~HOW SHOOTING SHELLS ARE PHOTOGRAPHED~
One of the most progressive branches of our military service is the
Department of Coast Defenses, which, under the far-seeing guidance of
General E. M. Weaver, holds our shores and harbors in a state of alert
preparedness against foreign aggression. At Hampton Roads sits the
Coast Artillery Board, composed of officers and consulting engineers
to whom are referred all problems relating to coast artillery, and who
have the responsibility of testing all new instruments proposed for
artillery use. The purpose of this article is to describe one among
several notable achievements of the Hampton Roads Coast Artillery
School, this particular work having been done by Captain F. J. Behr of
the Coast Artillery Corps, who, after years of effort, has recently
developed a system that makes it possible to take pictures of the
swiftest moving bodies, the great steel projectiles of our biggest
guns--to seize them with the camera’s eye as they hurl through the air
at enormous velocities or at the very moment of their emergence from
the gun muzzles, and to preserve these images, never seen before, for
military study and comparison. Captain Behr was ably assisted in this
work by Engineer J. A. Wilson.
[Illustration: THE FASTEST CAMERA IN THE WORLD
The big gun, equipped with the fastest camera shutter in the world,
about to be fired and the shell photographed.
For years a young officer of the Coast Artillery has been trying to
devise a camera so incredibly swift that it will record every stage of
this lightning flight from the gun-barrel to the target. At last he has
succeeded. His photographs--some of them taken one hundred thousandth
of a second apart--have revealed remarkable and unsuspected facts to
the military world. The story of his invention had never before been
told.]
Reckoning in Millionths of a Second.
Some of the increments and decrements of time involved in the series of
photographs herewith published (several of them for the first time) are
as small as one ten-thousandth part of a second. And Captain Behr has
devised a method of taking photographs of projectiles as they arrive at
a steel target and penetrate the target, inch by inch, that involves
increments or decrements of time as small as the one hundred-thousandth
part of a second. To the uninitiated it seems incredible that such
infinitesimal divisions of time can be used in practical calculations;
but every trained physicist knows that in wireless work scientists of
to-day speak casually of experiments that take account of _two-tenths
or one-tenth of a millionth part of a second_!
[Illustration: THE PROJECTILE EMERGING FROM MORTAR
In this photograph--the first of a remarkable series showing five
stages of a moving projectile--the half-ton projectile seems to be
standing still, but really it is traveling at the rate of 900 miles an
hour. The gunners here work in concrete pits 34 feet high. Underneath
the mounts are the powder magazines. Each pit has four mortars usually
served by an entire Coast Artillery Company. The projectiles are the
same as those used in the twelve-inch guns, but less powder is required
because mortar projectiles are hurled high in the air, not straight at
a vessel, and deliver their destructive blows downward from a great
height.]
[Illustration: THE SMOKE RINGS WHICH APPEAR
This second photograph shows the projectile almost entirely out of the
mortar. Its sharp nose may be seen above the “gas-ring” forming at its
upper end. These “gas-rings,” or “smoke-rings,” come without warning,
and only occasionally, perhaps once in eight or ten shots. They rise
swiftly to the height of fifty or a hundred feet, growing larger
and larger, and giving forth a weird, shrieking sound like a second
projectile. Some insist that these “smoke-rings” are as hard as steel,
owing to the enormous compression of their composing gases, and the
story is told of a bird caught in the path of one of them and torn to
pieces.]
What happened to the projectile after it leaves the gun, or after
the discharge of the gun, and before the projectile has had time to
issue from the gun-barrel? What is the action at the muzzle of gases
generated? What shape do these gases assume as they leave the gun? What
causes the much-discussed “gas-rings” that sometimes form when a mortar
is fired, and oftener do not form? What phenomena attend the arrival
of the projectile at a solid steel target? Is the steel actually fused
by the heat of impact? Is it vaporized? Or what? These are some of
the questions that Captain Behr set himself to solve, or to help in
solving, as he worked out his methods of rapid photography. His aims
were strictly military, but his results make fascinating appeal to the
general imagination. Fancy doing anything in the one hundred-thousandth
part of a second!
