storm expands so suddenly in rising, that it actu-
ally kicks against the surface air, and drives it
outwards in the direction where the pressure is
least, that is towards the front of the storm.
' Thunderstorms travel along with the move-
ment of the air near their tops, while the preced-
ing inflow in front occurs as in the figure in the
contrary direction. This has given rise to the
saying that they travel against the wind.
There are at least two kinds of thunderstorms.
One is chiefly confined to the equatorial regions
and the summer in high latitudes, and the other
occurs in connection with cyclones in their south-
They are both due to the convectional ascent
of warm moist air, but in the former case it is
locally manufactured during the daytime. In
the latter, it is often imported from a distance.
In the former storms, the cloud is isolated and
continuous often from 1000 feet up to the cirrus
level at 30,000 feet. When it ceases to ascend
it spreads out in a sheet in all directions, so that
a thunderstorm cloud of this kind often pre-
sents in the distance the appearance of a huge
The cyclonic thunderstorms are not so de-
pendent on local sun heat, and frequently occur
at night, and in the winter season in Scotland,
Norway and Iceland. In this case the cooling of
the upper air produces the same effect as the
heating of the lower.
Like the tornadoes they travel mostly east-
wards, and their occurrence generally betokens
WHIRLWINDS, ETC., OF THE ATMOSPHERE. 159
the existence of a cyclone centre to the N. W. in
Europe, and to the S. W. in Australasia.
As long ago as 1752, Franklin proved by his
memorable kite experiment at Philadelphia, the
identity of lightning with electricity artificially
produced on the earth. There is, however, still
very little known as to the exact cause of the
accumulation of electrical potential which finds
vent in the lightning discharge.
The air is ordinarily found to be charged with
a certain amount of positive electricity, while the
earth is usually negative. The concentration ob-
served in thunderstorms, is believed to be due
to the increase in electrical quantity, and rapid
increase in electric potential (or power of do-
ing work) caused by the masses of damp air
which rise up, form towering cumulus clouds,
and discharge their vapour in drops, by conden-
As the tiny droplets of vapour in the cloud
unite to form single large water drops, the elec-
trical charges which always exist to some degree
on their surfaces, become added together. Not
so the surfaces; since the surface of a single
globe is always smaller than that of two globes
which unite together to form it. Consequently,
as more and more droplets unite together, the
electricity has less room over which to spread
itself. It consequently increases in thickness, or
in electrical language, density. It takes 300
trillions of droplets to form a single rain drop,
and it thereupon results that the surface of the
rain drop is one 8-millionth of the area made up
of all the surfaces of its component droplets.
Therefore the density of electricity on the re-
sulting raindrop is 8 million times increased and
l6o THE STORY OF THE EARTH'S ATMOSPHERE.
by a simple electrical law its potential or power
to discharge, is increased 50 billion times.
We can thus understand how it is that so long
as masses of damp air are ascending in sufficient
quantity to cause the great condensation and
rainfall which usually accompanies thunderstorms,
the tremendous discharges of lightning may be
produced and accounted for without recourse to
any special theory of its origin.
Lightning destroys about 250 persons per
annum in America chiefly between April and Sep-
Lightning conductors act by equalising the
flow of electricity between the air and earth and
preventing a disruptive discharge.
They are now generally made of iron and
must always be in contact with damp earth since
they act not by drawing the atmospheric elec-
tricity down, but by allowing the earth electricity
to flow upwards.'
Even in perfectly clear weather there is a con-
stant difference of electrical condition between
the air and earth. In flying kites at Blue Hill
near Boston with steel wire, a conductor has to
be attached to the earth, otherwise the observ-
ers even on a cloudless day experience severe
Lightning is of various kinds. Sometimes it
branches out in all directions from cloud to cloud
and is too far above the earth to strike through
the intervening space. This frequently happens
in the tropics where the author has often wit-
nessed a beautiful electrical storm right over-
head, the thunder of which was inaudible. At
other times, especially in cyclonic thunderstorms,
it occurs in lower clouds and strikes down to
WHIRLWINDS, ETC., OF THE ATMOSPHERE. 161
earth in what is termed forked lightning accom-
panied by loud thunder. Thunder is produced
by the rapid heating and expansion of air by the
discharge passing through it.
