DIVING. 
the fishing for pearls, corals-, • sponges, &c. 
See Pearl-fishing, &c. 
Various methods have been proposed, and 
engines contrived, to render the business of 
diving more safe and easy. The great point 
in ail these is to furnish the diver with fresh 
air, without which he must either make but 
a short stay, or perish. 
Those who dive for sponges in the Medi- 
terranean, help themselves by carrying down 
sponges dipt in oil in their mouths/ But con- 
sidering the small quantity of air that can be 
contained in the pores of a sponge, and how 
much that little will be contracted by the 
pressure of the incumbent water, such a sup- 
ply cannot long subsist the diver. For it is 
found by experiment that a gallon of air in- 
cluded in a bladder, and by a pipe recipro- 
cally inspired and expired by the lungs, be- 
comes unfit for respiration in little more than 
one minute of time. For though its elasticity 
is but little altered in passing the lungs, yet 
it loses its oxygen, and is rendered 'ef- 
fete. In effect, a naked diver, Dr. Halley 
assures us, without a sponge, cannot remain 
above two minutes inclosed in water ; nor 
much longer with one without suffocating ; 
nor without long practice near so long, ordi- 
nary persons beginning to be suffocated in 
about half a minute. Besides, if the depth 
is considerable, the pressure of the water on 
the vessels makes the eyes blood-sho'ten, and 
frequently occasions a spitting of blood. 
Hence where there has been occasion to con- 
tinue long at the bottom, some have con- 
trived double flexible pipes, to circulate air 
down into a cavity inclosing the diver, as 
with armour, both to furnish air, and to bear 
off the pressure of the water, and give leave 
to his breast to dilate upon inspiration : the 
fresh air being forced down one of the pipes 
with bellows, and returning by the other, 
not unlike to an artery and vein. 
But this method is impracticable when the 
depth surpasses three fathoms ; the water 
embracing the bare limbs so closely as to 
obstruct the circulation of the blood in them ; 
and also pressing so strongly on all the junc- 
tures where the armour is made tight with 
leather, that, if there is the least defect in 
any of them, the water rushes in, and in- 
stantly fills the whole engine, to the great 
danger of the diver’s life. 
It is said to be a fact, that people, by be- 
ing accustomed to the water from their in- 
fancy, will at length he enabled, not only to 
stay much longer under water than could be 
supposed, but put on a kind of amphibious 
nature, so that they seem to have the use of 
all their facidties as well when their bodies 
are immersed in water as when they are on 
dry land. Most savage nations are remark- 
able for this. According to the accounts of 
our late voyagers, the inhabitants of the 
South Sea islands are such expert divers, that 
when a nail or any piece of iron was thrown 
overboard, they would instantly jump into 
the sea after it, and never fail to re- 
cover it, notwithstanding the quick de- 
scent of the metal. Even among civilized 
nations many persons have been found capa- 
ble of continuing an incredible length of 
time under water. The most remarkable in- 
stance of this kind is the famous Sicilian di- 
ver, Nicolo Pesce, who, according to the 
marvellous and indeed incredible account 
given by Kircher, had from his infancy been 
so used to the sea, that at last it became al- 
most his natural element. It is said he was 
frequently known to spend five days in the 
waves without any other provisions than the 
fish which he caught there, and ate raw. He 
often swam over from Sicily into Calabria, a 
tempestuous and dangerous passage, carrying 
letters from the king ; and as frequently swam 
among the gulphsof theLipari islands, no way 
apprehensive of danger. “ In order,” says 
Kircher, “ to aid these powers of enduring 
in the deep, nature seemed to have assisted 
him in a very extraordinary manner: for the 
spaces between his lingers and toes were 
webbed, as in a goose ; and his chest became 
so very capacious, that he could take in, at 
one inspiration, as much breath as would 
serve him for a whole day.” At length, how- 
ever, we are told, this extraordinary person 
met his fate in exploring the depths of Cha- 
rybdis, at the instance of the king ; who, 
after he had once succeeded in bringing up a 
golden cup that had been thrown in/ ordered 
him to repeat the experiment. 
To obviate the inconveniences of diving to 
those who have not the extraordinary powers 
attributed to Nicholas Pesce, different instru- 
ments have been contrived. The chief of 
these is the diving-bell ; which is most con- 
veniently made in form of a truncated cone, 
the smaller base being closed, and the larger 
open. It is to be poised with lead ; and so 
suspended, that the vessel may sink full of 
air, with its open basis downward, and as 
nearly as may be in a situation parallel to 
the horizon, so as to close with the surface of 
the water all at once. The diver sitting un- 
der this, sinks down with the included air to 
the depth desired ; and if the cavity of the 
vessel can contain a tun of water, a single 
man may remain a full hour, without much 
inconvenience, at five or six fathoms deep. 
