is "" r " last rf'te .
OF THE EARTH'S
DOUGLAS ARCHIBALD, M.A.
FELLOW AND SOMETIME VICE-PRESIDENT
OF THE ROYAL METEOROLOGICAL SOCIETY, LONDON
WITH FORTY-FOUR ILLUSTRATIONS
COPYRIGHT, 1897, 1902,
BY D. APPLETON AND COMPANY.
I HAVE desired in the present little work to
put forward the main features of our knowledge
of the conditions which prevail in our atmosphere
as they are interpreted through the science of to-
day. The Atmosphere, unlike its solid partner,
contains no gold or coal mines with which to
stimulate scientific research. Its study has con-
sequently been somewhat neglected until of late
years, and is even now only just emerging from
the stage of myth and speculation into that of
fact and certainty.
This desirable result has been chiefly attained
by the disuse of vague speculation and the appli-
cation of the known laws of physics.
I have therefore written, not for the minority,
who vaguely wonder at the relation of extraordi-
nary facts and pass on, but for what I believe to
be that much more numerous section who are not
content with a mere collection of facts, but want
to know the reason why.
I have levied largely upon the original works
of the more modern school of meteorologists
which is so ably represented in America, India,
and Germany and am under especial obligations
to those of Prof. Davis of Harvard, Prof. Loomis
6 THE STORY OF THE EARTH'S ATMOSPHERE.
of Yale, Mr. Ferrel of Washington, Prof. Sprung,
and Prof. Waldo.
I have purposely omitted the subject of weather
and descriptions of instruments, and only briefly
touched upon climate, and have rather endeav-
oured to show, especially in the chapter on Flight,
that the Atmosphere possesses growing uses and
interests quite apart from, and in addition to, its
consideration as a vehicle of weather.
I. THE ORIGIN AND HEIGHT OF THE ATMOSPHERE. 9
II. THE NATURE AND COMPOSITION OF THE AT-
III. THE PRESSURE AND WEIGHT OF THE ATMOS-
IV. THE TEMPERATURE OF THE ATMOSPHERE . 31
V. THE GENERAL CIRCULATION OF THE ATMOS-
VI. THE LAWS WHICH RULE THE ATMOSPHERE . 94
VII. THE DEW, FOG, AND CLOUDS OF THE ATMOS-
VIII. THE RAIN, SNOW, AND HAIL OF THE ATMOS-
IX. THE CYCLONES OF THE ATMOSPHERE . . 125
X. THE SOUNDS OF THE ATMOSPHERE . . . 138
XI. THE COLOURS AND OPTICAL PHENOMENA OF
THE ATMOSPHERE . 141
XII. WHIRLWINDS, WATERSPOUTS, TORNADOES, AND
THUNDERSTORMS OF THE ATMOSPHERE . 149
XIII. SUSPENSION AND FLIGHT IN THE ATMOSPHERE 163
XIV. LIFE IN THE ATMOSPHERE 183
LIST OF ILLUSTRATIONS.
Fig. 23 " After the
Fig. i Strato- Cumulus
Fig. 24 Diffusive Limits
of the Component Gases
Fig. 2 Strato-Cumulus
of the Atmosphere
Fig. 25 CirrusCloud (var
Fig. 3 Cirro-Cumulus .
Tracto Cirrus, 1889) .
Fig. 4 ....
Fig. 26 ....
Fig. 5 ....
Fig. 27 ....
Fig. 28 Festooned Cumu-
Fig. 8 Distribution of
Fig. 29 .
ture in Latitude for
Fig. 30 .
Fig. 31 .
January, July, and the
Fig. 32 .
Fig. 33 .
I 3 2
Fig. 9 ....
Fig. 34 .
Fig. 10 ....
Fig. n .
Fig. 36 Tornado Funnel
Fig. 12 .
cioud : .
Fig- 13 .
Fig. 37 Thunderstorm
Fig. 14 .
in Section .
Fig. 15 .
Fig. 38 Kestrel Hawk
Fig. 16 .
Fig. 17 .
Fig. 39 ..-.
Fig. 18 .
Fig. 40 ....
Fig. 19 .
Fig. 41 .
Fig. 20 .
Fig. 42 .
Fig. 21 .
Fig. 22 .
Fig. 43 Yachting in Syd-
THE STORY OF THE EARTH'S
THE ORIGIN AND HEIGHT OF THE ATMOSPHERE,
THE atmosphere of air in which we live and
breathe is really a part of the solid globe on
which we stand.
