THE MECHANISM OF DIVING
Diving being a profession which can be carried on in its simplest form
with the simplest possible apparatus--merely a rope and a stone--its
history reaches back into the dim and inexplorable past. We may well
believe that the first man who explored the depths of the sea for
treasure lived as long ago as the first seeker for minerals in the
bosom of the earth. Even when we come to the various appliances which
have been gradually developed in the course of centuries, our records
are very imperfect. Alexander the Great is said to have descended in a
machine which kept him dry, while he sought for fresh worlds to conquer
below the waves. Aristotle mentions a device enabling men to remain
some time under water. This is all the information, and a very meagre
total, too, that we get from classical times.
Stepping across 1,500 years we reach the thirteenth century, about the
middle of which Roger Bacon is said to have invented the diving-bell.
But like some other discoveries attributed to that Middle-Age
physicist, the authenticity of this rests on very slender foundations.
In a book published early in the sixteenth century there appears an
illustration of a diver wearing a cap or helmet, to which is attached
a leather tube floated on the surface of the water by an inflated
bag. This is evidently the diving dress in its crudest form; and
when we read how, in 1538, two Greeks made a submarine trip under a
huge inverted chamber, which kept them dry, in the presence of the
great Emperor Charles V. and some 12,000 spectators, we recognise the
diving-bell, now so well known.
The latter device did not reach a really practical form till 1717,
when Dr. Halley, a member of the Royal Society, built a bell of wood
lined with lead. The divers were supplied with air by having casks-full
lowered to them as required. To quote his own words: "To supply air to
this bell under water, I caused a couple of barrels of about thirty
gallons each to be cased with lead, so as to sink empty, each of them
having a bunghole in its lowest parts to let in the water, as the air
in them condensed on their descent, and to let it out again when they
were drawn up full from below. And to a hole in the uppermost parts
of these barrels I fixed a leathern hose, long enough to fall below
the bunghole, being kept down by a weight appended, so that the air
in the upper parts of the barrels could not escape, unless the lower
ends of these hose were first lifted up. The air-barrels being thus
prepared, I fitted them with tackle proper to make them rise and fall
alternately, after the manner of two buckets in a well; and in their
descent they were directed by lines fastened to the under edge of the
bell, which passed through rings on both sides of the leathern hose in
each barrel, so that, sliding down by these lines, they came readily to
the hand of a man, who stood on purpose to receive them, and to take
up the ends of the hose into the bell. Through these hose, as soon as
their ends came above the surface of the water in the barrels, all the
air that was included in the upper parts of them was blown with great
force into the bell, whilst the water entered at the bungholes below
and filled them, and as soon as the air of one barrel had been thus
received, upon a signal given that was drawn up, and at the same time
the other descended, and by an alternate succession, provided air so
quick and in such plenty that I myself have been one of five who have
been together at the bottom, in nine to ten fathoms water, for above
an hour and a half at a time, without any sort of ill-consequence, and
I might have continued there so long as I pleased for anything that
appeared to the contrary." After referring to the fact that, when the
sea was clear and the sun shining, he could see to read or write in the
submerged bell, thanks to a glass window in it, the Doctor goes on to
say: "This I take to be an invention applicable to various uses, such
as fishing for pearls, diving for coral or sponges and the like, in
far greater depths than has hitherto been thought possible; also for
the fitting and placing of the foundations of moles, bridges, etc., in
rocky bottoms, and for cleaning and scrubbing ships' bottoms when foul,
in calm weather at sea. I shall only intimate that, _by an additional
contrivance_, I have found it not impracticable for a diver to go out
of an engine to a good distance from it, the air being conveyed to him
with a continued stream by small flexible pipes, which pipes may serve
as a clue to direct him back again when he would return to the bell."
We have italicised certain words to draw attention to the fact that
Dr. Halley had invented not only the diving bell, but also the diving
dress. Though he foresaw practically all the uses to which diving
mechanism could be put, the absence of a means for forcing air _under
pressure_ into the bell or dress greatly limited the utility of his
contrivances, since the deeper they sank below the water the further
would the latter rise inside them. It was left for John Smeaton, of
Eddystone Lighthouse fame, to introduce the _air-pump_ as an auxiliary,
which, by making the pressure of the air inside the bell equal to
that of the water outside, kept the bell quite free of water. Smeaton
replaced Halley's tub by a square, solid cast-iron box, 50 cwt. in
weight, large enough to accommodate two men at a time. The modern bell
is merely an enlarged edition of this type, furnished with telephones,
electric lamps, and, in some cases, with a special air-lock, into which
the men may pass when the bell is raised. The pressure in the air-lock
is very gradually decreased after the bell has reached the surface,
if work has been conducted at great depths, so that the evil effects
sometimes attending a sudden change of pressure on the body may be
avoided.
Diving bells are very useful for laying submarine masonry, usually
consisting of huge stone blocks set in hydraulic cement. Helmet divers
explore and prepare the surface on which the blocks are to be placed.
Then the bell, slung either from a crane on the masonry already built
above water-level, or from a specially fitted barge, comes into action.
The block is lowered by its own crane on to the bottom. The bell
descends upon it and the crew seize it with tackle suspended inside the
bell. Instructions are sent up as to the direction in which the bell
should be moved with its burden, and as soon as the exact spot has been
reached the signal for lowering is given, and the stone settles on to
the cement laid ready for it.
