[1] The remains of _Colymboides minutus_, from the Miocene of Langy,
described by this naturalist in the work just cited, seem to show it
to have been a generalized form. Unfortunately its tibia is unknown.
[2] A. H. Garrod, in his tentative and chiefly myological arrangement
of Birds (_Proc Zool. Society_, 1874, p. 117), placed the
_Colymbidae_ and _Podicipedidae_ in one order (_Anseriformes_) and
the _Alcidae_ in another (_Charadriiformes_); but the artificial
nature of this assignment may be realized by the fact of his
considering the other families of the former order to be _Anatidae_
and _Spheniscidae_.
[3] The osteology and myology of this species are described by Dr
Coues (_Mem. Boston Soc. Nat. History_, i. pp. 131-172, pl. 5).
[4] Lawrence's _C. pacificus_ seems hardly to deserve specific
recognition.
[5] In this connexion should be mentioned the remarkable occurrence
in Europe of two birds of this species which had been previously
wounded by a weapon presumably of transatlantic origin. One had "an
arrow headed with copper sticking through its neck," and was shot on
the Irish coast, as recorded by J. Vaughan Thompson (_Nat. Hist.
Ireland_, iii. p. 201); the other, says Herr H. C. Muller (_Vid.
Medd. nat. Forening_, 1862, p. 35), was found dead in Kalbaksfjord in
the Faeroes with an iron-tipped bone dart fast under its wing.
DIVERS and DIVING APPARATUS. To "dive" (Old Eng. _dufan_, _d['y]fan_;
cf. "dip") is to plunge under water, and in the ordinary procedure of
swimmers is distinguished from simple plunging in that it involves
remaining under the water for an interval of more or less duration
before coming to the surface. In the article SWIMMING the sport of
diving in this sense is considered. Here we are only concerned with
diving as the function of a "diver," whose business it is to go under
water (in modern times, assisted by specially devised apparatus) in
order to work.
_Unassisted or Natural Diving._--The earliest reference to the practice
of the art of diving for a purpose of utility occurs in the _Iliad_, 16,
745-750, where Patroclus compares the fall of Hector's charioteer to the
action of a diver diving for oysters. Thus it would seem that the art
was known about 1000 years before the Christian era. Thucydides is the
first to mention the employment of divers for mechanical work under
water. He relates that divers were employed during the siege of Syracuse
to saw down the barriers which had been constructed below the surface of
the water with the object of obstructing and damaging any Grecian war
vessels which might attempt to enter the harbour. At the siege of Tyre,
divers were ordered by Alexander the Great to impede or destroy the
submarine defences of the besieged as they were erected. The purpose of
these obstructions was analogous to that of the submarine mine of
to-day.
The employment of divers for the salvage of sunken property is first
mentioned by Livy, who records that in the reign of Perseus considerable
treasure was recovered from the sea. By a law of the Rhodians, their
divers were allowed a proportion of the value recovered, varying with
the risk incurred, or the depth from which the treasure was salved. For
instance, if the diver raised it from a depth of eight cubits (12 ft.)
he received one-third for himself; if from sixteen cubits (24 ft.) one
half; but upon goods lost near the shore, and recovered from a depth of
two cubits (36 in.), his share was only one tenth.
These are examples of unassisted diving as practised by the Ancients.
Their primitive method, however, is still in vogue in some parts of the
world--notably in the Ceylon pearl fisheries and in the Mediterranean
sponge fisheries, and it may, therefore, be as well to mention the
system adopted by the natural, or naked, diver of to-day.
The volume and power of respiration of the lungs vary in different
individuals, some persons being able to hold their breath longer than
others, so that it naturally follows that one man may be able to stay
longer under water than another. The longest time that a natural diver
has been known to remain beneath the surface is about two minutes. Some
pearl and sponge divers rub their bodies with oil, and put wool,
saturated with oil, in their ears. Others hold in their mouth a piece of
sponge soaked in oil, which they renew every time they descend. It is
doubtful, however, whether these expedients are beneficial. The men who
dive in this primitive fashion take with them a flat stone with a hole
in the centre; to this is attached a rope, which is secured to the
diving boat and serves to guide them to particular spots below. When the
diver reaches the sea bottom he tears off as much sponge within reach as
possible, or picks up pearl shells, as the case may be, and then pulls
the rope to indicate to the man in the boat that he wishes to be hauled
up. But so exhausting is the work, and so severe the strain on the
system, that, after a number of dives in deep water, the men often
become insensible, and blood sometimes bursts from nose, ears and mouth.
