Compressed Air Work And Diving 1909

32 COAIPRESSED AIR WORK. closing it. Fortunately this valve was not so important as the other one. I here were, it will be remembered, two valves and a cloor to shiit, and it was Lambert’s shiitting of the other valve and the cloor which enablecl the water to be got under. If a glass tumbler be submergecl face downwards in a basin of water, the water will be prevented from rising by the pressure of air inside the tumbler, about 14.7 Ibs. per squai e inch, which is the same as that of the atmos- phci e pressing 011 the exposecl surface of the water in the basin. As the tumbler is still presseel downwards the water gradually rises, and as it cloes- so compresses the air inside, because the pressure of the air on the exposecl surface of water is helpecl by the head of water from the lip of the tumbler to the surface of the water in the basin, and if the tumbler were submergecl to a depth of 33 ft. in salt water, and was in shape truly cylinclrical, the water woLikl rise half way up it. This is the principle of the earlier diving belis, and they were no doubt made beil shaped in order that the maximum compression might be obtained with a mini- mum rise of water level in the beil itself. The idea of using compressed air to keep clown the water originated with Edm. Halley, Secretary to the Royal Society, about the year 1714,* and he aclopted the following ingenious methoel for compressing the air. Casks were provided with a bung hole in the bottom and another hole in the top fitteel with a llexible pipe. l'his pipe was open at the end, but had a weight fixed to it, so that when in the water this end was below the bottom bung hole. As the cask was lowerecl into the water, the water was aclmittecl through the bung hole and compressed the air inside the * Proc. Royal Society, vol. xix.