<h2><SPAN name="CHAPTER_VIII" id="CHAPTER_VIII">CHAPTER VIII</SPAN><br/> <span class="subhead"><span class="smcap">Ships that Sail the Skies</span></span></h2>
<p class="drop-cap3"><span class="smcap1">Shortly</span> after the Civil War broke out,
Thaddeus S. C. Lowe, an enthusiastic
American aëronaut, conceived the idea of sending
up scout balloons to reconnoiter the position
of the enemy. These balloons were to be
connected by telegraph wires with the ground,
so that they could direct the artillery fire. The
idea was so novel to the military authorities of
that day that it was not received with favor.
Balloons were looked upon as freak inventions,
entirely impracticable for the stern realities
of war; and as for telegraphing from a balloon,
no one had ever done that before.</p>
<div id="ip_148" class="figcenter" style="width: 481px;">
<ANTIMG src="images/i_148.jpg" width-obs="481" height-obs="240" alt="" /><br/>
<div class="captionl">(C) Underwood & Underwood</div>
<div class="caption0">A big German Zeppelin that was forced to come down on French soil</div>
</div>
<p>But this enthusiast was not to be daunted,
and he made a direct appeal to President Lincoln,
offering to prove the practicability of this
means of scouting. So he took his balloon to
Washington and made an ascent from the
grounds of the Smithsonian Institution, while<span class="pagenum"><SPAN name="Page_149" id="Page_149">149</SPAN></span>
the President came out on the lawn south of the
White House to watch the demonstration. In
order to test him, Mr. Lincoln took off his hat,
waved his handkerchief, and made other signals.
Lowe observed each act through his field-glasses
and reported it to the President by telegraph.
Mr. Lincoln was so impressed by the demonstration
that he ordered the army to use the observation
balloon, and so with some reluctance
the gas-bag was introduced into military service,
Professor Lowe being made chief aëronautic
engineer. Under Lowe's direction the observation
balloons played an important part in the
operations of the Union Army.</p>
<div id="ip_149" class="figcenter" style="width: 351px;">
<ANTIMG src="images/i_149.jpg" width-obs="351" height-obs="460" alt="" /><br/>
<div class="captionl">Courtesy of "Scientific American"</div>
<div class="caption0">Observation Car lowered from a Zeppelin sailing
above the clouds</div>
</div>
<p>On one occasion a young German military
attaché begged the privilege of making an ascent
in the balloon. Permission was given and
when the German officer returned to earth he
was wildly enthusiastic in praise of this aërial
observation post. He had had a splendid view
of the enemy and could watch operations
through his field-glasses which were of utmost
importance. Realizing the military value of
the aircraft, he returned to Germany and urged
military authorities to provide themselves with
captive balloons. This young officer was Count<span class="pagenum"><SPAN name="Page_150" id="Page_150">150</SPAN></span>
Ferdinand von Zeppelin, who was destined later
to become the most famous aëronautic authority
in the world and who lived to see Germany
equipped with a fleet of balloons which were
self-propelling and could travel over land and
sea to spread German frightfulness into England.
He also lived to see the virtual failure
of this type of war-machine in the recent great
conflict, and it was possibly because of his deep
disappointment at having his huge expensive
airships bested by cheap little airplanes that
Count von Zeppelin died in March, 1917. However,
he was spared the humiliation of seeing a
fleet of Zeppelins lose their way in a fog and
fall into France, one of them being captured before
it could be destroyed, so that all its secrets
of construction were learned by the French.</p>
<h3>THE WEIGHT OF HYDROGEN</h3>
<p>Before we describe the Zeppelin airships and
the means by which they were eventually overcome,
we must know something about the principles
of balloons. Every one knows that balloons
are kept up in the air by means of a very
light gas, but somehow the general public fails
to understand why the gas should hold it up.<span class="pagenum"><SPAN name="Page_151" id="Page_151">151</SPAN></span>
Some people have a notion that there is something
mysterious about hydrogen gas which
makes it resist the pull of gravity, and that the
more hydrogen you crowd into the balloon the
more weight it will lift. But hydrogen has
weight and feels the pull of gravity just as air
does, or water, or lead. The only reason the
balloon rises is because it weighs less than the
air it displaces. It is hard to think of air
as having weight, but if we weigh air, hydrogen,
coal-gas, or any other gas, in a vacuum, it will
tip the scales just as a solid would. A thousand
cubic feet of air weighs 80 pounds. In other
words, the air in a room ten feet square with a
ceiling ten feet high, weighs just about 80
pounds. The same amount of coal-gas weighed
in a vacuum would register only 40 pounds;
while an equal volume of hydrogen would weigh
only 5½ pounds. But when we speak of volumes
of gas we must remember that gas, unlike
a liquid or a solid, can be compressed or expanded
to almost any dimensions. For instance,
we could easily fill our room with a ton
of air if the walls would stand the pressure; or
we could pump out the air, until there were but
a few ounces of air left. But in one case the<span class="pagenum"><SPAN name="Page_152" id="Page_152">152</SPAN></span>
air would be so highly compressed that it would
exert a pressure of about 375 pounds on every
square inch of the wall of the room, while in
the other case its pressure would be almost infinitesimal.