But the lower lie goes, the included air con- 
tracts itself according to the weight of the 
water which compresses it ; so that at thirty- 
three feet deep the bell becomes half full of 
water, the pressure of the incumbent water 
being then equal to that of the atmosphere ; 
and at all other depths the space occupied by 
the compressed air in the upper part of the 
bell will be to the under part of its capacity 
filled with water, as thirty-three feet, to the 
surface of the water in the bell below the 
common surface. And this condensed air 
being taken in with the breathsoon accommo- 
dates itself to the existing circumstances so 
as to lwve no ill effect, provided the bell is 
permitted to descend slowly. But the greatest 
inconvenience of this engine is, that the wa- 
ter entering it contracts the bulk of air into 
so small a compass, that it soon heats, and 
becomes unlit for respiration : so that there 
is a necessity for its being drawn up to re- 
cruit it ; besides the uncomfortable situation 
of the diver, who must be almost covered 
with water. 
To obviate these difficulties of the diving- 
bell, Dr. Halley, to whom we owe the pre- 
ceding account, contrived a farther appara- 
tus, whereby not only to recruit the air from 
time to time, but also to keep the water 
wholly out of the machine at any depth. 
This bell was made of wood, containing 
about sixty cubic feet in its concavity ; and 
was of the form of a truncated cone, whose 
diameter at the top was three feet, and at the 
bottom five. It was so loaded with lead, that 
3 Y 2 
539 
it would go down in a perpendicular direc- 
tion, and no other. In the top was a win- 
dow to let in light, and likewise a cock to let 
out the hot air that had been breathed; and 
below, about a yard under the bell, was a. 
stage, suspended by three ropes, each of 
which was charged with about one hundred- 
weight to keep it steady. r Fo supply air 
the bell had a couple of barrels, so cased 
with lead as to sink when empty ; each hav- 
ing a bunghole in its lowest part 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. To a hole 
in the uppermost part of these was fixed a 
leathern trunk or hose, long enough to fall 
below the bunghole, and kept down by a 
weight in such a way that the air in the 
upper part of the barrels could not escape, 
unless the lower ends of these hose were first 
lifted up, These air-barrels w r ere made to 
rise and fall like two buckets in a well. By 
means of these barrels fresh air was conti- 
nually supplied from above ; and it was done 
with so much ease, that two men, with less 
than half their strength, could perform all the 
labour required. By an additional contriv- 
ance it was found practicable for a diver to 
go out of the engine to some distance from 
it, the air being conveyed to him in a conti 1 
nued stream by small flexible pipes. Some 
idea of Dr. Halley’s machine may he formed 
from the inspection of Plate Miscel. fig. 50 
where the divers are seen at work. B, L, K, R, 
I, M, P, represent the body of the bell. B, 
the glass which serves as a window. II, the 
cock for letting out the air which has been 
breathed. L, M, the seats. C, one of the 
air-barrels. P, Q, two of the divers. F, 
another diver at a distance from the bell, and 
breathing through the flexible tube K. This 
diver is supposed to have a head-piece of 
lead, made to sit quite close about his 
shoulders: this head-piece is capable of con- 
taining as much air as will supply him for a 
minute or two. When he had occasion for 
more air he turned a cock at F, by which 
means a communication was opened with the 
air in the bell, and thus he could receive a 
new supply at pleasure. 
Since the invention of the diving-bell there 
has been one contrived by Mr. Triewald, 
military architect to the king of Sweden, 
which, for a single person, is in some re- 
spects thought to be more eligible than Dr. 
Halley’s, and is constructed as follows; AB, 
Plate Miscel. iig. 51, is the bell, which is 
sunk by leaden weights D D, hung to its 
bottom. This bell is of copper, and tinned 
all over on the inside, which is illuminated 
by strong convex lenses, G, G, G, with cop- 
per lids H, II, H, to defend them. The 
iron ring or plate, E, serves the diver to 
stand on when he is at work ; and is suspend 
ed at such a distance from the bottom of the 
bell by the chains F, F, F, that when the 
diver stands upright his head is just above 
the water in the bell, where the air is much 
better than higher up, because it is colder, 
and consequently more fit for respiration. 
But as the diver must always be within the 
bell, and his head of course in the upper 
part, the inventor has contrived that, even 
there, when he has breathed the hot air as 
well as he can, he may, by means of a spiral 
copper tube b C, placed close to the inside 
of the bell, draw the cooler and fresher air 
