a
hogshead would weigh only seven ounces; and very much heavier than
hydrogen gas, with which balloons were formerly filled, a hogshead of
hydrogen gas weighing only two-thirds of an ounce. A balloon filled with
hydrogen, or even with coal gas, rises into the air, as oil or a cork
rises up through water. The air being thus heavy, presses upon the earth;
and by measuring the degree of pressure we can tell how much air there
is. This is done by an instrument termed a barometer--a glass tube closed
at one end, and which, having been filled with quicksilver, is turned
upside down in a cup containing quicksilver also. The tube being shut at
the top, the air does not press on the quicksilver inside, but presses
upon that in the basin; the quicksilver in the tube, which tends
naturally to fall down into the basin, is thus forced to remain up in the
tube by the pressure of external air; and it rises so high that the
pressure inside, of the quicksilver, and outside, of the air, is equal.
If the pressure of the air diminishes, the quicksilver falls; if the
pressure of the air increases, the quicksilver rises: and as all great
changes of the air are connected with changes of the weather, the
barometer is generally known and consulted as a sort of weather-glass.
Every space of an inch square supports fifteen pounds weight of air; at
the rate of ten ounces to a hogshead, the depth of the air would
therefore be about five miles. But it is much deeper, for air is what is
termed compressible--that is to say, it may by pressure be squeezed into
a smaller bulk; and hence the air next the ground, being compressed by
the portions above it, is much the heaviest portion. At three miles high
a hogshead of air weighs only five ounces, and at eight miles high only
two ounces; hence the limits of the air are much farther removed, and it
is known to extend to at least forty miles.
The office of the air is to support animal life: no animal can live
without air: even fishes require air. The water in which they swim
contains air mixed with it, and this water washing the gills, which are
their lungs, serves to them as the air directly acts on us. If we boil
water until the air is expelled from it, and let it cool in a close
vessel, we may drown a fish by putting it into such water, as easily as a
land animal; it could not breathe. It is thus that in the lakes on the
tops of very high mountains there are no fish. The heights are deserted
by land and by water animals, in consequence of the air being too thin to
support life. The way in which the air acts upon the body is very
interesting. The most abundant element of our food is what the chemists
term carbon, of which, in a gross manner, charcoal may serve as an
example. Now, we eat much more of this than we require for the supply of
our bodies, and it must be got rid of. This is done by its uniting in the
body with a substance termed oxygen, and forming carbonic acid, the sort
of air which boils up in soda water and ginger beer. This dissolves in
the blood, colouring it a deep purple, and escapes from it when by the
action of the heart the black blood is exposed to the action of the air
on the surface of the lungs. Now, the office of the air is to supply this
oxygen which removes the carbon from the blood. But the air is not pure
oxygen. If it were, it would act too violently. An animal which breathes
pure oxygen, becomes flushed, pants violently, and, if not choked, dies
of inflammation of the lungs, produced by the intense action. In the air
we breathe, the oxygen gas is diluted to the proper degree by another
gas, termed nitrogen, which is totally destitute of power; it does of
itself no good and no harm; it is the only substance that could be mixed
in the air we breathe, without interfering in any way. When thus the
blood loses, by exposure to the air in the lungs, its carbonic acid, it
takes oxygen in its place; from dark purple it becomes bright red, and is
then proper to take up a fresh quantity of carbon, and to sustain the
body in health by its removal.
When any thing burns in the air, it is the oxygen which is active. The
nitrogen dilutes here also the oxygen, and keeps its activity down to the
degree most suitable to our wants. If the air were pure oxygen, all our
domestic fires would be violent conflagrations; our iron pokers and
tongs, if heated red hot, would take fire and burn like squibs; no
comfort, no safety for society could exist. But in burning, this oxygen
is destroyed. If a candle be placed lighted under a glass bell, it will,
after a little, go out. The air will become unfit to support combustion.
Here also, as well as in the burning of coals, coke, gas, oil, charcoal,
&c. the oxygen is changed into carbonic acid, and precisely as a fresh
supply of oxygen is necessary for the continuance of life, so is it for
combustion.
