DIVING BELL. 
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, eacli of which was charged with 
about one hundred w'eiglit to keep it stea- 
dy. To supply air, the bell had a couple of 
barrels so- cased with lead as to sink when 
empty, each having a bung-hole in its lowest 
part to let in the water as the air in tliem 
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 bpng-hole, 
and kept down by a weight in such a way 
that the air in the upper part of the barrels 
could not escape, tinless the lower ends of 
these hose were first lifted up. These air 
barrels were made to rise and fall like two 
buckets in a well, by means of these barrels 
fresh air was continually 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 re- 
quired. 15y an additional contrivance 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 con- 
tinuable stream by small flexible pipes. 
A great improvement in the diving bell 
was made by the late Mr. Spalding, of Edin- 
burgh. This construction seems designed 
to remedy some inconveniences of Dr. 
Halley, which are very evident, and of a 
very dangerous tendency ; these are, 1. by 
Dr. Halley’s constructions, the sinking or 
rising of the bell depends on the people who 
are at the surface of the water, as the bell 
when in the water has a very considerable 
weight, the raising it. not only requires a 
great deal of labour, but there is a possibi- 
lity of the rope breaking, by which it is rais- 
ed, and thus every person in the bell would 
inevitably perish : 2. As there are in many 
parts of the sea rocks which lay .at a consi- 
derable depth, the figure of which cannot 
possibly be perceived from above, tliere is 
danger that some of their ragged promi- 
nences, may catch hold of one of the edges 
of the bell in its descent, and thus overset 
it before any signal can be given to those 
above, which would infallibly be attended 
with the destruction of the people in the 
bell ; and as it must always be unknown 
before trial what kind of a bottom the sea 
has in any place, it is plain, that without 
some contrivance to obviate this last danger, 
the descent in Dr. Halley’s diving bell is not 
at all eligible. 
How these inconveniencies are remedied 
by Mr. Spalding’s new contrivance, will be 
easily understood from the following des- 
criptions, A B C D fig. 3, represents a sec- 
tion of the bell which is made of wood, e e are 
iron hooks, by means of which it is suspended 
by ropes Q B F c and Q A E « and Q S as 
expressed in the figure c c are iron hooks, to 
which are appended leaden weights, that 
keep the mouth of the bell always parallel to 
the surface of the water, whether the ma- 
chine taken altogether is lighter or heavier 
than an equal bulk of water. By these 
weights alone, howSver, the bell would not 
sink, another is therefore added, represented 
at L, and vvhich can be raised or lowered 
at pleasure, by means of a rope passing 
over the pulley a, and fastened to the sides 
of tlie bell M. As the bell descends, tills 
weight, cjilled by Mr. Spalding the balance 
weight, hangs down a considerable way be- 
low tile mouth of the bell. In case the edge 
ot the bell is caught by any obstacle, the 
balance weight is immediately lowered 
down, so that it may rest upon the-bottom, 
by this means the bell is lightened, so that 
all danger of oversetting is removed, for 
being lighter without the balance weight 
than an equal bulk of water, it is evident 
tliat the bell will rise as far as the length of 
the rope affixed to the balance weight will 
allow it. This weight therefore will serve 
as a kind of anchor to keep the bell at any 
particular depth which the divers may tliink 
necessary, or by pulling it quite up, the 
descent may be continued to the very bot- 
tom. 
By another very ingenious contrivance, 
Mr. Spalding rendered it possible for the 
divers to raise the bell with all the weights 
appended to it, even to the surface, or to 
stop at any particular depth as they think 
proper ; and thus they could still be safe, 
even though the rope designed for pulling 
up the bell w'as broken ; for this purpose, the 
bell is divided into two cavities, both of 
which are made as tight as possible ; just 
above the second bottom, EF, are small slits 
on the sides of the bell through which the 
water entering as the bell descends, dis- 
places the air originally contained in its ca- 
vity, which flies out at the upper orifice of 
the cock H. When this is done, the divers 
turn the handle which stops the cock, so 
that if any more air was to get into the ca- 
vity AEFB, it could no longer be dis- 
charged through the orifice H as before. 
When this cavity is full of water, the bell 
sinks, but when a considerable quantity of 
