Chapter X: Act 1890 (4)

[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.

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.

_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.

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.

FIG. 3.]

The _Diving Dress_ is a combination suit which envelops the whole body
from feet to neck. It is made of two layers of tanned twill with pure
rubber between, and is fitted at the neck with a vulcanized
india-rubber collar, or band, with holes punched in it corresponding
to the screws in the breastplate. This collar, when clamped tightly
between the bands and the breastplate by means of the nuts, ensures a
watertight joint. The sleeves of the dress are fitted with vulcanized
india-rubber cuffs, which, fitting tightly round the diver's wrists,
prevent the ingress of water at these parts also.

_Boots._--These are generally made with leather uppers, beechwood
inner soles and leaden outer soles, the latter being secured to the
others by copper rivets. Heavy leather straps with brass buckles
secure the boot to the foot. Each boot weighs about 16 lb. Sometimes
the main part of the boot-golosh, toe and heel, are in one brass
casting, with leather upper part, heavy straps and brass buckles.

_Lead Weights._--These weigh 40 lb. each, and the diver wears one on
his back, another on his chest. These weights and the heavy boots
ensure the diver's equilibrium when under water.

_Belt and Knife and Small Tools._--Every diver wears a heavy
waist-belt in which he carries a strong knife in metal case, and
sometimes other small tools.

_Air Pipe._--The diver's air pipe is of a flexible, non-collapsible
description, being made of alternate layers of strong canvas and
vulcanized india-rubber, with steel or hard drawn metal wire embedded.
At the ends are fitted gun-metal couplings, for connecting the pipe
with the diver's pump and helmet.

_Signal Line._--The diver's signal line (sometimes called life line)
consists of a length of reverse laid Manila rope. In cases where the
telephone apparatus is not used, the diver gives his signals by means
of a series of pulls on the signal line in accordance with a
prearranged code.

Q, Battery, with switch and bell in case.
R, Attendant's receiver and transmitter.]

_Telephonic Apparatus._--Without doubt one of the most useful adjuncts
to the modern diving apparatus is the loud-sounding telephone (fig.
4), introduced by Siebe, Gorman & Co., which enables the diver to
communicate viva voce with his attendant, and vice versa. In the
British navy the type of submarine telephonic apparatus used is the
Graham-Davis system. This is made on two plans, (1) a single set of
instruments, for communication between one diver and his attendant
direct, (2) an intercommunication set which is used where two divers
are employed. With this type the attendant can speak to No. 1 or No. 2
diver separately, or with both at the same time, and vice versa; and
No. 1 can be put in communication with No. 2 whilst they are under
water, the attendant at the surface being able to hear what the men
are saying. The advantages of such a system are obvious. It is more
particularly useful where two divers are working one either side of a
ship, or where the divers may be engaged upon the same piece of work,
but out of sight of one another, or out of touch. It would prove its
utility in a marked degree in cases where a diver got into
difficulties; a second diver sent down to his assistance could receive
and give verbal directions and thus greatly expedite the work of
rescue.

The telephone instruments in the helmet consist of one or more
loud-sounding receivers placed either in the crown of the helmet, or
one on each side in close proximity to the diver's ears. A transmitter
of a special watertight pattern is placed between the front glass and
one of the side glasses, and a contact piece, which, when the diver
presses his chin against it, rings a bell at the surface, is fitted
immediately below the front glass. A buzzer is sometimes fixed in the
helmet to call the diver's attention when the attendant wishes to
speak, but as a rule the voice is transmitted so loudly that this
device is unnecessary. A connexion, through which the insulated wires
connecting the instruments pass, terminates in contact pieces, and the
telephone cable, embedded in the diver's signal line, is connected
with it. The other end of the signal line is connected to a battery
box at the surface. This box contains, besides the cells, a receiver
and transmitter for the attendant, an electric bell, a terminal box,
and a special switch, by means of which various communications between
diver, or divers, and attendant are made. If, as is sometimes the
case, the diver happens to be somewhat deaf, he can, whilst he is
taking a message, stop the vibration of the outlet valve and the noise
made by the escaping air, by merely pressing his finger on a spindle
which passes through the disk of the valve, and thus momentarily
ensure absolute silence.