[Illustration: THE PROJECTILE HIDDEN BY THE SMOKE CONE
In the third photograph the smoke-cone is almost perfect and gives the
famous “powder-puff” effect. It still hides the projectile, although
the latter is traveling at a velocity that would take it from New York
to Chicago in one hour. At night the “gas-rings” present a startling
and fascinating appearance, burning with a reddish orange glow, and
whirling with a complicated double motion, strange opalescent balls,
like rings of Saturn. A study of these photographs--the first record
ever made of the “gas-rings”--has led some experts to the conclusion
that the cause of the rings is defective ramming of the projectile.]
[Illustration: THE PROJECTILE EMERGING FROM SMOKE CONE
The fourth photograph shows the projectile emerging from the smoke-cone
about thirty feet above the muzzle of the mortar. The men who fire
these mortars from the mortar-pits never see the distant target or
vessel they are firing at, but point their mortars according to
directions transmitted to them (usually by telephone) from observers at
distant stations. And so great a degree of precision has been attained
that, on certain practice occasions at Hampton Roads, a record of nine
hits out of ten shots has been scored on a moving target five miles out
in the ocean. This picture shows the smoke-cone as first seen by the
human eye.]
Captain Behr’s general idea was to utilize some phenomena connected
with the discharge to actuate, by electrical connections, a mechanism
that would work a rapid shutter in a properly placed camera. The
phenomenon of concussion was tried first--the smash of air against a
little swinging door; but this was much too slow. The projectile was
hundreds of yards away before the camera had registered its picture.
And that chance was gone!
[Illustration: THE PROJECTILE HIGH IN THE AIR
In the fifth photograph the projectile is seen entirely clear of the
smoke-cone and well started on its long flight. Climbing into the sky
at this steep angle, it will reach a height of from three to six miles
before it begins to descend. There are harbors on our coasts guarded by
so many guns and mortars that if these were fired simultaneously they
could hurl against a given small area a converging rain of projectiles
aggregating more than fifty tons in their combined mass. A minute later
they could hurl another fifty tons against the same small area; and so
on as long as the ammunition lasted.]
In the next trial, several months later, Captain Behr arranged to
have the electrical connections made or broken by the movement of the
gun-carriage itself in recoiling; but the result was unsatisfactory.
Nor was he more fortunate at the succeeding target practice, when,
having placed the apparatus farther forward on the parapet, he had the
camera demolished by the force of the concussion and several blades of
the rapid shutter broken. He was satisfied, now, that his effort to
actuate the camera mechanism from the gun-carriage would never give the
requisite precision in results, and he saw that he must work with a
device functioning more reliably.
In the months that followed before the next target practice, the
Captain did some experimenting, and finally determined making the
projectile itself displace a length of piano-wire fixed across the
muzzle of the gun, and thus actuate the electrical system and operate
the shutter. In this way he eliminated troublesome variables of
recoil, elasticity of the carriage, etc., leaving to determine only
the time element of the electrical system to function. This result was
admirable, and, after taking several similar pictures, the captain
found that he could now operate with great precision--that is, he could
get the same phase of the discharge with almost identical shapes of
gas-cone and smoke-cloud, and he could get these every time.
In the fall of 1912 Captain Behr succeeded in obtaining a series of
extremely rapid photographs showing a twelve-inch mortar battery in
action. In taking these pictures the camera was placed on an elevation
about ten feet above the concrete floor and about sixty feet back of
the mortars. The electrical device for working the shutter was actuated
by the mortar itself in its recoil. These pictures were taken in about
one five-thousandth of a second--which is the more remarkable as the
last two were taken in the shade after 4.30 A.M. The first three were
taken about noon, in the sunshine, as the shadows show.
So great was the precision of the electrical device as to render
possible the photographic recording of these mortar projectiles,
moving at great velocities, in almost any desired position after the
discharge, say two feet away from the muzzle, or six feet away, or
twenty feet away, or right at the muzzle, as shown in the first mortar
picture, where the great projectile has been caught in its flight half
way out of the mortar.