The modern diver is not sent out from a bell, but has his separate
and independent apparatus. The first practical diving helmet was that
of Kleingert, a German. This enclosed the diver as far as the waist,
and constituted a small diving bell, since the bottom was open for
the escape of vitiated air. Twenty years later, or just a century
after the invention of Halley's bell, Augustus Siebe, the founder of
the present great London firm of Siebe, Gorman, and Company, produced
a more convenient "open" dress, consisting of a copper helmet and
shoulder-plate in one piece, attached to a waterproof jacket reaching
to the hips.
The disadvantage of the open dress was, that the diver had to maintain
an almost upright position, or the water would have invaded his helmet.
Mr. Siebe therefore added a necessary improvement, and extended the
dress to the feet, giving his diver a "close" protection from the water.
We may pass over the gradual development of the "close" dress and
glance at the most up-to-date equipment in which the "toilers of the
deep" explore the bed of Old Ocean.
The dress--legging, body, and sleeves--is all in one piece, with a
large-enough opening at the shoulders for the body to pass through. The
helmet, with front and side windows, is attached by a "bayonet joint"
to the shoulder-plate, itself made fast to the upper edge of the
dress by screws which press a metal ring against the lower edge of the
plate so as to pinch the edge of the dress.
[Illustration:
_Photo Cribb._
THE DIVER AT WORK
Note the telephone attachment, the wires of which are embedded in the
life-line held by the bluejacket on the left. By means of the telephone
the diver can give and receive full instructions about his work.]
At the back are an inlet and an outlet valve. Between the front and a
side window is the transmitter of a loud-sounding telephone, and in the
crown the receiver and the button of an electric bell. The telephone
wires, and also the wires for a powerful electric light, working on
a ball-and-socket joint in front of the dress, are embedded into the
life-line. The air-tube, of canvas and rubber, has a stiffening of wire
to prevent its being throttled on coming into contact with any object.
A pair of weighted boots, each scaling 17 lbs., two 40-lb. lead weights
slung over the shoulder, and a knife worn at the waist-belt, complete
the outfit of the diver, which, not including the several layers of
underclothing necessary to exclude the cold found at great depths,
totals nearly 140 lbs. Of this the copper helmet accounts for 36 lbs.
On the surface are the air-pumps, which may be of several
types--single-cylinder, double-acting; double-cylinder, double-acting;
or three or four cylinder, single-acting--according to the nature of
the work. All patterns are so constructed that the valves may be easily
removed and examined.
The pressure on a diver increases in the ratio of about 4-1/4 lbs. for
every ten feet he descends below the surface. A novice experiences
severe pains in the ears and eyes at a few fathoms' depth, which,
however, pass off when the pressures both inside and outside of the
various organs have become equalised. On rising to the surface again
the pains recur, since the external pressure on the body falls more
quickly than the internal. The rule for all divers, therefore, is
"slow down, slow up." Men of good constitution and resourcefulness are
needed for the profession of diving. Only a few can work at extreme
depths, though an old hand is able to remain for several hours at a
time in sixty feet of water. The record depth reached by a diver is
claimed by James Hooper, who, when removing the cargo of the _Cape
Horn_, wrecked off the coast of South America, made seven descents to
201 feet, one of which lasted forty-two minutes.
In spite of the dangers and inconveniences attached to his calling, the
diver finds in it compensations, and even fascinations, which outweigh
its disadvantages. The pay is good--£1 to £2 a day--and in deep-sea
salvage he often gets a substantial percentage of all the treasure
recovered, the percentage rising as the depth increases. Thus the diver
Alexander Lambert, who performed some plucky feats during the driving
of the Severn Tunnel,[18] received £4,000 for the recovery of £70,000
worth of gold from the _Alphonso XII._, sunk off Grand Canary. Divers
Ridyard and Penk recovered £50,000 from the _Hamilla Mitchell_, which
lay in 160 feet of water off Shanghai, after nearly being captured
by Chinese pirates; and we could add many other instances in which
treasure has been rescued from the maw of the sea.
The most useful sphere for a diver is undoubtedly connected with
the harbour work and the cleaning of ships' bottoms. For the latter
purpose every large warship in the British Navy carries at least one
diver. After ships have been long in the water barnacles and marine
growths accumulate on the below-water plates in such quantities as
to seriously diminish the ship's speed, which means a great waste of
fuel, and would entail a loss of efficiency in case of war breaking
out. Armed with the proper tools, a gang of divers will soon clean the
"foul bottom," at a much smaller cost of time and money than would be
incurred by dry-docking the vessel.
The Navy has at Portsmouth, Sheerness, and Devonport schools where
diving is taught to picked men, the depth in which they work being
gradually increased to 120 feet. Messrs. Siebe and Gorman employ
hundreds of divers in all parts of the world, on all kinds of submarine
work, and they are able to boast that never has a defect in their
apparatus been responsible for a single death. This is due both to the
very careful tests to which every article is subjected before it leaves
their works, and also to the thorough training given to their employés.
In the sponge and pearl-fishing industries the diving dress is
gradually ousting the unaided powers of the naked diver. One man
equipped with a standard dress can do the work of twenty natural
divers, and do it more efficiently, as he can pick and choose his
material.
This chapter may conclude with a reference to the apparatus now used
in exploring or rescue work in mines, where deadly fumes have overcome
the miners. It consists of an air-tight mask connected by tubes to a
chamber full of oxygen and to a bag containing materials which absorb
the carbonic acid of exhaled air. The wearer uses the same air over and
over again, and is able to remain independent of the outer atmosphere
for more than an hour. The apparatus is also useful for firemen when
they have to pass through thick smoke.
FOOTNOTE:
[18] Vide _The Romance of Modern Engineering_, p. 212.