The noise is occasioned precisely in the same
way as the sudden generation and expansion of
gas which ensues upon the ignition of gunpowder
in a confined space such as a gun.
The destruction of a tree or house is occa-
sioned in like manner by the expansion of air or
material which is unable to conduct the dis-
charge. Upon a human being the effect is partly
caused by heat and partly by shock to the nerv-
A peculiar form of lightning is occasionally
witnessed in which it descends from the clouds in
a globular form.
These isolated globes of electricity play pecul-
iar pranks, meandering slowly along in the most
wayward and capricious manner, and apparently
doing little damage until they burst. They are
believed to be somewhat of the nature of Leyden
jars in which a layer of air takes the place of the
St. Elmo's fire is an appearance sometimes
seen on the masts of ships in stormy weather.
Each mast head is surrounded by a faint lumi-
nous ball of electric light. It is really a brush
discharge which takes place between the top of
the mast and the highly charged atmosphere over-
The most violent storms of lightning and
thunder in the world are probably to be found in
the north westers of Bengal where the lightning
is continuous for more than an hour at a time.
This is due to the enormous condensation caused
162 THE STORY OF THE EARTH'S ATMOSPHERE.
by the upward convection of the very damp air
of that region. The most awe-inspiring electri-
cal manifestations, however, frequently occur
when a thunderstorm occurs in a region like Col-
orado where the air is usually dry. The author
once experienced a storm at the Colorado Springs
railway station in which every time a flash of
lightning appeared, a miniature flash and loud re-
port were simultaneously observed in the tele-
graph office. The wire of'the conductor outside
was fused, and upon one of the party venturing
out with an umbrella up he returned declaring it
was raining lead.
At the summit of Pike's Peak, 14,000 feet high
in the same district, the observers in the now dis-
continued observatory used occasionally to expe-
rience most disagreeable shocks even in the sim-
ple act of shutting the door, while after walking
across the room they could light the gas with
their fingers. In Canada, in winter when the air
is very dry and frosty, the same phenomena are
It was formerly supposed that thunder and
hail were unknown in the Arctic regions, but Mr.
Harries of the Meteorological Office has recently
shewn that they both occur right up to Spitz-
bergen and are fairly frequent in the Barents
Sea. It seems possible that the warm ocean cur-
rents bring enough warmth and moisture to these
cold regions to cause the vertical instability of
the atmosphere which originates them.
The peculiar arched appearance of the clouds
in norwesters, pamperos, and the arched squalls
of tropical seas and higher latitudes is simply an
effect of perspective caused by a long roll of cloud
advancing athwart the spectator.
SUSPENSION AND FLIGHT IN ATMOSPHERE. 163
SUSPENSION AND FLIGHT IN THE ATMOSPHERE.
THE conquest of the earth by man may be
looked upon as tolerably complete. The con-
quest of the air has so far eluded all his efforts.
Only for short periods and with great trouble and
risk has he been able to mount into the air by the
aid of balloons.
The balloon itself, old though it may appear
to most of us, dates back only 100 years.
Lichtenberg of Gottingen, in 1781, was among
the first to experiment, and made a small balloon
of goat-skin, which ascended in the air when filled
with hydrogen. Thomas Cavallo, an Italian ref-
ugee, about the same time began by blowing soap
bubbles filled with hydrogen, and watching them
mount as the school-boy does to-day. Before he
got much further, a step in advance was made in
France by two brothers, Montgolfier, who curi-
ously enough started by trying to make a cloud
of steam ascend in a silk bag. On lighting a fire
to increase the "cloud " they accidentally struck
on the " hot-air balloon," which has rendered their
The first human being to actually ascend in a
balloon was Pilatre de Rozier on Nov. 21, 1783 ;
but in this case ordinary coal gas was employed,
and has ever since been generally adopted.
Soon after this, in 1785, Blanchard safely
crossed the English channel in a balloon, and
thenceforward ballooning came into fashion,
though at first it was frequently attended with
mishaps and loss of life. The parachute, which
1 64 THE STORY OF THE EARTH'S ATMOSPHERE.
is now so familiar to the world through the re-
cent beautiful descents effected by Baldwin, was
first employed by Garnerin on Oct. 21, 1797. He
then descended safely from a balloon, but experi-
enced violent oscillations. These are now obvi-
ated by means of a central aperture through
which the imprisoned air flows quietly upwards.