But 80 pounds of air in a room
of a thousand cubic feet would exert the same
pressure as the atmosphere, or 15 pounds on
every square inch. And when we say that a
thousand cubic feet of hydrogen weighs only a
little over 5 pounds, we are talking about hydrogen
at the same pressure as the atmosphere.</p>
<p>Since the hydrogen is sixteen times lighter
than air, naturally it will float in the air, just as
a piece of wood will float in water because it is
lighter than the same volume of water. If we
surrounded the thousand cubic feet of hydrogen
with a bag so that the gas will not diffuse
into the air and mix with it, we shall have a
balloon which would float in air provided the bag
and the hydrogen it contains do not weigh more
than eighty pounds. As we rise from the surface
of the earth, the air becomes less and less
dense, or, in other words, it becomes lighter,
and the balloon will keep on rising through the
atmosphere until it reaches a point at which its<span class="pagenum"><SPAN name="Page_153" id="Page_153">153</SPAN></span>
weight, gas-bag and all, is exactly the same as
that of an equal volume of air.</p>
<p>But there are many conditions that affect the
height to which the balloon will ascend. The
higher we rise, the colder it is apt to become,
and cold has a tendency to compress the hydrogen,
collapsing the balloon and making it relatively
heavier. When the sun beats upon a balloon,
it heats the hydrogen, expanding it and
making it relatively lighter, and if there is
no room for this expansion to take place in the
bag, the bag will burst. For this reason, a big
safety-valve must be provided and the ordinary
round balloon is open at the bottom so that the
hydrogen can escape when it expands too much
and the balloonist carries ballast in the form of
sand which he can throw over to lighten the
balloon when the gas is contracted by a sudden
draft of cold air.</p>
<p>Although a round balloon carries no engine
and no propeller, it can be guided through the
air to some degree. When an aëronaut wishes
to go in any particular direction, he sends up
his balloon by throwing out ballast or lowers it
by letting out a certain amount of gas, until<span class="pagenum"><SPAN name="Page_154" id="Page_154">154</SPAN></span>
he reaches a level at which he finds a breeze
blowing in the desired direction. Such was
the airship of Civil War times, but for military
purposes it was not advisable to use free
balloons, because of the difficulty of controlling
them. They were too liable to fall into the
hands of the enemy. All that was needed was
a high observation post from which the enemy
could be watched, and from which observations
could be reported by telegraph. The balloon
was not looked upon as a fighting-machine.</p>
<h3>ZEPPELIN'S FAILURES AND SUCCESSES</h3>
<p>But Count Zeppelin was a man of vision. He
dreamed of a real ship of the air—a machine
that would sail wherever the helmsman chose,
regardless of wind and weather. Many years
elapsed before he actually began to work out
his dreams, and then he met with failure after
failure. He believed in big machines and the
loss of one of his airships meant the waste of
a large sum of money, but he persisted, even
though he spent all his fortune, and had to go
heavily in debt. Every one thought him a crank
until he built his third airship and proved its
worth by making a trip of 270 miles. At once<span class="pagenum"><SPAN name="Page_155" id="Page_155">155</SPAN></span>
the German Government was interested and saw
wonderful military possibilities in the new craft.