Pictures Never Seen By the Human Eye.
~A CAMERA THAT IS FASTER THAN THE EYE~
It is interesting to note that of these five mortar pictures,
representing five phases of the firing, only the last two are ever
seen by the human eye. The far swifter camera, acting in about one
five-thousandth of a second, has caught all these phases as reproduced
here; but, to the ordinary observer standing by, the first visible
impression after firing is that of the smoke-cone as developed in
Number Four. The strange “powder-puff” effect shown in Number Three is
never seen; nor the earlier effects in Numbers One and Two. Nor is any
sound heard by an observer or by the gun crew until the third or fourth
phase has been reached. This is a matter of simple calculation.
Sound travels through the air very slowly as compared with light, and
in Numbers One, Two, and Three, although the crashing explosion has
taken place and the projectile is already started on its long journey,
the men (even the lanyard man, who is nearest), have heard nothing,
since the sound-waves have not yet had time to reach their ears. Nor
has the mortar itself had time to recoil, as it does presently, down
into the well in the floor of the pit.
The men aboard the towing vessels that drag the floating targets during
gun and mortar practice would seem to be in a dangerous position, since
the tow-line is not more than two hundred yards long for guns and
five hundred yards long for mortars, and a very slight error in aim
or adjustment might cause a deviation of several hundred yards when
the range is eight or ten thousand yards. As a matter of fact, such
errors do not occur, and a gun-pointer who would make a right or left
deviation from the target of ten yards, or at the most fifteen yards
at a distance of five miles, would be considered unfit for his job.
In one or two rare instances a towing vessel has been struck when a
projectile has fallen short and then ricochetted to the right, as it
invariably does owing to its rotation in that direction. The rifling of
the gun-barrel causes this rotation.
[Illustration: This shows one of Captain Behr’s earliest efforts to
photograph the projectile from a twelve-inch gun. The man on the
platform has been adjusting the electrical connections that actuate
the camera mechanism. The halo effect at the muzzle of the gun is due
to compressed air caused by the forward rush of the projectile. The
projectile has not yet emerged from the muzzle of the gun. On the right
is the place where the “Merrimac” and the “Monitor” had their famous
fight.]
Sometimes these great projectiles ricochet several times, and go
bounding over the water as a pebble skips along the surface of a
mill-pond, only there may be the distance of a mile or more between
these giant leaps.
The Projectile Travels Faster Than the Sound It Makes.
A strange phenomenon is witnessed by the observer on a towing vessel as
he looks, rather uneasily perhaps, toward the distant shore battery,
that seems to be firing straight at him. First there is a flash and
a puff of smoke; then nothing for a period of seconds, while the
projectile is on its way; then suddenly a great splash as the mass of
iron strikes the water. Up to this moment there has been no sound of
the discharge, no sound of the projectile, since it travels faster than
the sound-waves; but now, _after_ it has buried itself in the ocean, is
heard its own unmistakable voice, a low, buzzing _um-m-m-m_ approaching
from the shore. The projectile itself has arrived _before_ the sound
that it makes in transit, and the sound arrives afterward. Last of all
is heard the boom of the discharge.
[Illustration: A GUN THAT PHOTOGRAPHED ITS OWN SHOT
In this beautiful picture the hurling projectile was itself the
photographer: that is, in passing out of the gun-barrel, it broke a
length of piano-wire stretched across the muzzle and thus automatically
closed an electrical circuit that actuated the camera mechanism. And so
rapid was the shutter that the great shot hurled forth in the discharge
photographed here has not yet had time to issue from the smoke-cone,
where it is still hidden.]
Owing to the great velocity of gun projectiles, it is almost impossible
for an observer near the target to see them as they approach; but a
trained eye can discern the slower moving mortar projectiles as they
drop out of the sky, shrieking as they come, curving downward from a
height of four or five miles, half a ton falling from a height of four
or five miles.