The history of the balloon ascents of Lunardi,
Tissandier, Fonvielle, Gay Lussac, Green, Nadar,
Glaisher, and Coxwell is that of continual im-
provement, success, and safety. Their voyages,
particularly those of the two last, have added
considerably to our knowledge of the conditions
of the upper air. Within quite recent years great
strides have been made in the construction of
balloons, chiefly in relation to their use in opera-
tions of war, by the English military balloon
department at Chatham.
The material employed is oxgut, which is ca-
pable of holding pure hydrogen without leakage.
Since pure hydrogen is nearly 2- times as light as
coal gas, balloons filled with it have greater buoy-
ancy and are better fitted to withstand the de-
pressing influence of the wind when captive. A
balloon of this material, which contains 10,000
cubic feet of gas, weighs only 170 Ibs. The top
valve is made of aluminium, and a telephone con-
ductor is arranged for communication between
the occupant of the car and those below. Men
can readily be seen at a distance of two miles
from the car, and general military reconnaissance,
including photography can be conducted with
By the aid of balloons man has certainly suc-
ceeded in attaining suspension in mid air. They
have not, however, aided him in travelling through
bUSPENSION AND FLIGHT IN ATMOSPHERE. 165
the air towards some definite point. If he com-
mits himself to them he must needs go nolens
volens whither the wind may carry him. Far from
having conquered the air as he has conquered the
earth and the sea, he has hardly more power to
guide himself in a balloon than a piece of straw
hurled along by a whirlwind.
Some few years back Messrs. Krebs and Re-
nard in France were supposed to have solved the
problem of the dirigible balloon by means of a
cigar-shaped balloon and a motor which drove a
rotary fan screw at one end ; but though in calm
weather progress at some few miles an hour was
obtained, it was found to be useless against the
wind which ordinarily prevails at any consider-
able height above the earth's surface.
The late Prof. Helmholtz dealt a death-blow
to the practical realisation of the dirigible bal-
loon by shewing on theoretical principles that a
balloon could not be driven against the air at a
rate of more than twenty miles an hour without
destroying its framework. To accomplish aerial
locomotion therefore, we must look elsewhere.
From the earliest times the flight of birds has
attracted the admiration and envy of mankind.
The ancient legend of Icarus who made a pair
of wings and singed them off by flying too near
to the radiant Phoebus, was evidently based on
the desire man has always shewn, to be able to fly
like a bird.
As long ago as 1470, that "preternatural gen-
ius," Leonardo da Vinci, in the intervals of paint-
ing the holy family, etc., amused himself by plan-
ning amongst other things flying machines. More-
over, he appears from his remarks, even then, to
have realised that the main difficulty to be met
1 66 THE STORY OF THE EARTH'S ATMOSPHERE.
with apart from elevating and motive power, was
the question of balance.
The recent accident by which that enthusiastic
soarer Herr Lilienthal of Steglitz lost his life, oc-
curred through his inability to accommodate his
balance to a sudden gust of wind.
The early history of the attempts of man to
fly is not calculated to inspire the human race
with a belief in its intuitive sagacity. For the
most part it is a history of miserable failures and
fatuous inability to realise the feebleness of hu-
man muscular power. The first serious attempt
to grapple scientifically with the problem was
inaugurated by Wenham in 1866 in a paper be-
fore the Aeronautical Society, in which the prin-
ciple of suspension by soaring as well as flapping
was alluded to.
Since that time great progress has been made
in the development of what are termed flying
machines by Prof. Langley of Pittsburgh, Hiram
Maxim of England, Octave Chanute of Chicago,
and Hargrave of Sydney.
In these machines no attempt is made to imi-
tate the flapping by which birds mount into the
air, but only of those principles by which many
of them are enabled to soar or sail with out-
stretched wings when sufficient speed has been
Although it is a fairly safe rule to follow
Nature, exact imitation is by no means in every
case necessary or advisable. Thus, just as in
travel on the earth's surface, it has been found
more convenient to employ the wheel than rap-
idly moving artificial legs, so in the atmosphere,
it is better from an aerial engineering point of
view to analyse the compound movement of a
SUSPENSION AND FLIGHT IN ATMOSPHERE. 167
bird's wing into the two distinct elements, sup-
port and forward propulsion, and deal with them
quite separately. In the case of the bird, the
wing thrusts backwards, and also acts as an in-
clined plane, which, when it is forced horizontally
through the air, converts the pressure into sup-
port. In the artificial flying machine, the back
thrust is given by the fan screw or aerial wheel
at the rear of the plane, and the plane itself re-
mains fixed at a certain angle.
