CHEMICAL HISTORY OF A CANDLE 155 



ments that you can make at home; and so here is a very 

 pretty experiment in illustration of the pressure of the 

 atmosphere. Here is a tumbler of water. Suppose I were 

 to ask you to turn that tumbler upside down so that the 

 water should not fall out, and yet not be kept in by your 

 hand, but merely by using the pressure of the atmosphere; 

 could you do that? Take a wine-glass, either quite full or 

 half full of water, and put a flat card on the top; turn it 

 upside down, and then see what becomes of the card and 

 of the water. The air can not get in because the water, by 

 its capillary attraction round the edge, keeps it out. 



I think this will give you a correct notion of what you 

 may call the materiality of the air; and when I tell you that 

 that box holds a pound of it, and this room more than a ton, 

 you will begin to think that air is something very serious. 

 I will make another experiment to convince you of this 

 positive resistance. There is that beautiful experiment of 

 the popgun, made so well and so easily, you know, out of a 

 quill, or a tube, or any thing of that kind; where we take 

 a slice of potato, for instance, or an apple, and take 

 the tube and cut out a pellet, as I have now done, and push 

 it to one end. I have made that end tight; and now I take 

 another piece and put it in: it will confine the air that is 

 within the tube perfectly and completely for our purpose; 

 and I shall now find it absolutely impossible by any force 

 of mine to drive that little pellet close up to the other. It 

 can not be done; I may press the air to a certain extent, 

 but if I go on pressing, long before it comes to the second 

 the confined air will drive the front one out with a force 

 something like that of gunpowder ; for gunpowder is in part 

 dependent upon the same action that you see here exem- 

 plified. 



I saw the other day an experiment which pleased md 

 much, as I thought it would serve our purpose here. (1 

 ought to have held my tongue for four or five minutei 

 before beginning this experiment, because it depends upon 

 my lungs for success.) By the proper application of air, I 

 expect to be able to drive this egg out of one cup into the 

 other by the force of my breath ; but if I fail it is in a good 

 cause, and I do not promise success, because I have been 