The Zeppelin was purchased by the government
and money was given the inventor to further his
experiments.</p>
<p>That was not the end of his failures. Before
the war broke out, thirteen Zeppelins had been
destroyed by one accident or another. Evidently
the building of Zeppelin airships was not
a paying undertaking, although they were used
to carry passengers on short aërial voyages.
But the government made up money losses and
Zeppelin went on developing his airships.</p>
<p>Of course, he was not the only one to build
airships, nor even the first to build a dirigible.
The French built some large dirigibles, but
they failed to see any great military advantage
in ships that could sail through the air, particularly
after the airplane was invented, and
so it happened that when the war started the
French were devoting virtually all their energies
to the construction of speedy, powerful
airplanes. As for the British, they did not pay
much attention to airships. The idea that their
isles might be attacked from the sky seemed an
exceedingly remote possibility.</p>
<p><span class="pagenum"><SPAN name="Page_156" id="Page_156">156</SPAN></span></p>
<h3>RIGID, SEMI-RIGID, AND FLEXIBLE BALLOONS</h3>
<p>Count Zeppelin always held that the dirigible
balloons must be rigid, so that they could be
driven through the air readily and would hold
their shape despite variations in the pressure of
the hydrogen. The French, on the other hand,
used a semi-rigid airship; that is, one in which a
flexible balloon is attached to a rigid keel or
body. The British clung to the idea of an entirely
flexible balloon and they suspended their
car from the gas-bag without any rigid framework
to hold the gas-bag in shape. In every
case, the balloons were kept taut or distended
by means of air-bags or ballonets. These air-bags
were placed inside the gas-bags and as the
hydrogen expanded it would force the air out
through valves, but the hydrogen itself would
not escape. When the hydrogen contracted, the
air-bags were pumped full of air so as to maintain
the balloon in its fully distended condition.
Additional supplies of compressed hydrogen
were kept in metal tanks.</p>
<div id="ip_156" class="figcenter" style="width: 352px;">
<ANTIMG src="images/i_156.jpg" width-obs="352" height-obs="227" alt="" /><br/>
<div class="captionl">(C) Underwood & Underwood</div>
<div class="caption0">Giant British Dirigible built along the lines of a Zeppelin</div>
</div>
<div id="ip_156b" class="figcenter" style="width: 349px;">
<ANTIMG src="images/i_156b.jpg" width-obs="349" height-obs="248" alt="" /><br/>
<div class="captionl">(C) Underwood & Underwood</div>
<div class="caption0">One of the engine cars or "power eggs" of a British Dirigible</div>
</div>
<p>In the Zeppelin balloon, however, the gas was
contained in separate bags which were placed in
a framework of aluminum covered over with<span class="pagenum"><SPAN name="Page_157" id="Page_157">157</SPAN></span>
fabric. Count Zeppelin did not believe in placing
all his eggs in one basket. If one of these
balloons burst or was injured in any way, there
was enough buoyancy in the rest of the gas-bags
to hold up the airship. As the Zeppelins were
enormous structures, the framework had to be
made strong and light, and it was built up of a
latticework of aluminum alloy. Aluminum itself
was not strong enough for the purpose, but
a mixture of aluminum and zinc and later another
alloy known as duralumin, consisting of
aluminum with three per cent of copper and
one per cent of nickel, provided a very rigid
framework that was exceedingly light. Duralumin
is four or five times as strong as aluminum
and yet weighs but little more.</p>
<div id="ip_157" class="figcenter" style="width: 476px;">
<ANTIMG src="images/i_157.jpg" width-obs="476" height-obs="352" alt="" /><br/>
<div class="captionl">Photograph by International Film Service</div>
<div class="caption0">Crew of the C-5 (American Coastal Dirigible) starting for Newfoundland
to make a Transatlantic Flight</div>
</div>
<p>The body of the Zeppelin is not a perfect circle
in section, but is made up in the form of a
polygon with sixteen sides, and the largest of the
Zeppelins used during the war contained sixteen
compartments, in each of which was placed a
large hydrogen gas-bag. A super-Zeppelin, as
the latest type is called, was about seventy-five
feet in diameter and seven hundred and sixty
feet long, or almost as long as three New
York street blocks. In its gas-bags it carried<span class="pagenum"><SPAN name="Page_158" id="Page_158">158</SPAN></span>
two million cubic feet of hydrogen and although
the whole machine with its fuel, stores, and passengers
weighed close to fifty tons, it was so
much lighter than the air it displaced that it
had a reserve buoyancy of over ten tons.</p>
<h3>KEEPING ENGINES CLEAR OF THE INFLAMMABLE HYDROGEN</h3>
<p>As hydrogen is a very inflammable gas, it is
extremely dangerous to have an internal-combustion
engine operating very near the gas-bags.