_Early Diving Appliances._--The earliest mention of any appliance for
assisting divers is by Aristotle, who says that divers are sometimes
provided with instruments for respiration through which they can draw
air from above the water and which thus enable them to remain a long
time under the sea (_De Part. Anim._ 2, 16), and also that divers
breathe by letting down a metallic vessel which does not get filled with
water but retains the air within it (_Problem._ 32, 5). It is also
recorded that Alexander the Great made a descent into the sea in a
machine called a _colimpha_, which had the power of keeping a man dry,
and at the same time of admitting light. Pliny also speaks of divers
engaged in the strategy of ancient warfare, who drew air through a tube,
one end of which they carried in their mouths, whilst the other end was
made to float on the surface of the water. Roger Bacon in 1240, too, is
supposed to have invented a contrivance for enabling men to work under
water; and in Vegetius's _De Re Militari_ (editions of 1511 and 1532,
the latter in the British Museum) is an engraving representing a diver
wearing a tight-fitting helmet to which is attached a long leathern pipe
leading to the surface, where its open end is kept afloat by means of a
bladder. This method of obtaining air during subaqueous operations was
probably suggested by the action of the elephant when swimming; the
animal instinctively elevates its trunk so that the end is above the
surface of the water, and thus is enabled to take in fresh air at every
inspiration.
A certain Repton invented "water armour" in the year 1617, but when
tried it was found to be useless. G. A. Borelli in the year 1679
invented an apparatus which enabled persons to go to a certain depth
under water, and he is credited with being the first to introduce means
of forcing air down to the diver. For this purpose he used a large pair
of bellows. John Lethbridge, a Devonshire man, in the year 1715
contrived "a watertight leather case for enclosing the person." This
leather case held about half a hogshead of air, and was so adapted as to
give free play to arms and legs, so that the wearer could walk on the
sea bottom, examine a sunken vessel and salve her cargo, returning to
the surface when his supply of air was getting exhausted. It is said
that Lethbridge made a considerable fortune by his invention. The next
contrivance worthy of mention, and most nearly resembling the modern
diving-dress, was an apparatus invented by Kleingert, of Breslau, in
1798. This consisted of an egg-ended metallic cylinder enveloping the
head and the body to the hips. The diver was encased first of all in a
leather jacket having tight-fitting arms, and in leather drawers with
tight-fitting legs. To these the cylinder was fastened in such a way as
to render the whole equipment airtight. The air supply was drawn through
a pipe which was connected with the mouth of the diver by an ivory
mouthpiece, the surface end being held above water after the manner
mentioned in Vegetius, viz. by means of a floating bladder attached to
it. The foul air escaped through another pipe held in a similar manner
above the surface of the water, inhalation being performed by the mouth
and exhalation by the nose, the act of inhalation causing the chest to
expand and so to expel the vitiated air through the escape pipe. The
diver was weighted when going under water, and when he wished to ascend
he released one of his weights, and attached it to a rope which he held,
and it was afterwards hauled up.
_Modern Apparatus._--This, or equally cumbersome apparatus, was the
only diving gear in use up till 1819, in which year Augustus Siebe (the
founder of the firm of Siebe, Gorman & Co.), invented his "open" dress,
worked in conjunction with an air force pump. This dress consisted of a
metal helmet and shoulder-plate attached to a watertight jacket, under
which, fitting more closely to the body, were worn trousers, or rather a
combination suit reaching to the armpits. The helmet was fitted with an
air inlet valve, to which one end of a flexible tube was attached, the
other end being connected at the surface with a pump which supplied the
diver with a constant stream of fresh air. The air, which kept the water
well down, forced its way between the jacket and the under-garment, and
escaped to the surface on exactly the same principle as that of the
diving bell; hence the term "open" as applied to this dress.
Although most excellent work was accomplished with this dress--work
which could not be attempted before its introduction--it was still far
from perfect. It was absolutely necessary for the diver to maintain an
upright, or but very slightly stooping, position whilst under water; if
he stumbled and fell, the water filled his dress, and, unless quickly
brought to the surface, he was in danger of being drowned. To overcome
this and other defects, Siebe carried out a large number of experiments
extending over several years, which culminated, in the year 1830, in the
introduction of his "close" dress in combination with a helmet fitted
with air inlet and regulating outlet valves.
Though, of course, vast improvements have been introduced since Siebe's
death, in 1872, the fact remains that his principle is in universal use
to this day. The submarine work which it has been instrumental in
accomplishing is incalculable. But some idea of the importance of the
invention may be gathered from the fact that diving apparatus on Siebe's
principle is universally used to-day in harbour, dock, pier and
breakwater construction, in the pearl and sponge fisheries, in
recovering sunken ships, cargo and treasure, and that every ship in the
British navy and in most foreign navies carries one set or more of
diving apparatus.
A modern set of diving apparatus consists essentially of six parts:--(1)
an air pump, (2) a helmet with breastplate, (3) a diving dress, (4) a
pair of heavily weighted boots, (5) a pair of back and chest weights,
(6) a flexible non-collapsible air tube.
[Illustration: FIG. 1.--Pump out of chest.
Two-cylinder, Double-action Air Pump for Two Divers.
A, Air-distributing arrangement, for one diver or two divers.
B, Water jacket.
C, Suction and discharge valves.
D, Cylinders.
E, Pressure gauges.
F, Nozzles to which divers' air pipes are attached.]