Until we think of it, we might be inclined to
imagine we were surrounded by mere space, but
when we place our heads under water we find we
can not live more than a few seconds without in-
haling the same air, and we have only to look at
our ships sailing, our windmills rotating, and our
slates blowing off our roofs in a storm, to be cer-
tain that it is just as material as the solid earth
to which it clings.
Its past history, unlike that of its more solid
partner, is not written in the unmistakable lan-
guage of successive rock strata, or fossil remains,
and we can only infer something of its ancient
changes from analogy with what is now occurring
in the sun, and a knowledge of the physical his-
tory of the universe.
If we are to believe the " nebular theory,"
propounded years ago by the great French astron-
omer, La Place, and which, far from being upset,
has rather been confirmed by recent discovery,
10 THE STORY OF THE EARTH'S ATMOSPHERE.
all existing suns and planets have been simply
condensed from clouds or nebulae of matter origi-
nally scattered through space.
By the mutual attraction of their matter
(which force we now term gravitation), these
separate aggregations became highly heated glob-
ular masses, every element of which was at first
in a state of fiery gaseous incandescence. As
they gradually cooled and threw off planetary ex-
crescences, these masses became condensed at first
into liquid spheres or suns, surrounded by atmos-
pheres of the lighter and less condensible gases,
still hot enough to be luminous. Of such a type
is our own sun.
A further stage of cooling took place, par-
ticularly amongst the planetary offspring, during
which the liquid cooled enough on its external
surface to form a thin solid crust, beneath which
it still remained more or less liquid, and above
which enough gases still remained uncondensed
to form a thin atmosphere, through which light
and heat could penetrate, and yet substantial
enough to support animal life. This is the pres-
ent condition of our own planet.
We must not, however, suppose that this state
of things holds on every other planet. The rate
at which such changes progress is different for
The planet Jupiter is still so hot that it is be-
lieved to be partly self-luminous, and its atmos-
phere probably contains clouds and vapours of
substances which on our cooler earth have long
since condensed into liquids or solids. Through
the telescope it is seen to be covered with dense
clouds, and most of its water probably still exists
in the form of vapour (or water gas), and not in
ORIGIN AND HEIGHT OF THE ATMOSPHERE. II
liquid seas as on our own globe. The planet
Mars, on the other hand, has so little water left
in its atmosphere or on its surface that, while
enough remains to supply its polar caps with
snow during the winter, its parched equatorial
deserts are believed by Mr. Lowell, of the Arizona
Observatory, and others who have made it a
FIG. i. Strato-cumulus (low).
special study, to be irrigated thence by the
system of so-called canals which intersect its
Finally, our moon presents a picture of the
condition eventually reached by a small globe
viz., all solid, no liquid, and no gas left. There-
fore, according to our ideas, no life would be
possible on the moon. The liquid, which would
12 THE STORY OF THE EARTH'S ATMOSPHERE.
be chiefly water, has been absorbed into the solid
substance of the moon, while the last relics of
the gaseous atmosphere, which it once must un-
doubtedly have possessed, have been either ab-
sorbed into its mass or else diffused into space
beyond the power of recall by gravitation.
The condition of each globe at present de-
pends chiefly on the rate at which these changes
from all gas, to gas and liquid, and thence to gas,
liquid, and solid, occur /. <?., on their rate of cool-
ing. The larger the globe the longer it takes to
The final condition, however viz., whether a
globe ultimately ceases to possess a liquid or
gaseous covering, and becomes like our moon, or
still retains an atmosphere and oceans like our
earth, depends on the attraction (gravity, as we
term it) by which it holds its gaseous portions to
it. This, again, directly depends on the amount
of -matter it contains, and therefore again upon
its size. Thus, our earth will probably never lose
its atmosphere altogether, though considerable
quantities of the lighter gases, such as hydrogen,
have no doubt already escaped into space.
The fact, therefore, that we possess at the
present time a gaseous atmosphere of exactly
that particular degree of tenuity that suits our
breathing apparatus, remarkable though it may
seem, is a direct consequence of the particular
size of the globe on which we stand.
