You can press air, the same as you can press wood, or paper, or cloth, so that it will go into a smaller space than it occupied before you pressed it. Did you ever make a pop-gun? "Oh, yes, sir, a hundred times." Well, when you send the wad out of the pop-gun, you do it by pressing the air inside the tube. Now if your tumbler was a hundred or a thousand times as large, the air would prevent the water from coming in, just as it does in this instance. Suppose I had dropped a purse full of gold into a very deep river, and it had sunk to the bottom. Suppose I could not get it in any other way but by going down to the bottom after it. I could go down to that depth, and live there for some time, by means of a diving bell made large enough to hold me, precisely in the same way that a bird might go down to the bottom of a tub of water, in a tumbler, and stand there with the water hardly over his feet. There is a good deal of machinery about a diving bell, it is true. But I need not take up much time in describing it. It is necessary for the man to breathe, of course, while he is in the diving bell; and as the air it contains is soon rendered impure by breathing, fresh air must be introduced into the bell by means of a pump, or in some other way. I am not very familiar with the necessary machinery, to tell the truth. I never explored the bottom of a river in this way, and I think it will be a long time before I make such a voyage. The diving bell has been used for a good many useful purposes--to lay the foundations of docks and the piers of bridges; to collect pearls at Ceylon, and coral at other places. I am not sure but the diving bell is getting somewhat out of use now. People have found out another way of groping along on the bottom of rivers and seas. They do it frequently, I believe, by means of a kind of armor made of India rubber. But so far as my book is concerned, it is of no consequence whether the diving bell is out of use or not. I shall use the title, at all events. If, after my account of the diving bell, you still ask why I choose to give such a name to the budget I have prepared for you, I can answer your question very easily.