_Air Pumps._--The type of air pump varies with the depth of water to
which the diver has to descend; it will be readily understood that the
greater the depth the greater the quantity of air required by the
diver. The pattern most generally in favour amongst divers of all
classes is a three-cylinder single-acting pump, which is suitable for
almost every description of work which the diver may be called upon to
perform, either in deep or shallow water. Another most useful type is
a two-cylinder double-acting pump (figs. 1 and 2), which is designed
to supply two divers working simultaneously in moderate depths of
water, or one diver only in deep water. An air-distributing
arrangement is fitted, whereby, when it is desired to send two men
down together, each cylinder supplies air independently of the other;
and when it is required to send one diver into deep water, the two
cylinders are connected and the full volume of air from both is
delivered to the one man. The same duty is also performed by a
four-cylinder single-acting pump. Smaller pumps, having one
double-acting or two single-acting cylinders, are also used for
shallow water work.
In most cases these air pumps are worked by manual power; this method
of working is rendered necessary by the fact that the machines are
usually placed in small boats from which the divers work and on which
other motive power is not available. In cases, however, where steam or
electric power is available the pumps are sometimes worked by their
means--more particularly on harbour and dock works. In such instances
the air is not delivered direct from the pump to the diver, but is
delivered into an intermediate steel receiver to which the diver's air
pipe is connected, the object being to ensure a reserve supply of air
in case of a breakdown of the pump. Some of these combinations of
pumps and motors are so arranged that, in the event of an accident to
the motor, the pump can be thrown out of gear with it, and be
immediately worked by hand power. Each pump is fitted with a gauge (or
gauges), indicating not only the pressure of air which the pump is
supplying, but also the depth of water at which the diver is working.
The cylinders are water-jacketed to ensure the air delivered to the
diver being cool, the water being drawn in and circulated round the
cylinders by means of a small metal pump worked from an eccentric on
the main crank-shaft. Filters are sometimes attached to the suction
and delivery sides of the pumps to ensure the inlet of air being free
from dirt, and the discharge of air free from dirt and oil.
[Illustration: FIG. 2.--Pump in chest, ready for work.]
_Helmet._--The helmet and breastplate (fig. 3) are made from highly
planished tinned copper, with gun-metal valves and other fittings. The
helmet is provided with a non-return air inlet valve to which the
diver's air pipe is connected; the air when it lifts the inlet valve
passes through three conduits--one having its outlet over the front
glass, the others their outlets over the side glasses. In this way the
diver gets the air fresh as it enters the helmet, and at the same time
it prevents condensation of his breath on the glasses and keeps them
clear. There is a regulating air outlet valve by which the diver
adjusts his supply of air according to his requirements in different
depths of water; the valve is usually made to be adjusted by hand, but
sometimes it is so constructed as to be operated by the diver knocking
his head against it, the spindle being extended through to the inside
of the helmet and fitted at its inner extremity with a button or disk.
By unscrewing the valve, the diver allows air to escape, and thus the
dress is deflated; by screwing it up the air is retained and the dress
inflated. Thus the diver can control his specific gravity and rise or
sink at will. In case by any chance the diver should inflate the dress
inadvertently, and wish to get rid of the superfluous air quickly, he
can do so by opening an emergency cock, which is fitted on the helmet.
Plate glasses in gun-metal frames are also fitted to the helmet, two,
one on each side, being permanently fixed, while one in front is made
either to screw in and out, or to work on a hinged joint like a ship's
scuttle; the side glasses are usually protected by metal cross-bars,
as is also sometimes the front glass. Some divers prefer unprotected
glasses at the side of the helmet, instead of protected oval ones.
The breastplate is fitted on its outer edge with metal screws and
bands. The disposition of the screws corresponds with that of the
holes in the india-rubber collar of the diving dress described below.
There are other methods of making a watertight joint between the
diver's breastplate and the diving dress, but, as these are only
mechanical differences, it will suffice to describe the Siebe-Gorman
apparatus, as exclusively adopted by the British government. Whatever
the shape or design of the helmet or dress, Siebe's principle is the
one in universal use to-day.
The metal tabs are for carrying the diver's lead weights, which are
fitted with suitable clips; the hooks--one on each side of the
helmet--are for keeping the ropes attached to the back weight in
position. The helmet and breastplate are fitted at their lower and
upper parts respectively with gun-metal segmental neck rings, which
make it possible to connect these two main parts together by
one-eighth of a turn, a catch at the back of the helmet preventing any
chance of unscrewing. The small eyes at the top of the helmet are for
securing the diver's air pipe and life line in position and preventing
them from swaying.
[Illustration:
Front view of Helmet.
A, Helmet.
B, Breastplate.
F, Emergency cock.
G, Glasses in frames.
H, Metal screws and bands.
I, Metal tabs.
J, Hooks for keeping weight ropes in position.
L, Eyes to which air pipe and life line are secured.
Side sectional view of Helmet.
K, Segmental neck rings.
D, Air conduits.
M, Telephone receiver.
N, Transmitter.
O, Contact piece to ring bell.
Back view of Helmet.
Plan of Helmet.
C, Air inlet valve.
E, Regulating outlet valve.
G, Glasses in frames.
L, Eyes to which air pipe and life line are secured.
P, Connexion for telephone cable.