Back through the corridors of time, before the
earth had sufficiently cooled to acquire a solid
crust, we were a little sun, with an atmosphere of
hot, turbid, metallic vapours which poured down
metallic rain, only to be boiled off again on
approaching the heated surface. After a time,
ORIGIN AND HEIGHT OF THE ATMOSPHERE. 13
however, such metallic rain would cease to rise
again, and remain a part of the solidifying earth,
and by the time that geologic history com-
menced and the surface was cool enough to ad-
mit of animal and vegetable growth, the atmos-
phere must have been practically as clear as it is
In proof of this we find that those remarkable
trilobites or sea-lice of the Silurian period, which
is nearly the oldest of which we have any knowl-
ledge, were endowed with organs of vision, which
shew that as much light penetrated the seas then
as now. The atmosphere, therefore, must have
been equally transparent. Doubtless, more va-
pour and carbonic acid were present. Indeed,
some of the latter has since been locked up in a
solid form in the coal measures and limestone
rocks of subsequent epochs.
Continuing our globe history, there came a
time when the atmosphere, after being heated
mostly from the still warm earth, began to find
its solid partner no longer the warm friend of its
youth, and found itself compelled to depend on
the solar beams, albeit after they had travelled
through ninety-three million miles of space, to
protect it from the terrible cold of space. By
receiving and entrapping such rays, it is even now
enabled to keep some 500 Fahr. warmer than
outside space, while the heat which at present
reaches it from the earth is estimated as being
barely enough to raise it -j-J^ths of a degree in
The atmosphere of our planet, therefore, is
our own individual property, and in no sense
part of a universal atmosphere spread all over
space. In fact, if such a general atmosphere ex-
14 THE STORY OF THE EARTH'S ATMOSPHERE.
isted at all, it has been calculated by Dr. Thiesen
of Berlin that our sun would, by virtue of its
enormous size a million times that of our earth
and gravity, which is twenty-seven times
greater, attach to itself a gaseous covering or
atmosphere, which would be as dense as our own,
far beyond the orbit of Venus. This, however,
is known to be contrary to fact.
FIG. 2. Strato-cumulus (high).
The sun's atmosphere is not more than about
500,000 miles deep, while that of the earth is cer-
tainly not more than 100 miles.
The height of our atmosphere has never been
ORIGIN AND HEIGHT OF THE ATMOSPHERE. 15
measured as we measure distances on the earth's
surface, for the very simple reason that we can
never hope to reach the top. Indeed, we should
find it very difficult to know where the top was,
even if we were able to approach it, since the air
would shade off so gradually into where it sud-
denly changed into the vacuum of space that we
should with difficulty discover the place where
we could say " thus far and no farther."
We can, however, arrive at some knowledge
of the probable height to which the air exists in
such quantity as to possess weight and resistance
by calculation of the rate at which the pressure
of the atmosphere diminishes as we ascend, and
also by observation of the duration of twilight
and the heights at which meteorites (or, as they
are still popularly termed, falling stars) are
Living as we do at the base of our ocean of
air, like the flat-fish live at the bottom of the
ocean of water, we are absurdly ignorant of the
condition of the atmosphere a few miles overhead.
The highest ascent made by man up moun-
tains is believed to be that of Zurbriggen on
Aconcaqua, when he reached about 24,000 feet,
or a little over 4 miles, while the highest in a
balloon was that made by Dr. Berson of Berlin,
who in 1894 ascended to a height of 30,000 feet.
Some years ago, in 1862, Glaisher and Coxwell
made a memorable ascent over Wolverhampton,
when they became unconscious at 29,000 feet,
after which they were supposed to have ascended
for a short time, to nearly 36,000 feet, but in Dr.
Berson's case, by inhaling oxygen he was able to
observe his instruments and carefully note the
conditions around him.
1 6 THE STORY OF THE EARTH'S ATMOSPHERE.
His thermometer went down to 54 degrees
below zero Fahr., while the mercury in his bar-
ometer sank from 30 to 9 inches. Six miles is
probably the limit to which man will ever care to
ascend into the atmosphere, since above this
height he can only survive by the aid of artificial
assistance. For permanent habitation it is found
to be prejudicial to live at greater heights than
15,000 feet, so that it is only within a thin slice
of our atmospheric blanket that human life is
lived. Actually, the marvellous complexity of
human thought and action, and the development
of modern civilisation on this earth, has taken
place, and will probably always remain confined
within the vertical distance of a London shilling
cab fare above the surface.
