_A._ As broad as you will, so it be broad enough to pour into it quicksilver. And fill it with quicksilver, and stop up the entrance with your finger, so as to unstop it again at your pleasure. Then set down a basin, or, if you will, a sea of quicksilver, and inverting the cylinder full as it is, dip the end into the quicksilver, and remove your finger, that the cylinder may empt itself. Do you conceive me? For there is so many passing by, that I cannot paint it. _B._ Yes, I conceive you well enough. What follows? _A._ The quicksilver will descend in the cylinder, not till it be level with that in the basin, according to the nature of heavy fluids, but stay and stand above it, at the height of twenty-nine inches or very near it, the bottom being now uppermost, that no air can get in. _B._ What do you infer from this? _A._ That all the cavity above twenty-nine inches is filled with vacuum. _B._ It is very strange that I, from this same experiment, should infer, and I think evidently, that it is filled with air. I pray, tell me, when you had inverted the cylinder, full as it was, and stopped with your finger, dipped into the basin, if you had then removed your finger, whether you think the quicksilver would not all have fallen out? _A._ No sure. The air would have been pressed upward through the quicksilver itself: for a man with his hand can easily thrust a bladder of air to the bottom of a basin of quicksilver. _B._ It is therefore manifest that quicksilver can press the air through the same quicksilver. _A._ It is manifest; and also itself rise into the air. _B._ What cause then can there be, why it should stand still at twenty nine inches above the level of the basin, rather than any place else? _A._ It is not hard to assign the cause of that. For so much quicksilver as was above the twenty-nine inches, will rise the first level of that in the basin, as much as if you had poured it on; and thereby bring it to an equilibrium. So that I see plainly now, that there is no necessity of vacuum from this experiment. For I considered only that naturally quicksilver cannot ascend in air, nor air descend in quicksilver, though by force it may. _B._ Nor do I think that Torricellius or any other vacuist thought of it more than you. But what is the second experiment?