[Illustration: EXPLODING A SUBMARINE MINE
This photograph illustrates another important form of coast
defense--the submarine mine. A target about 5 by 5 feet, with a red
flag at its apex, is towed across the mine-field, the mines being
exploded electrically from a shore station several miles away. The
methods of laying and exploding these mines are carefully kept secrets.
In this case a charge of five hundred pounds of the newest explosive
was used. Fragments of the shattered target and mine-buoy are seen at
the right of the picture. Tons of water are hurled into the air by
these explosions, and hundreds of fish are killed or stunned.]
It is difficult to realize what an enormous force is released when one
of these twelve-inch guns is discharged. The pressure inside of the
gun behind the projectile is between thirty-five and forty thousand
pounds to the square inch. No engine or machine made by man produces
anything like this pressure. The boiler pressure in steam-engines,
or in big turbines driven by superheated steam, does not exceed two
hundred or three hundred pounds to the square inch. The huge hydraulic
presses that would crumple up a steel girder do not exert a pressure
of more than one thousand pounds to the square inch. The only reason
a gun-barrel can resist this pressure (forty thousand pounds to the
square inch) is that it is built up in a series of concentric steel
hoops or tubes shrunk one over the other until there is a resistance
capacity of from seventy thousand to ninety thousand pounds to the
square inch. Even at rest, the barrels of these great guns are under
such enormous compression, from being thus squeezed within these outer
steel coverings, that, if the retaining steel jackets were suddenly
cut, the tubes would blow themselves into pieces from the violent
reaction of release.
Not only does this smokeless powder, burning inside these guns,
produce enormous pressure, but it generates inconceivably great heat.
Water boils at 100° Centigrade; iron melts at 1400°; platinum and
the most resistant metals at 2900°; while the hottest thing on earth
is the temperature of the electric arc, in which carbon boils. This
temperature is between 3000° and 4000° Centigrade, and is believed to
be the same as that of these great powder chambers when the gun is
fired. Thus a diamond, the hardest substance known, would melt in the
barrel of a twelve-inch gun at the moment of discharge. The consequence
is that at each discharge of a big gun a thin skin of metal inside
the barrel is literally fused, and this leads to rapid erosion of
the softened surfaces under the tearing pressure of gases generated.
The rifling is worn away; the band over the projectile becomes
loose-fitting; and soon the huge gun, that has cost such a great sum,
is rendered unfit for service. The life of a twelve-inch gun is only
450 rounds, that is, the gun would be worn out if fired every three
minutes for a single day. After that a new life may be given it by
boring out the inner tube and putting in a new steel lining.
A Secret for Which Foreign Governments Would Pay Millions.
A few words may be added about the formidable smokeless powder used in
these great guns. This powder, in spite of its terrible power, is of
innocent appearance, and a small stick of it may be held safely in the
hand while it burns with a vivid yellowish flame. There is no danger
of its exploding or detonating like gun-cotton, and yet it is made
from gun-cotton, treated by a colloiding process that is one of our
jealously guarded military secrets. There are foreign governments that
would give millions to know exactly how this powder is made and how it
is preserved for years without deterioration. The recent destruction of
two ships of the French navy was due, it is believed, to deterioration
of their smokeless powder.
[Illustration]
Why Do Some Eyes In a Picture Seem to Follow Us?
If a person’s picture is taken with the eyes of the person looking
directly into the lens or opening of the camera, then the eyes in
the picture will always be directly on and appear to follow whoever
is looking at it. This is also true of paintings. If a subject being
painted is posed so as to look directly at the painter, and the artist
paints the picture with the eyes so pointed, then the eyes of the
picture will follow you. When you are looking at a picture of a person
and the eyes do not follow you, you will know at once that he was not
looking at the camera or artist when the picture was being taken or
painted.
[Illustration]
Where Does a Light Go When It Goes Out?