Apart from direct measurement, the pressure
of the atmosphere gives us some clue to its height
as well as to its weight. From the pressure obser-
vations alone, it ought to disappear somewhere
about 38 miles, since at that height the mercury
column of the barometer, which measures the
weight of air above, would tend to disappear.
Observations of meteorites, however, whose ap-
pearance depends upon their heating to incan-
descence by friction against a resisting medium,
shew that some air exists at 100 miles, though
at such great altitudes it is probably in a con-
dition of extreme rarity. Observations of the
duration of twilight, which is due to reflection
from particles of dust and air, gave about 50
miles as the limit. Practically, therefore, we
may take 50 miles to be about the limit up to
which the atmosphere exists in a coherent form
as we know it near the earth's surface.
NATURE AND COMPOSITION OF ATMOSPHERE. 17
THE NATURE AND COMPOSITION OF THE
To one of those superior beings who, we be-
lieve, inhabit the celestial regions, it must have
been infinitely pathetic to see the poor human mites
on this planet struggling for centuries through
the mist of error and superstition, until they
finally discovered one day the composition of the
atmosphere in which they lived. By the Greeks
FIG. 3. Cirro-cumulus.
the air was considered to be one of the four ele-
ments, and it was not until the middle of the last
century that Priestley discovered that air was a
1 8 THE STORY OF THE EARTH'S ATMOSPHERE.
mixture of oxygen and nitrogen, and that its
neutral character was due to the blending of a
most active element, oxygen, with a most inactive
A slight difference in the proportion of either
element would be fatal to life as we know it.
With more oxygen in the air our lives, short
enough as they are, would be still more brief, and
though we might be more witty and brilliant, we
should live in a state of such mental and physical
intoxication that we should never be able to sit
down quietly to do any solid work. In fact, the
human race would be converted into a number of
thoughtless, reckless, frivolous beings, who would
probably end by destroying each other in a frenzy
of over-excitement. On the other hand, too much
nitrogen would reduce us to such a degree of
dulness and inertia that our supposed national
characteristics would be intensified and we should
become like a row of statues or mummies, with,
out action or passion, lifeless in fact, matter
without motion. The existing proportion there-
fore is decidedly adapted to our present require-
ments. The average proportion in which the two
principal components of the atmosphere are found
to occur is 21 of oxygen to 79 of nitrogen by vol-
ume, and 23 of oxygen to 77 of nitrogen by weight.
The proportion in which the remaining con-
stituents enter is so small that it may be practi-
cally neglected when we consider the physical
properties of the atmosphere, though it cannot
be neglected when we regard its vital and chemi-
cal functions. The other constituents are car-
bonic acid, which occupies i o jnr tns by volume,
traces of ammonia, ozone, and the recently dis-
NATURE AND COMPOSITION OF ATMOSPHERE. 19
Oxygen, which forms one-fifth of the atmos-
phere, represents the active vitalising principle, a
large proportion of which, by its former chemical
union with certain terrestrial elements, such as
silicon and aluminium, has solidified into large
rock masses, by union with hydrogen, has pro-
duced the liquid ocean, and the gaseous vapour
of the atmosphere, and which, by its chemical
union with carbon through the tissues of plants
and animals, develops the energy which is mani-
fested in their life and movements.
Owing to the fact that the density of oxygen
is very nearly the same as that of nitrogen, and
to the constant mixture which takes place, the
proportions in which they are found at high ele-
vations differ but little from those at sea-level.
Thus in a balloon ascent at Kew, the percent-
age of oxygen present at a height of 18,630 feet
was found to be 20.88, while it was 20.92 at the
surface. Here it varies chiefly according to the
lack of ventilation and the number of people who
inhabit confined spaces. In the pit of a theatre
the percentage is 20.7, in a law court 20.6, and in
the gallery of a theatre about 20.5.
So far as its chemical properties are con-
cerned, therefore, the atmosphere at great heights
is just as suitable for man as it is at sea-level.
The only practical drawbacks arise from its
greater rarity and cold, as we ascend from the
surface. / v
The Nitrogen, which forms three fifths of the
atmosphere, represents the inert, negative ele-
ment which, though not actively hostile to life,
by diluting the oxygen, lessens the activity and
rapidity of the energy developed by the latter's
combustion, and thus tends to prolong life, which
20 THE STORY OF THE EARTH'S ATMOSPHERE.
would be used up too rapidly in pure oxygen. It
would not be easy, in fact, to find any other dilu-
ent of oxygen which could take the place of
nitrogen without producing poisonous effects like
those of carbonic acid.