_Speaking Tube._--The rubber speaking tube which was the forerunner of
the telephonic apparatus is now practically obsolete, though it is
still used in isolated cases.

_Submarine Electric Lamps._--Various forms of submarine lamps are
used, from a powerful arc light to a self-contained hand lamp, the
former giving about 2000 or 3000 candle-power, and requiring a
steam-driven dynamo to supply the necessary current, the latter (fig.
5) giving a light of about 10 candle-power and having its own
batteries, so that the diver carries both the light and its source in
his hand. These submarine lamps are all constructed on the same
principle, having the incandescent lamps, or carbons as the case may
be, enclosed in a strong glass globe, the mechanism and connexions
being fitted in a metal case above the globe, which is flanged and
secured watertightly to the case.

_Self-contained Diving Dress._--The object of the self-contained diving
dress is to make the diver independent of air supply from the surface.
The dress, helmet, boots and weights are of the ordinary pattern
already described, but instead of obtaining his air supply by means of
pumps and pipes, the diver is equipped with a knapsack consisting of a
steel cylinder containing oxygen compressed to a pressure of 120
atmospheres (= about 1800 lb.) to the square inch, and chambers
containing caustic soda or caustic potash. The helmet is connected to
the chambers by tubes, and the oxygen cylinder is similarly connected
to the chambers. The breath exhaled by the diver passes through a
valve into the caustic soda, which absorbs the carbonic acid, and it
is then again inhaled through another valve. This process of
regeneration goes on automatically, the requisite amount of oxygen
being restored to the breathed air in its passage through the
chambers. This type of apparatus has been used for shallow water work,
but the great majority of divers prefer the apparatus using pumps as
the source of the air supply.

An emergency dress, using this self-contained system for breathing,
has been designed by Messrs Fleuss and Davis, of the firm of Siebe,
Gorman & Co., primarily as a life-saving apparatus, for enabling men
to escape from disabled submarine boats.

The helmet diver is indispensable in connexion with harbour and dock
construction, bridge-building, pearl and sponge fishing, wreck raising
and the recovery of sunken cargo and treasure. Every ship in the
British navy carries one set or more of diving apparatus, for use in
ease of emergency, for clearing fouled propellers, cleaning valves or
ship's hull below the water line, repairing hulls if necessary, and
recovering lost anchors, chains, torpedoes, &c.

A, Metal case containing electrical fittings.
B, Glass globe and incandescent lamp.
C, Stand, which also protects the globe.
D, Ring for suspending lamp.
E, Reflector.]

_Greatest Depths attained._--The greatest depth at which useful work has been performed by a diver is 182 ft. From this depth a Spanish diver, Angel Erostarbe, recovered L9000 in silver bars from the wreck of the steamer "Skyro," sunk off Cape Finisterre; Alexander Lambert succeeded in salving L70,000 from the Spanish mail steamer "Alphonso XII," sunk in 162 ft. of water off Las Palmas, Grand Canary; W. Ridyard recovered L50,000 in silver dollars from the "Hamilton Mitchell," sunk off Leuconna Reef, China, in 150 ft. There are individual cases where much larger sums have been recovered, but those mentioned are particularly notable by reason of the great depth involved and stand out as the greatest depths at which good work has been done. The sponge fishers of the Mediterranean work at a maximum depth of about 150 ft., and the pearl divers of Australia at 120 ft. But submarine operations on the great majority of the harbour and dock works of the world are conducted at a depth of from 30 to 60 ft.

The weighted tools employed by divers differ very little from those used by the workmen on _terra firma_. Pneumatic tools, worked by compressed air conveyed from the surface through flexible tubes, are great aids, particularly in rock removal work. With the rock drill the diver bores a number of holes to a given depth, inserts in these the charges of dynamite or other explosive used, attaches one end of a wire to a detonator which is inserted in the charge, and then comes to the surface. The boat from which he works is then moved away from the scene of operations, paying out the wire attached to the detonators, and when at a safe distance the free end of the wire is connected to a magneto exploding machine, which is then set in motion.