In the super-Zeppelins the engines were
placed in four cars suspended from the balloon.
There was one of these cars forward, and one
at the stern, while near the center were two cars
side by side. In the rear car there were two
engines, either of which could be used to drive
the propeller. By means of large steering rudders
and horizontal rudders, the machine could
be forced to dive or rise or turn in either direction
laterally. The pilot of the Zeppelin had
an elaborate operating-compartment from
which he could control the rudders, and he also
had control of the valves in the ballonets so that
by the touch of a button he could regulate the
pressure of gas in any part of the dirigible.<span class="pagenum"><SPAN name="Page_159" id="Page_159">159</SPAN></span>
There were nineteen men in the crew of the
Zeppelin—two in the operating-compartment,
and two in each of the cars containing engines,
except for the one at the stern in which there
were three men. The other men were placed
in what was known as the "cat walk" or passageway
running inside the framework under
the gas-bags. These men were given various
tasks and were supposed to get as much sleep
as they could, so as to be ready to replace the
other men at need.</p>
<p>The engine cars at each side of the balloon
were known as power eggs because of their general
egg shape. At the center of the Zeppelin
the bombs were stored, and there were electro-magnetic
releasing-devices operated from the
pilot's room by which the pilot could drop the
bombs whenever he chose. The Zeppelin also
carried machine-guns to fight off airplanes.
Gasolene was stored in tanks which were placed
in various parts of the machine, any one of
which could feed one or all of the engines, and
they were so arranged that they could be thrown
overboard when the gasolene was used up, so
as to lighten the load of the Zeppelin. Water
ballast was used instead of sand, and alcohol<span class="pagenum"><SPAN name="Page_160" id="Page_160">160</SPAN></span>
was mixed with the water to keep it from freezing.
The machine which came down in French
territory and was captured before it could be
destroyed by the pilot, found itself unable to
rise because in the intense cold of the upper
air the water ballast had frozen, and it could
not be let out to lighten the load of the Zeppelin.</p>
<div class="center"><div class="container">
<div id="ip_160" class="figleft" style="width: 249px;">
<ANTIMG src="images/i_160.jpg" width-obs="249" height-obs="339" alt="" /><br/>
<div class="captionl">Photograph from Kadel & Herbert</div>
<div class="caption0">The Curious Tail of a Kite Balloon</div>
</div>
<div id="ip_160b" class="figright" style="width: 246px;">
<ANTIMG src="images/i_160b.jpg" width-obs="246" height-obs="335" alt="" /><br/>
<div class="captionl">British Official Photograph from Kadel & Herbert</div>
<div class="caption0">Observers in the Basket of an Observation-Balloon</div>
</div></div>
</div>
<h3>THE ZEPPELIN'S TINY ANTAGONISTS</h3>
<p>The one thing above all others that the Zeppelin
commander feared was the attack of airplanes.
In the early stages of the war, it was
considered unsafe for airplanes to fly by night
because of the difficulty of making a landing in
the dark. Later this difficulty was overcome by
the use of search-lights at the landing-fields.
