IN the earlier stages of the diver’s art the Diving-bell afforded the only means of gaining access to the bed of the sea, even in comparatively shallow waters. The mode in which this result was obtained was simple enough, and though it carried with it the germs of still greater improvements, was but limited and uncertain in its action. The reader is probably aware that if a vessel be filled with air, no liquid can obtain admittance until a corresponding amount of air be set free. Suppose, for example, that an empty tumbler be inserted over a basin of very clean water, and pressed downwards, it will be found that scarcely any water will enter it, the air having taken up all the available space, and only allowing as much space as may be accounted for by its faculty of compression. 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. [Illustration: NEST OF WATER-SPIDERS.] [Illustration: DIVING-BELL.] 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.