A complete set of diving apparatus costs from L75 to L200, varying with the depth of water for which it is required.

The pay of a diver depends upon the nature of the work upon which he is engaged, and also upon the depth of the water. On harbour and dock work the average wage is 2s. to 2s. 6d. per hour; on wreck work from 3s. to 5s. an hour, according to depth; on treasure and cargo recovery so much per day, with a percentage on the value recovered, generally about 5%. The pearl fishers of Australia get so much per ton of shell, and the sponge fishers are also paid by results.

A problem which has been exercising the minds of those engaged in submarine work is the greatest depth at which it is possible to work, for, as is well known, many a fine vessel with valuable cargo and treasure is lying out of reach of the diver owing to the pressure which he would have to sustain were he to attempt to reach her. Mr Leonard Hill, and Drs Greenwood and J. J. R. Macleod conducted experiments in conjunction with Messrs Siebe, Gorman & Co., with a view to solving this problem, and their efforts have been attended with some considerable success. Dr J. S. Haldane has also carried out practical experiments for the British Admiralty, and under his supervision two naval officers have succeeded in reaching the unprecedented depth of 210 ft., at which depth the pressure is about 90 lb. to the square inch.

_Diving Bells._--Every one is familiar with the experiment of placing an inverted tumbler in a bowl of water, and seeing the water excluded from the tumbler by the air inside it. Perhaps it was to some such experiment as this that the conception of the diving bell was due. As is well known, the pressure of water increases with the depth, and for all practical purposes this pressure can be taken at 4-1/4 lb. to every 10 ft. The following table shows the pressure at different depths below the surface of the water:--

Depth. Pressure.

20 ft. 8-1/2 lb to the sq. in.
40 " 17-1/4 " "
80 " 34-3/4 " "
120 " 52-1/2 " "
160 " 69-3/4 " "
200 " 87 " "

If a diving bell be sunk to a depth of, say, 33 ft., the air inside it will be compressed to about half its original volume, and the bell itself will be about half filled with water. But if a supply of air be maintained at a pressure equal to the depth of water at which the bell is submerged, not only will the water be kept down to the cutting edge, but the bell will be ventilated and it will be possible for its occupants to work for hours at a stretch.

Tradition gives Roger Bacon, in 1250, the credit for being the originator of the diving bell, but actual records are lost in antiquity. Of the records preserved to us, probably one of the most trustworthy is an account given in Kaspar Schott's work, _Technica curiosa_, published in the year 1664, which quoted from one John Taisnier, who was in the service of Charles V. This account describes an experiment which took place at Toledo, Spain, in the year 1538, before the emperor and some thousands of spectators, when two Greeks descended into the water in a large "kettle," suspended by ropes, with its mouth downwards. The "kettle" was equipoised by lead fixed round its mouth. The men came up dry, and a lighted candle, which they had taken down with them, was still burning.

Francis Bacon, in the _Novum Organum_, lib. ii., makes the following reference to a machine, or reservoir, of air to which labourers upon wrecks might resort whenever they required to take breath:--

"A hollow vessel, made of metal, was let down equally to the surface
of the water, and thus carried with it to the bottom of the sea the
whole of the air which it contained. It stood upon three feet--like a
tripod--which were in length something less than the height of a man,
so that the diver, when he was no longer able to contain his breath,
could put his head into the vessel, and having filled his lungs again,
return to his work."