~WHY YOU CAN BLOW OUT A CANDLE~
To understand the answer to this question fully you will first have to
learn what light is, and particularly that it is not the flame from
the gas jet or of the lamp or candle that is actually the light, but
that light consists of rays or waves in the ether, which is constantly
in all space and even in our bodies, coming from the something that
is burning. This in the instance above mentioned would be the gas
burning as it comes out of the gas jet, the oil in the lamp as it comes
up through the wick or the flame of the candle. We are apt to call
a lighted gas jet a lamp, or a candle, light, because it is steady.
Really, however, there is no such thing as keeping light in a room in
an actual sense, for rays of light travel from the substance which
produces them faster than anything else we know of in the world. The
first thing a light wave does when it is once created is to go some
place, and it does this at the rate of 186,000 miles per second. If it
cannot penetrate the walls of the room it is either reflected back in
the direction from which it came or transformed by the objects which it
strikes into some other kind of energy.
When you look at the rays coming from a gas jet, you do not see one ray
for more than, say the millionth part of a second, but because these
rays of light come so fast one after the other from the burning jet and
spread in all directions, they seem to be continuous.
So you see that the rays of light are going away as fast as they are
coming from the gas jet. They either go on as light or, as said above,
are changed into other forms of energy when they strike things they
cannot penetrate in the form of light, or rather one thing, which is
heat. A large part of it goes into the air in the room in the form of
heat, as you well know, now that it is called to your attention. Some
of it goes into the furniture and some of it is changed into another
form of heat, which, combining with the chemicals in other things it
mixes with, changes their appearance and usefulness. As, for instance,
the carpets and hangings in the room, the colors of which become faded
when exposed to light rays too much. The heat from the light rays is
responsible for the fading of colors in our garments as well.
When you “put out the light,” as we say, or turn off the gas, you cut
off the source of light. Really, then, our expression that “the light
goes out” is only true while the gas is lighted, for from the flaming
gas jet the light is going out all the time, whereas when the gas is
turned off no light is being produced, and when you turn off the gas
you do not turn out the light, but only that which makes light.
Why Does a Fire Go Out?
Fire will go out naturally when there is nothing left to burn, or it
will go out if it cannot secure enough oxygen out of the air to keep it
going. In the first case it dies what we might call a “natural death,”
and in the latter case the fire practically suffocates. The fire in
the open fireplace, if it has plenty of air, will burn up everything
burnable that it can reach. The stones of the fireplace or other parts
of a stove will not burn, because they have already been burned, and
you cannot burn anything a second time, if all of the oxygen in it was
burned out of it the first time.
Now, then, to burn up a thing, you must first start a fire under it,
and then keep a constant draft of air playing on it from beneath, or
the fire will die out. The more difficult a thing is to burn, the more
important it is that you have plenty of draft. If the ashes accumulate
under the fire the air cannot go through them in sufficient quantity
and the fire will go out. Other things which prevent the current of air
from going up through the fire will cause it to go out. That is why we
close the lower door of the furnace, to keep the fire from burning out.
When we shut off the draft of air from below, the fire in the furnace
burns slowly, i. e., it just hangs on, so to speak.
Why Does a Lamp Give a Better Light With the Chimney On?
When a lamp is burning without a chimney it generally smokes. That
is because the oil which is coming up through the wick is being only
partially burned. The carbon, which is about one-half of what the oil
contains, is not being burned at all, and goes off into the air in
little black specks with the gases which are thrown off. The reason
the carbon is not burned when the chimney is off is that there is not
sufficient oxygen from the air combining with it, as it is separated
from the oil in the partial combustion that is going on. To make the
carbon in the oil burn you must mix it with plenty of oxygen at a
certain temperature, and this can only be done by forcing sufficient
oxygen through the flame to bring the heat of the flame to the point
where the carbon will combine with it and burn. When you put the
chimney on the lamp you create a draft which forces more oxygen through
the flame, brings the heat up to the proper temperature and enables the
carbon to combine with it and burn. When you take the chimney off again
the heat goes down, when the draft is shut off and the lamp smokes
again.
The chimney also protects the flame of the lamp from drafts from the
sides and above, and helps to make a brighter light, because a steady
light is brighter than a flickering one.