The principle of the inclined plane is strictly
analogous to that by which a kite is suspended
when moored in a breeze. When the breeze fails,
the boy converts his kite into a flying machine
by running with it, and restoring support by the
relative breeze thus created. If we cut the
string of the kite and supply it with a motor and
propelling fan, it will fly itself without the boy's
aid, and become a veritable free flying machine.
The kite, therefore, is the basis of the flying ma-
chine. A flying machine is a self-propelled kite.
There are two actions of the wind on a kite or
inclined plane. Partly it tends to make it drift to
leeward, and partly to lift it upward. Certain
birds, such as the Kestrel hawk, shewn in fig.
(38), the eagle, vulture, and albatross, (especially
the two latter), possess the power of obviating
the tendency to drift, and of keeping themselves
poised, or of sailing for long periods without
flapping by the action of the wind on their wing
planes. The precise way in which this is accom-
plished is not yet fully determined. Maxim
regards it as effected by an intuitive utilisation
on the part of the birds of local upward cur-
rents which exist naturally, or else artificially up
1 68 THE STORY OF THE EARTH'S ATMOSPHERE.
The albatross of the southern seas which the
author has frequently watched for hours and
days together, undoubtedly makes use of the
wind blowing up a wave to restore its lift, after
it has descended nearly to the surface of the
Prof. Langley, on the other hand, attributes
the suspension in both hovering and sailing, more
FIG. 38. Kestrel hawk hovering.
generally to a like intuitive adjustment on the
part of the bird to certain rapid changes which
are found to occur in the speed of the wind.
When a strong gust comes, he slides down a little
to meet it, and overcoming the back drift en-
tirely by his forward momentum, is able to utilise
it simply for lifting him vertically to the same
height he was at before. When the lull occurs,
by lying flatter, he is able in this way to derive a
larger proportion of lift from the lighter wind,
SUSPENSION AND FLIGHT IN ATMOSPHERE. 169
and therefore maintains nearly the same eleva-
tion, and so on.
In the circular sailing so commonly seen when
vultures sight a piece of carrion, the inclination
of the wing planes is similarly increased on the
windward half and decreased on the leeward half
of the circle.
The soaring and sailing of birds is only pos-
sible while the air is in motion. Directly there is
a calm, even the Albatross is obliged to flap.
It is therefore only when a wind is blowing,
that soaring can be exactly imitated by an intel-
ligently controlled flying-machine. In any other
case an artificial wind must be created by means
of the rotating fan-screw in order to ensure sup-
port, and the plane must be kept constantly in-
It will be long before man will be able to gain
such a sense of flight as to be able to dispense
with the motor of his flying machine and sail like
the albatross without any apparent wing motion,
but such a sense will doubtless gradually be de-
veloped as soon as he is fairly launched into the
air, on what is termed the motor aeroplane, and
future generations will witness the ascent of man.
The present position of human flight stands
thus. Mr. Maxim has built a large machine on
the aeroplane principle, which on being propelled
forward, has lifted itself and several people a few
feet from the ground.
Professor Langley has made a small model
machine actuated by a petroleum motor which
has flown for a considerable distance while the
motive power held out.
Mr. Hargrave of Sydney is making a machine
but no actual flight has yet been announced.
170 THE STORY OF THE EARTH'S ATMOSPHERE.
The basis of this machine is the so-called cel-
lular or double plane kite of which Mr. Hargrave
is the inventor, and which has recently been
shown to be the most efficient and stable kite yet
Though a slavish imitation of bird architec-
ture has never found favour with flying machin-
ists, a study of birds, especially the large soaring
and sailing birds, shows, what the Duke of Argyll
in his " Reign of Law " has so lucidly demonstrated,
that birds fly " not because they are lighter, but
because they are immensely heavier than the air.