But it was to Dr Edmund Halley, secretary of the Royal Society, that undoubtedly the honour is due of having invented the first really practical diving bell. This is described in the _Philosophical Transactions_, 1717, in a paper on "The Art of Living Under Water by means of furnishing air at the bottom of the sea in any ordinary depth." Halley's bell was constructed of wood, and was covered with lead, which gave it the necessary sinking weight, and was so distributed as to ensure that it kept a perpendicular position when in the water. It was in the form of a truncated cone, 3 ft. in diameter at the top, 5 ft. at the bottom and 8 ft. high. In the roof a lens was introduced for admitting light, and also a tap to let out the vitiated air. Fresh air was supplied to the bell by means of two lead-lined barrels, each having a bung-hole in the top and bottom. To the hole in the top was fixed a leathern tube, weighted in such a manner that it always fell below the level of the bottom of the barrel so that no air could escape. When, however, the tube was turned up by the attendant in the bell, the pressure of the water rising through the hole in the bottom of the barrel, forced the air through the tube at the top and into the diving bell. These barrels were raised and lowered alternately, with such success that Halley says that he, with four others, remained at the bottom of the sea, at a depth of 9 to 10 fathoms, for an hour and a half at a time without inconvenience of any sort.

This type of bell was used by John Smeaton in repairing the foundations of Hexham Bridge in 1778, but instead of weighted barrels, he introduced a force pump for supplying the necessary air. To Smeaton too we are indebted for the first diving bell plant in the form with which we are familiar to-day, that celebrated engineer having designed a square bell of iron, for use on the Ramsgate harbour works, in 1788. This bell, which measured 4-1/2 ft. in length, 3 ft. in width and 4-1/2 ft. in height, and weighed 2-1/2 tons, was made sufficiently heavy to sink by its own weight. It afforded room enough for two men to work, and was supplied with air by a force pump worked from a boat at the surface.

Though the diving bell has been largely superseded by the modern diving apparatus, it is still used on certain classes of work the magnitude of which justifies the expense entailed, for it is not only a question of the cost of the bell, but of the powerful steam-driven crane which is needed to lower and raise it, and also of the gantry on which the crane travels. Sometimes a barge or other vessel is used for working the bell.

At the present day, two types of diving bell are employed--the ordinary bell, and the air-lock bell, which, however, is not so largely used.

On the new national harbour works at Dover, four large diving bells of
the ordinary type (fig. 6) were employed. These bells, in each of
which from four to six men descended at a time, consisted of steel
chambers, open at the bottom, measuring 17 ft. long by 10-1/2 ft. wide by
7 ft. high, and each weighed 35 tons. The ballast, which at once gives
the necessary sinking weight to the bell and maintains its
equilibrium, consisted of slabs of cast iron bolted to the walls of
the bell, inside. Each bell was fitted with loud-sounding telephonic
apparatus, by means of which the occupants could communicate either
with the men attending the crane or the men looking after the air
compressors at the surface. Electric lamps, supplied with current by a
dynamo in the compressor room, gave the necessary light inside the
bell. Seats and foot rails were provided for the men, and there were
racks and hooks for the various tools. Suspended from the roof was an
iron skip into which the men threw the excavated material, which was
emptied out when the bell was brought to the surface. Air was supplied
to the bells by means of steam-driven compressors worked in a house
erected on the gantry. The air was delivered into a steel air
receiver, and thence it passed through a flexible tube connected to a
gun-metal inlet valve in the roof of the diving bell; the pressure of
air was regulated according to the depth at which the bell happened to
be working. The maximum depth on the Dover works was between 60 and 70
ft., = about 25-30 lb. to the square inch. A bell was lowered by
means of powerful steam-driven cranes, travelling on a gantry, to
within a few feet of the water, and the men entered it from a boat.
The bell then continued its descent to the bottom, where the men, with
pick and shovel, levelled the sea bed ready to receive the large
concrete blocks, weighing from 30 to 42 tons apiece. Having completed
one section, the bell was moved along to another. The concrete blocks
were then lowered and placed in position by helmet divers. The bell
divers, clad in thick woollen suits and watertight thigh boots, worked
in shifts of about three hours each, and were paid at the rate of from
1s. to 15d. per hour.

A, Working chamber.
B, Air-lock.
C, Pulleys and wire ropes for lowering and raising bell.
D, Iron ladder.
E, Tackles suspended from roof for raising and lowering objects.
F, Air supply pipe.]