Regarded from a physical point of view, nitro-
gen, being slightly less dense than oxygen in the
proportion of 97 to no, renders the air a better
vehicle for sound, support, and power than it
would be otherwise.
Nitrogen is also absorbed from the atmos-
phere by plants, through the agency of those
marvellous little bacilli parasites, the Nitragin,
which have recently been shewn by Prof. Dobb6
to nourish certain plants by abstracting the nitro-
gen from the air and passing it into the substance
of the plants. Each plant, moreover, appears to
be fed by its own special bacillus, but starved by
that of any other plant.
The carbonic acid only forms a very small
percentage of the air, but nevertheless plays an
important part in the operations of nature.
Animals consume oxygen and exhale carbonic
acid as a product of their respiration. Plants, on
the other hand, under the action of light on their
green cells decompose the carbonic acid, absorb
the carbon, and liberate the oxygen. By these
means the balance between supply and consump-
tion is about maintained.
In former periods of the earth's history the
amount of carbonic acid in the atmosphere was
probably much greater than at present. Espe-
cially during the carboniferous epoch of geology,
when owing to special climatic conditions enor-
mous quantities of trees and ferns grew which
abstracted the carbon from the then existing at-
NATURE AND COMPOSITION OF ATMOSPHERE. 21
mosphere, and by burying it for centuries in the
solid form of coal all over the world materially re-
duced the subsequent proportion of carbonic acid
from what had previously existed. Though .03
per cent., the amount existing at present seems a
small quantity, it is yet as we know, enough to
supply all the vegetable world with its solid
Huxley once calculated the amount of this gas
which is contained in a section of the atmosphere
resting on a square mile to be as much as 13,800
tons, while the amount of solid carbon which could
be extracted from such a quantity of the gas would
be about 3700 tons, enough to supply a small for-
est of trees weighing 7400 tons.
Ozone, of which traces exist in the atmosphere,
is a peculiar form of oxygen, a molecule of which
is composed of two atoms linked together, and a
third which, on the principle of two is company
and three is none, is inclined to walk off whenever
it meets with a suitable companion. Fortunately
for man the tastes of this third atom are distinctly
low, since it has a partiality for sewers and places
where matter is decomposing and which by its
active oxidising power it renders neutral and
harmless. Since towns usually contain more of
such deleterious conditions than the country,
more ozone is found on their windward than on
their leeward sides.
Ozone prevails most in the spring months and
least in the autumn, and while it probably acts
beneficially as a rule, by its active oxidation of
poisonous gases, its excess is associated with the
prevalence of certain forms of catarrhal disease.
Traces of ammonia occur which help to supply
nitrogen to the soil and plants when washed down
22 THE STORY OF THE EARTH'S ATMOSPHERE.
by rain. Every year about 30 Ibs. of ammonia arc
carried down to each acre of ground. The above
constituents are blended together like different
brands' of spirit, but are free to enter into com-
bination with other substances. This freedom of
contract is implied in the term mechanical union,
which is employed to distinguish the mixture of
oxygen and nitrogen forming atmospheric air
from that of the chemical union between oxygen
and hydrogen in the compound water.
The vapour of water which as an invisible gas
is generally more or less associated with dry air
may be looked upon as a separate atmosphere of
gaseous water. The fact, however, that it is im-
possible to distinguish it from dry air by sight or
smell, and that until it condenses out of the latter
as rain or cloud it virtually forms one of its com-
ponents, makes it desirable for us to regard it in
this light, if we are careful to remember that its
quantity (generally about i per cent, by weight)
is ever varying, and that the volume of dry air it
displaces and occupies itself, depends on the tem-
perature as well- as the mass of it present. When
it occurs as an invisible gas it is |ths as dense as
dry air at the same temperature and pressure.
The peculiarity of the position of aqueous vapour
is, that if it existed alone on the earth, there would
be only one temperature at which it would change
from a gas into a liquid, and therefore only one
level at which cloud would form and whence rain
would descend altering with the time of day and
Since, however, it exists in combination with
air, it spreads upwards until it arrives at the par-
ticular temperature at which the air fails to sup-
port it in solution, when a layer of cloud forms
NATURE AND COMPOSITION OF ATMOSPHERE. 23
and perhaps rain falls. After this an interval oc-