The draft created by the chimney also forces the gases produced by the
burning oil up and away from the flame. Some of these gases have a
tendency to put out a light or a fire.
Does Light Weigh Anything?
To get at the answer to this question we must go back to the definition
of light. Light is a wave in the ether and contains no particles of
matter. It, therefore, does not weigh anything at all.
When men had studied light thoroughly, however, they came to the
conclusion that it must have the power of pressure, which, from the
standpoint of results, would amount to the same thing as having weight.
They reasoned that if you had a perfect balance and let sunlight shine
down on one of the sides of the balance, that side should go down under
the pressure of light. In their first experiments along this line men
failed to show that under such conditions the side of the balance on
which the light shone did go down, but by continuous experiments it was
proved finally that the light did exert a sufficient pressure to cause
the scales to go down, and in effect this is the same as having weight;
but this has been found to be a common property of rays of various
kinds, including heat, and we, therefore, do not speak of this quality
as weight, but as the power of radiating pressure.
Why Does a Stick Seem to Bend When Put in Water?
When light passes from one medium to another, as for example from glass
or water to air, or from air or glass to water, the rays of light
change their course, thus making them seem to be bent or broken. The
rays of light from the part of the stick in the water take a different
direction from the rays from the part which is out of the water, giving
the appearance of breaking or bending at the place where the air and
water meet. It is, of course, the light rays which are bent and not the
object itself.
This bending or changing of the path of light rays is called
refraction. If you place a coin in a glass of water so that it may be
viewed obliquely, you can apparently see two coins, a small one through
the surface of the water and another apparently magnified through the
side of the glass.
This is due only to the absolute principle that rays of light change
their direction in passing from one thing to another, and on this
principle of the rays of light our optical instruments, including the
microscope, the telescope, the camera and eyeglasses are based.
What Makes the Stars Twinkle?
I might tell you, just to show how clever I am, that stars do not
twinkle at all, and leave you with that for an answer. But since they
really do seem to twinkle, and that is what causes your question,
I will tell you. As we have already learned in our talks about the
stars and the sky in general, the stars are suns which are constantly
throwing off light, just as our sun gives us light, and when this light
strikes the air which surrounds the earth it meets many objects--little
particles of dust and other things always floating about in it. The
light comes to us in the form of rays from the stars and some of
these rays strike particles of various kinds in the air and are thus
interfered with. If you are looking at a lighted window some distance
away and there are a lot of boys and girls or men and women running
past the window, one after the other, rapidly, it will make the
light in the window appear to twinkle. The twinkling is due to the
interference which the rays of light encounter while traveling toward
the eye.
Why Does an Onion Make the Tears Come?
That is nature’s way of protecting the eyes from the smarting which the
onion would cause in your eyes if the tears did not come quickly and
overcome the bad effect so produced. Tears are provided for washing the
ball of your eyes. Every time you wink a little tear is released from
under the eyelid, and the wink spreads it all over the eyeball. This
washes down the front of the eyeball and cleanses it of all dust and
other things that fly at the eye from the air. Then the tear runs along
a little channel, much like a trough, at the lower part of the eye,
and out through a little hole in the eye, and in this case the tear is
really only an eye-wash. Many things, but more often sadness or injured
feelings, start the tears coming so fast from under the eyelid that the
little trough at the bottom and the hole in the corner of the eye are
too small to hold them or carry them off, so they roll over the edge of
the lower eyelid and down the face. These are what we call tears. Among
other things that will cause tear-glands to cause an over-supply of
eye-wash to come down, are onions. What they give off is very trying to
the eyes, and so, just as soon as the something which an onion throws
off hits the eyeball, the nerves of the eye telegraph the brain to turn
on the tears quickly, and they come in a little deluge and counteract
the bad effect of the onion.
[Illustration: SOME REMARKABLE PICTURES WITH A FAST CAMERA]
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[Illustration: THE CAVE MAN OF PREHISTORIC TIMES WHO UNCONSCIOUSLY
INVENTED AMMUNITION]