The cost of an ordinary diving bell, including air compressor,
telephonic apparatus and electric light, is from L600 to L1500,
according to size.

The _Air-lock Diving Bell_ (fig. 7) comprises an iron or steel working
chamber similar to the ordinary diving bell, but with the addition of
a shaft attached to its roof. At the upper end of the shaft is an
airtight door, and about 8 ft. below this is another similar door.
When the bell divers wish to enter the bell, they pass through the
first door and close it after them, and then open a cock or valve and
gradually let into the space between the two doors compressed air from
the working chamber in order to equalize the pressure; they then open
the second door and pass down into the working chamber, closing the
door after them. When returning to the surface they reverse the
operation. It can readily be imagined that, owing to its unwieldy
character, the employment of the air-lock bell is resorted to only in
those cases where the nature of the sea bed necessitates its remaining
on a given spot for some considerable time, as for instance in the
excavation of hard rock to a given depth.

An air-lock bell supplied to the British Admiralty, for use in
connexion with the laying of moorings at Gibraltar, has a working
chamber measuring 15 ft. long by 10-1/2 ft. wide, by 7-1/2 ft. high,
and a shaft 37-1/2 ft. high by 3 ft. in diameter. It is built of steel
plates, with cast-iron ballast, and its total weight is about 46 tons.
The bell is electrically lighted, and is fitted with telephonic
apparatus communicating with the air-compressor room and lifting-winch
room. It is worked through a well in the centre of a specially
constructed steel barge 85 ft. long by 40 ft. beam, having a draught
of 7 ft. 6 in. The wire ropes, for lowering and raising the bell, work
over pulleys which are carried on a superstructure erected over the
well. Two sets of air compressors are fitted on the barge--one set for
supplying air to the bell, the other set for working a pneumatic rock
drill inside the bell. The greatest depth at which this particular
bell will work is 40 ft. The cost of the whole plant, including barge,
was about L14,000.

The diving dress has, however, to a great extent supplanted the diving
bell. This is due not only to the heavier cost of the latter, but more
particularly to the greater mobility of the helmet diver. Bell divers
are naturally limited to the area which their bell for the time being
covers, whereas helmet divers can be distributed over different parts
of a contract and work entirely independently of one another. The use
of the diving bell is, therefore, practically limited to the work of
levelling the sea bed, and the removal of rock.

See also the article CAISSON DISEASE as regards the physiological
effects of compressed air. (R. H. D.*)

DIVES-SUR-MER, a small port and seaside resort of north-western France on the coast of the department of Calvados, on the Dives, 15 m. N.E. of Caen by road. Pop. (1906) 3286. Dives is celebrated as the harbour whence William the Conqueror sailed to England in 1066. In the porch of its church (14th and 15th centuries) a tablet records the names of some of his companions. The town has a picturesque inn, adapted from a building dating partly from the 16th century, and market buildings dating from the 14th to the 16th centuries. The coast in the vicinity of Dives is fringed with small watering-places, those of Cabourg (to the west) and of Beuzeval and Houlgate (to the east) being practically united with it. There are large metallurgical works with electric motive power close to the town.

DIVIDE, a word used technically as a noun in America and the British colonies for any high ridge between two valleys, forming a water-parting; a dividing range. For special senses of the verb "to divide" (Lat. _di-videre_, the latter part of the word coming from a root seen in Lat. _vidua_, Eng. "widow"), meaning generally to split up in two or more parts, see DIVISION. In a parliamentary sense, to divide (involving a separation into two sides, Aye and No) is to take the sense of the House by voting on the subject before it.