If they were lighter than the air they might float,
but they could not fly. This is the difference be-
tween a bird and a balloon."
Any machine to travel through the air can
only do so in consequence of its superior momen-
tum. Consequently a flying machine must be
heavy in proportion to the resistance it offers to
Another important point is deduced from the
circumstance that a bird's wing presents a great
length (from tip to tip) and narrow width to the
For example, the wings of that king of flight
the Albatross (Dwnudea exulans) measure 15 feet
from tip to tip and only 8 inches across.
There is a reason for this. When a plane sur-
face is forced through the air, the upward pres-
sure of the air is mostly concentrated near its
front edge. If the surface extended far back
from the edge, its weight would act at some dis-
tance from the front edge. Consequently the
unbalanced pressure of the air would tend to
turn the plane over backwards. If, however, its
width were small, the weight would act so close
SUSPENSION AND FLIGHT IN ATMOSPHERE. 171
to where the resistance acts in the opposite direc-
tion that the forces would neutralise each other
and stability ensue.
Mr. Hargrave has adopted this principle in his
cellular or box kite in fig. (39), whose construe-
tion is sufficiently obvious from the figure to ren-
der detailed description unnecessary.
The dimensions in the figure are in inches.
The length of each cell (from right to left in fig-
ure) is 30 inches, and the width and height and
opening between are about n inches; but these
dimensions may vary, so long as the two cells to-
gether form a nearly square area. An important
feature of this peculiar tailless kite consists of the
172 THE STORY OF THE EARTH'S ATMOSPHERE.
covered-in sides. These ensure stability even bet-
ter than two planes, bent upwards in V shape,
such as the wings of the kestrel when hovering,
and they prevent the kite from upsetting, very
much as the sides of a ship give it stability.
Mr. Maxim once showed the advantage of such
side planes by a simple experiment, in which a
piece of paper, when held horizontally and let
fall to the floor, is seen to execute a series of zig-
zags in the air, frequently ending in its complete
overthrow; whereas, when the same piece of
paper is folded up round the edges like a boat, it
sails to the floor quite evenly, and in a straight
line. The flying machine of the future seems des-
tined to be built somewhat after this pattern.
The prime problem is to launch a stable aero-
plane into the air, -provided with an engine and
screwfan powerful enough to drive it forward at
the velocity required. Mr. Maxim places his
planes at a slope of i in 13, and his practical ex-
periments have shown that the support gained by
the pressure of the air on such planes is more
than twenty times, and the motive power of the
fans'crew thirteen times what had formerly been
supposed. The engine which drives the fan is a
very light one, actuated by petroleum. Hargrave
estimates the entire weight of an engine to gen-
erate 3^ horse power at 30 Ibs. It is placed in
the hollow between the two cells in fig. (3g).
Prof. Langley's recent experiment with his
model over the Potomac showed that the elevat-
ing power derived from such an engine is suffi-
cient. The main difficulty will be to ensure sta-
bility under all conditions, and to accommodate
the apparatus to the varying currents, by the aid
of movable front and side wings. To essay a
SUSPENSION AND FLIGHT IN ATMOSPHERE. 173
journey except in a dead calm, without consider-
able practice, would at first probably end in mis-
haps. An era of preliminary misadventure, in
fact, appears to be almost a necessary corollary
to the establishment of every new form of loco-
motion. That success, however, will eventually
be achieved is now the firm belief of all those who
have studied the question.
The development of the flying machine will
also be much assisted by improvements in the
kite. The most efficient kite will be the most
suitable aeroplane basis for the flying machine.
The kite was first invented by the Chinese gen-
eral, Han Sin, in 206 B. c., for use in war, and was
frequently employed after that date in China, by
the inhabitants of a besieged town, to communi-
cate with the outside world. After this kites ap-
pear to have degenerated into mere toys.
At the middle of the present century, how-
ever, Pocock of Bristol employed them to draw
carriages, and is said to have travelled from Bris-
tol to London in a carriage drawn by kites.
They were also occasionally employed to elevate
thermometers to measure the temperature of the
upper air, by Admiral Back on the Terror, and
Mr. Birt at Kew in 1847.
These observations had been quite forgotten
when the author first suggested the employment
of kites for systematic observations in 1883. It
has since been discovered that Dr. Wilson of