The airplane would signal its desire to land and
the search-lights would point out the proper
landing-field for it. So that after the first few
months of the war Zeppelins were subjected to
the danger of airplane attack. Of course, on a
dark night it was very difficult for an airplane
to locate a Zeppelin, because the huge machine
could not be seen and the throb of its engines
was drowned out by the engines of the airplane<span class="pagenum"><SPAN name="Page_161" id="Page_161">161</SPAN></span>
itself. Nevertheless, Zeppelins were occasionally
located and destroyed by airplanes.</p>
<div id="ip_161" class="figcenter" style="width: 570px;">
<ANTIMG src="images/i_161.jpg" width-obs="570" height-obs="299" alt="" /><br/>
<div class="captionl">Photograph by Kadel & Herbert</div>
<div class="caption0">Enormous Range-finders mounted on a Gun Turret of an American Warship</div>
</div>
<p>The danger of the Zeppelin lay in the fact
that it was supported by an enormous volume
of very inflammable gas and the airplane needed
but to set fire to this gas to cause the destruction
of the giant of the air. And so the machine-guns
carried by airplanes were provided
with explosive, flaming bullets. A burst of
flame within the gas-bag would not set the gas
on fire, because there would be no air inside
to feed the fire, but surrounding the gas-bag
there was always a certain leakage of hydrogen
which would mix with the air in the compartment
and this would produce an explosive
mixture which needed but the touch of fire to
set it off. The Zeppelin was provided with a
ventilating-system to carry off these explosive
gases, but they could never be disposed of very
effectively, and, as a consequence, a number of
Zeppelins were destroyed by the tiny antagonists
that were sent up by the British and the
French. To fight off these assailants the Germans
provided their Zeppelins with guns which
would fire shrapnel shell. It is difficult for a
Zeppelin to use machine-guns against an airplane<span class="pagenum"><SPAN name="Page_162" id="Page_162">162</SPAN></span>
because the latter would merely climb
above the Zeppelin and would be shielded by
the balloon itself. And so the Germans put a
gun emplacement on top of the balloon both
forward and aft. There was a deck extending
along the top of the balloon which was reached
by a ladder running up through the center of
the airship. But it was impossible to ward off
the fleet little antagonists, once the dirigible was
discovered. True, a Zeppelin could make as
much as seventy miles per hour, but the fastest
airplanes could travel twice as fast as that.</p>
<h3>SUSPENDING AN OBSERVER BELOW THE ZEPPELIN</h3>
<p>One ingenious scheme that was tried was to
suspend an observation car under the Zeppelin.
The car was about fourteen feet long and five
feet in diameter, fitted with a tail to keep it
headed in the direction it was towed. It had
glass windows forward and there was plenty of
room in it for a man to lie at full length and
make observations of things below. The car
with its observer could be lowered a few thousand
feet below the Zeppelin, so that the observer
could watch proceedings below, while the
airship remained hidden among the clouds.<span class="pagenum"><SPAN name="Page_163" id="Page_163">163</SPAN></span>
The observer was connected by telephone with
the chart-room of the Zeppelin and could report
his discoveries or even act as a pilot to direct
the course of the ship.</p>
<p>But despite everything that could be done,
the Zeppelin eventually proved a failure as a
war-vessel because it was so very costly to construct
and operate and could so easily be destroyed,
and the Germans began to build huge
airplanes with which bombing-raids could be
continued.</p>
<p>Strange to say, however, although the Germans
were ready to admit the failure of their
big airship, when the war stopped the Allies
were actually building machines patterned after
the Zeppelin, but even larger, and expected to
use them for bombing-excursions over Germany.
This astonishing turn of the tables was
due to the fact that America had made a contribution
to aëronautics that solved the one
chief drawback of the Zeppelin.</p>
<h3>A BALLOON GAS THAT WILL NOT BURN</h3>
<p>When we entered the war against Germany,
our allies placed before us all their problems
and among them was this one of the highly inflammable<span class="pagenum"><SPAN name="Page_164" id="Page_164">164</SPAN></span>
airship. Could we not furnish a substitute
for hydrogen that would not burn? It
was suggested to us that helium would do if we
could produce that gas cheaply and in sufficient
quantity. Now, helium has a history of its own
that is exceedingly interesting.</p>
<p>Every now and then the moon bobs its head
into our light and we have a solar eclipse. But
our satellite is not big enough to cut off all
the light of the big luminary and the fiery atmosphere
of the sun shows us a brilliant halo
all around the black disk of the moon. Long
ago, astronomers analyzed this flaming atmosphere
with the spectroscope, and by the different
bands of light that appeared they were able
to determine what gases were present in the
sun's atmosphere. But there was one band of
bright yellow which they could not identify.