DIVIDEND (Lat. _dividendum_, a thing to be divided), the net profit periodically divisible among the proprietors of a joint-stock company in proportion to their respective holdings of its capital. Dividend is not interest, although the word dividend is frequently applied to payments of interest; and a failure to pay dividends to shareholders does not, like a failure to pay interest on borrowed money, lay a company open to being declared bankrupt. In bankruptcy a dividend is the proportionate share of the proceeds of the debtor's estate received by a creditor. In England, the Companies Act 1862 provided that no dividend should be payable except out of the profits arising from the business of the company, but, in the case of companies incorporated by special act of parliament for the construction of railways and other public works which cannot be completed for a considerable time, it is sometimes provided that interest may during construction be paid to the subscribers for shares out of capital. Dividends (excluding occasional distributions in the form of shares) are ordinarily payable in cash. Most companies divide their capital into at least two classes, called "preference" shares and "ordinary" shares, of which the former are entitled out of the profits of the company to a preferential dividend at a fixed rate, and the latter to whatever remains after payment of the preferential dividend and any fixed charges. Before, however, a dividend is paid, a part of the profits is often carried to a "reserve fund." The dividend on preference shares is either "cumulative" or contingent on the profits of each separate year or half year. When cumulative, if the profits of any one year are insufficient to pay it in full, the deficiency has to be made good out of subsequent profits. A cumulative preferential dividend is sometimes said to be "guaranteed," and preferential dividends payable by all English companies registered under the Companies Acts 1862 to 1908 are cumulative unless stipulated to be otherwise. Certain public companies are forbidden by parliament to pay dividends in excess of a prescribed maximum rate, but this restriction has been happily modified in some instances, notably in the case of gas companies, by the institution of a sliding scale, under which a gas company may so regulate the price of gas to be charged to consumers that any reduction of an authorized standard price entitles the company to make a proportionate increase of the authorized dividend, and any increase above the standard price involves a proportionate decrease of dividend. Dividends are usually declared yearly or half-yearly; and before any dividend can be paid it is, as a rule, necessary for the directors to submit to the shareholders, at a general meeting called for the purpose, the accounts of the company, with a report by the directors on its position and their recommendation as to the rate of the proposed dividend. The articles of association of a company usually provide that the shareholders may accept the director's recommendation as to dividend or may declare a lower one, but may not declare a higher one than the directors recommend. Directors frequently have power to pay on account of the dividend for the year, without consulting the shareholders, an "interim dividend," which on ordinary shares is generally at a much lower rate than the final or regular dividend. An exceptionally high dividend is often distributed in the shape of a dividend at the usual rate supplemented by an additional dividend or "bonus." Payment of dividends is made by means of cheques sent by post, called "dividend warrants." All dividends are subject to income-tax, and by most companies dividends are paid "less income-tax," in which case the tax is deducted from the amount of dividend payable to each proprietor. When paid without such deduction a dividend is said to be "free of income-tax." In the latter case, however, the company has to make provision for payment of the tax before declaring the dividend, and the amount of its divisible profits and the rate of dividend which it is able to declare are consequently to that extent reduced. In respect of consols and certain other securities, holders of amounts of less than L1000 may instruct the Bank of England or Bank of Ireland to receive and invest their dividends. With few exceptions, the prices of securities dealt in on the London Stock Exchange include any accruing dividend not paid up to the date of purchase. At a certain day, after the dividend is declared, the stock or share is dealt in on the Stock Exchange, as _ex dividend_ (or "x. d."), which means that the current dividend is paid not to the buyer but to the previous holder, and the price of the stock is lower to that extent. The expression "cum dividend" is used to signify that the price of the security dealt in includes a dividend which, in the absence of any stipulation, might be supposed to belong to the seller of the security. On the New York Stock Exchange the invariable practice is to sell stock with the "dividend on" until the company's books are closed, after which it is usually sold "ex dividend." (S. D. H.)

DIVIDIVI, the native and commercial name for the astringent pods of _Caesalpinia coriaria_, a leguminous shrub of the suborder _Caesalpinieae_, which grows in low marshy tracts in the West Indies and the north of South America. The plant is between 20 and 30 ft. in height, and bears white flowers. The pods are flattened, and curl up in drying; they are about 3/4 in. broad, from 2 to 3 in. long and of a rich brown colour. Dividivi was first brought to Europe from Caracas in 1768. It contains about 30% of ellagitannic acid, whence its value in leather manufacture.

