It is evident, therefore, that if an enlarged tumbler could be lowered to the bed of the sea, a man might be enclosed within it, and for a time be able to support life by means of the air contained within the “bell,” as this enlarged tumbler was popularly called.
It is equally evident that within a short time the air within the bell must be exhausted, and that, unless a fresh supply could be introduced, the diver within the bell would be as effectively drowned as if there were no bell at all.
The accompanying illustration is a kind of chart, so to speak, of the mode in which air was formerly supplied to the bell.
On the right hand is seen a section of the Diving-bell itself, together with the seat on which the divers can rest. There is also an escape-valve at the top of the bell, by which the vitiated air can pass away; but, as it is not essential to the subject in hand, and is rather complicated in structure, it has been omitted.
Immediately on the left of the bell is a cask, to which several heavy weights are attached. This cask contained compressed air, and, after it was lowered by the side of the bell, the end of the flexible tube was taken into the bell, the tap turned, and the compressed air rushed into the bell, taking the place of that which had been exhausted by respiration, and was allowed to pass through the escape-valve. I may mention that the divers unexpectedly discovered that, when they were breathing compressed air, they could dispense with respiration for a wonderfully long time, the amount of oxygen taken in at a single breath being enough to renovate the blood more than could be done by several ordinary inspirations.
On the left hand of the illustration is seen a sketch of the nest of the now familiar Water-spider (Argyronetra aquatica), taken from some specimens in my possession.
The Water-spider is really a remarkable being. Itself a denizen of air, breathing our earthly atmosphere just as we do, and as capable of being drowned as ourselves, it nevertheless passes nearly the whole of its existence under water, and in that strange locality lays its eggs and rears its young. How this wonderful feat is performed we shall now see.
When the female Water-spider wishes to deposit her eggs, she looks out for a suitable locality, and, being a good diver, tests the various aquatic herbage until she has found a favourable spot, and then sets to work on her remarkable nest, which I believe is quite original in zoology.
After stretching a few stout threads by way of a scaffolding, she attaches to the plant a small silken cell, shaped very much like an acorn, but not so large. Ascending to the surface of the water, she contrives to clasp a bubble of air between her last pair of legs, and, laden with this airy treasure, dives below.