Evidently this was produced by a gas unknown
on earth, and they called it "helium" or "sun"
gas.</p>
<p>For a quarter of a century this sun gas remained
a mystery; then one day, in 1895, Sir
William Ramsay discovered the same band of
light when studying the spectrum of the mineral
cleveite. The fact that astronomers had been<span class="pagenum"><SPAN name="Page_165" id="Page_165">165</SPAN></span>
able to single out an element on the sun ninety
million miles away before our chemists could
find it right here on earth, produced a mild sensation,
but the general public attached no special
importance to the gas itself. It proved
to be a very light substance, next to hydrogen
the lightest of gases, and for years it resisted
all attempts at liquefaction. Only when Onnes,
the Dutch scientist, succeeded in getting it down
to a temperature of 450 degrees below zero, Fahrenheit,
did the gas yield to the chill and condense
into a liquid. The gas would not burn;
it would not combine with any other elements,
and apparently it had no use on earth, and it
might have remained indefinitely a lazy member
of the chemical fraternity had not the great
world conflict stirred us into frenzied activity
in all branches of science in our effort to beat
the Hun.</p>
<p>Because the gas had no commercial value,
there was only a small amount of helium to be
found in the whole world. Not a single laboratory
in the United States had more than five
cubic feet of it and its price ranged from
$1,500 to $6,000 per cubic foot. At the lowest
price it would cost $3,000,000,000 to provide gas<span class="pagenum"><SPAN name="Page_166" id="Page_166">166</SPAN></span>
enough for one airship of Zeppelin dimensions
and it seemed absurd even to think of a helium
airship.</p>
<h3>AMERICAN CHEMISTS TO THE RESCUE</h3>
<p>Just before the war it was discovered that
there is a considerable amount of helium in the
natural gas of Oklahoma, Texas, and Kansas,
and Sir William Ramsey suggested that our
chemists might study some method of getting
helium from this source. The only way of separating
it out was to liquefy the gases by subjecting
them to extreme cold. All gases turn
to liquid if they are cooled sufficiently, and then
further cold will freeze them solid. But helium
can stand more cold than any other and this
fact gave the clue to its recovery from natural
gas. The latter was frozen and one after
another the different elements condensed into
liquid, until finally only helium was left.
This sounds simple, but it is a difficult matter
to get such low temperature as that on a
large scale and do it economically. To be of
any real service in aëronautics helium would
have to be reduced in cost from fifteen hundred
dollars to less than ten cents per cubic<span class="pagenum"><SPAN name="Page_167" id="Page_167">167</SPAN></span>
foot. Several different kinds of refrigerating-machinery
were tried and finally just before the
war was brought to a close by the armistice we
had succeeded in producing helium at the rate
of eight cents per cubic foot, with the prospect
of reducing its cost still further. A large plant
for recovering helium was being built. The
plant will have been completed before this book
is published, and it will be turning out helium
for peaceful instead of military airships.</p>
<p>The reduction in the cost of helium is really
one of the most important developments of this
war. By removing the fire risk from airships
we can safely use these craft for aërial cruises
or for quick long-distance travel over land and
sea. For, even in time of peace, sailing under
millions of cubic feet of hydrogen is a serious
matter. Although no incendiary bullets are to
be feared, there is always the danger of setting
fire to the gas within the exhaust of the engines.
Engines have had to be hung in cars well below
the balloon proper. But with helium in the gas-bags
the engines can be placed inside the balloon
envelop and the propellers can operate on
the center line of the car.</p>
<p>In the case of one Zeppelin, the hydrogen was<span class="pagenum"><SPAN name="Page_168" id="Page_168">168</SPAN></span>
set on fire by an electric spark produced by friction
on the fabric of one of the gas-bags, and so
even with the engine exhausts properly screened
there is danger. The helium airship, however,
would be perfectly safe from fire and passengers
could smoke on deck or in their cabins
within the balloon itself without any more fear
of fire than they would have on shipboard.
Wonderful possibilities have been opened by the
production of helium on a large and economical
scale, and the airship seems destined to play
an important part in transportation very soon.
As this book is going to press, we learn of enormous
dirigibles about to be built in England for
passenger service, which will have half again as
great a lifting-power as the largest Zeppelins.
The final chapter of the story of dirigibles is yet
to be written, but in concluding this chapter it
is interesting to note that the world's greatest
aëronautic expert got his first inspiration from
America and finally that America has now furnished
the one element which was lacking to
make the dirigible balloon a real success.</p>
<hr />
<p><span class="pagenum"><SPAN name="Page_169" id="Page_169">169</SPAN></span></p>
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