DIVINATION, the process of obtaining knowledge of secret or future things by means of oracles, omens or astrology. The root of the word, _deus_ (god) or _divus_, indicates the supposed source of the soothsayer's information, just as the equivalent Greek term, [Greek: mantike], indicates the spiritual source of the utterances of the seer, [Greek: mantis]. In classical times the view was, in fact, general, as may be seen by Cicero's _De divinatione_, that not only oracles but also omens were signs sent by the gods; even the astrologer held that he gained his information, in the last resort, from the same source. On the side of the Stoics it was argued that if divination was a real art, there must be gods who gave it to mankind; against this it was argued that signs of future events may be given without any god.

Divination is practised in all grades of culture; its votaries range from the Australian black to the American medium. There is no general agreement as to the source of the information; commonly it is held that it comes from the gods directly or indirectly. In the Bornean cult of the hawk it seems that the divine bird itself was regarded as having a foreknowledge of the future. Later it is regarded as no more than a messenger. Among the Australian blacks, divination is largely employed to discover the cause of death, where it is assumed to be due to magic; in some cases the spirit of the dead man is held to give the information, in others the living magician is the source of the knowledge. We find moreover a semi-scientific conception of the basis of divination; the whole of nature is linked together; just as the variations in the height of a column of mercury serve to foretell the weather, so the flight of birds or behaviour of cattle may help to prognosticate its changes; for the uncultured it is merely a step to the assumption that animals know things which are hidden from man. Haruspication, or the inspection of entrails, was justified on similar grounds, and in the case of omens from birds or animals, no less than in astrology, it was held that the facts from which inferences were drawn were themselves in part the causes of the events which they foretold, thus fortifying the belief in the possibility of divination.

From a psychological point of view divinatory methods may be classified under two main heads: (A) autoscopic, which depend simply on some change in the consciousness of the soothsayer; (B) heteroscopic, in which he looks outside himself for guidance and perhaps infers rather than divines in the proper sense.

(A) Autoscopic methods depend on (i.) sensory or (ii.) motor automatisms, or (iii.) mental impressions, for their results. (i.) Crystal-gazing (q.v.) is a world-wide method of divining, which is analogous to dreams, save that the vision is voluntarily initiated, though little, if at all, under the control of the scryer. Corresponding to crystal-gazing we have _shell-hearing_ and similar methods, which are, however, less common; in these the information is gained by hearing a voice. (ii.) The divining rod (q.v.) is the best-known example of this class; divination depending on automatic movements of this sort is found at all stages of culture; in Australia it is used to detect the magician who has caused the death of a native; in medieval and modern times water-divining or _dowsing_ has been largely and successfully used. Similar in principle is _coscinomancy_, or divining by a sieve held suspended, which gives indications by turning; and the equally common divination by a suspended ring, both of which are found from Europe in the west to China and Japan in the east. The ordeal by the Bible and key is equally popular; the book is suspended by a key tied in with its wards between the leaves and supported on two persons' fingers, and the whole turns round when the name of the guilty person is mentioned. Confined to higher cultures on the other hand, for obvious reasons, is divination by automatic writing, which is practised in China more especially. The sand divination so widely spread in Africa seems to be of a different nature. _Trance speaking_, on the other hand, may be found in any stage of culture and there is no doubt that in many cases the procedure of the magician or shaman induces a state of auto-hypnotism; at a higher stage these utterances are termed oracles and are believed to be the result of inspiration (q.v.). (iii.) Another method of divination is by the aid of mental impressions; observation seems to show that by some process of this sort, akin to clairvoyance (q.v.), fortunes are told successfully by means of palmistry or by laying the cards; for the same "lie" of the cards may be diversely interpreted to meet different cases. In other cases the impression is involuntary or less consciously sought, as in dreams (q.v.), which, however, are sometimes induced, for purposes of divination, by the process known as incubation or temple sleep. Dreams are sometimes regarded as visits to or from gods or the souls of the dead, sometimes as signs to be interpreted symbolically by means of dream-books, which are found not only in Europe but in less cultured countries like Siam.