The air contains about one part in five of oxygen, and, as has been seen,
this oxygen is liable to continual destruction by the breathing of
animals and the burning of fuel and of lights. An ordinary man spoils in
twenty-four hours 720 cubic feet of air, that is, a mass of air 11 feet 6
inches square and 6 feet thick. The burning of three ounces of charcoal,
or of a mould candle of six to the pound, produces the same effect. It is
not unusual in a factory to burn ten tons of coal a-day, which spoils
3,185,760 cubic feet of air, a mass of a quarter of a mile square and six
feet thick. If we multiply these numbers by the number of inhabitants, of
man and of all other animals upon the earth, and also by the quantity of
fuel burned all over the globe, it will be evident that without some
regulating power superior to all that mere human means could devise, the
air might ultimately become unfit to be the sustenance of living beings,
and all the numerous tribes of animated nature which now adorn its
surface, would be destroyed.
By the all-wise arrangement of Providence, however, the animals, in thus
converting the oxygen of the air into carbonic acid, become the means of
supplying nourishment to another class of beings equally interesting and
numerous. All vegetables breathe; but as animals take in too much carbon
with their solid food, so do plants obtain too little from the substances
that give nourishment to their roots. The animal breathes to give off
carbon, the vegetable breathes to take it up. The two great divisions of
living nature thus act in contrary ways upon the air; the oxygen consumed
by the animal or by combustion, is given out again by the carbon of the
carbonic acid becoming fixed in the plant of which it forms the woody
mass; and thus the composition of the air is kept balanced at its proper
point, and provision for the due nutrition of animals and vegetables is
secured.
The air we breathe serves, however, for other important uses. Without the
air, the fresh breezes which moderate the heats of summer could not
exist, and there would prevail in nature an eternal silence, for it is by
means of air that we not only breathe, but hear. The variety of aspect
given to the sky by the formation and rapid change of clouds, arises from
the mixture of warm and of cold damp air. If there was no air, there
might be dew, but there could never be a cloud.
Without the air we could not have the bright blue sky which gives to our
fine season its greatest charm. The heavens would be a vault of intense
black, in which the sun would appear alone a glaring ball of fire, whose
rays, unmitigated by the air which now absorbs them in their passage
through its mass, would be a continual source of ill. The blue sky, the
bright white clouds, arise from the sun's rays being partly stopped, and
turned from one object to another. The sun's rays really consist of light
of all the colours of the rainbow; of these the red portion is lost in
passing through the air, and the blue remains, giving the colour we
observe. Without the air, a place shaded from the sun would be in
absolute darkness; as it now exists, a quantity of light is scattered
about in every way by the different portions of the air, and thus an
agreeable shade provided in place of the total absence of all light. On
very elevated tops of mountains, where the traveller is placed above the
greater portion of the air, all these effects of its absence which we
have noticed, are found to exist. On the summit of Mont Blanc, a pistol
discharged is scarcely heard, and a companion once out of sight, may be
lost; for neither can he produce any noise by his own exertions, nor
could his voice reach his friends, even if he could speak; the sky is
deep indigo-coloured, or nearly black; and those objects on which the
sun's light does not directly fall, are seen with difficulty.
Such are the uses of the common air we breathe. Such are the benefits we
derive from a blessing, of whose existence when at rest we are almost
unconscious.
ABSENCE OF MIND.--A well-known gentleman of Magdalen College, Cambridge,
had taken his watch from his pocket, to mark the time he intended to boil
an egg for his breakfast, when a friend entering the room, found him
absorbed in some abstruse calculation, with the egg in his hand, upon
which he was intently looking, and the watch supplying its place in the
saucepan of boiling water.
EARLY RISING.--Six or seven hours' sleep is certainly sufficient, and no
one ought to exceed eight. To make sleep refreshing, the following things
are requisite:--To take sufficient exercise in the open air; to avoid
strong tea or coffee; to eat a light supper; and to lie down with a mind
as cheerful and serene as possible. We hardly ever knew an early riser
who did not enjoy a good state of health. It consists with observation,
that all very old men have been early risers. This is the only
circumstance attending longevity, to which we never knew an exception.
Printed and Published every Saturday by GUNN and CAMERON, at the Office
of the General Advertiser, 6 Church Lane, College Green, Dublin.