Chap. XIII.
1053
comfort . Inside the bell, and immediately over the hole, which admits the air, is screweda piece of stout leather, so that the air only enters through the spaces comprised betweenthe screws; this leather prevents the air, when once admitted, from returning to the hose;and should it burst, the watercannot enter through the air hole;the divers are therefore securedagainst any accident which mightarise from this cause, and the bellcontains a sufficient quantity ofair to support those within it,without the assistance of the air-pump, until it could be raisedup from almost any depth.
When the bell is overchargedwith air, it escapes under its edge,and from its expansive nature,agitates the water as it ascendstowards the surface; this hasbeen supposed to be the foul airescaping, but that which has beenrespired, being lightest, ascendsto the upper part of the bell, anda continued current of air passingfrom the top to the bottom pre-vents any unpleasant effect
There is a movable seat ateach end, and a narrow foot-hoard,with several hooks and shelvesfor the workmen’s tools, and atthe top are two eye-bolts for thepurpose of securing any heavyweights which may be requiredto be raised with the bell.
No difficulty or danger attendsits use, provided the men aresufficiently careful, and the bellis properly suspended : whenimmersed, and the divers requireits position to he changed, theystrike it with a hammer. Eightsignals are made : one strike in-dicates that there is not sufficientair, and that it is necessary towork the pump faster: two an-nuls a former signal: three, that Fig. 1619. plan and section of air-itmp.the bell is to be raised : four to
lower it: five, to move it to the right; six, to the left; seven, backwards and eight, forward :other methods are resorted to for holding a correspondence with those in the vessel, assending up small buoys, &c.
When any work is to be executed by the diving bell, it is important that the watershould be transparent, or at least sufficiently so that objects may be discerned when lyingtwo or three feet below the bell, that the machine may not touch them in its descent: withartificial light it is impossible to distinguish objects in muddy water; but when clear, acloud passing over the sun is perceptible in deep water. The workmen employed usuallyin the summer remain from 7 to 12 o’clock in the morning, and from 1 to 6 o’clock in theevening, and in winter only as long as they can see.
It is necessary to observe that the greatest caution is required in lowering the bell: if itdescend w’ith too great velocity, the air becomes so much compressed as to be injurious tothe lungs of the workmen, sometimes causing immediate death ; when the descent is verygradual, no evil consequences will arise.
The diving bell at Ramsgate liarbour was a square chest of iron, weighing 50 cwt. ; itsdimensions were feet in height and length, and 3 feet in width : it was cast in one piece,and sufficiently heavy to sink itself: by means of a forcing air-pump, worked in a boatmoored immediately over the bell, two men were supplied with fresh air : in the crownwere eight round lenses, 4 inches in diameter, to admit the light. It was at first suspendedfrom shears, but Mr. Gott, the resident engineer, finding them inconvenient, adopted thetraversing crane, which enabled the masons to place the stone in any position required:
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