154 FARADAY 



you taw in the case of the bladder, and which you shall 

 better here. I have tied over this jar a piece of sheet India 

 rubber, and I am now about to take away the air from the 

 inside of the jar; and if you will watch the India-rubber 

 which acts as a partition between the air below and the air 

 above you will see, when I pump, how the pressure shows 

 itself. See where it is going to : I can actually put my hand 

 into the jar; and yet this result is only caused by the great 

 and powerful action of the air above. How beautifully it 

 shows this curious circumstance I 



Here is something that you can have a pull at when I 

 have finished to-day. It is a little apparatus of two hollow 

 brass hemispheres, closely fitted together, and having con- 

 nected with it a pipe and a cock, through which we can 

 exhaust the air from the inside; and although the two 

 halves are so easily taken apart while the air is left within, 

 yet you will see, when we exhaust it by-and-by, no power 

 of any two of you will be able to pull them apart. Every 

 square inch of surface that is contained in the area of that 

 vessel sustains fifteen pounds by weight, or nearly so, when 

 the air is taken out, and you may try your strength presently 

 in seeing whether you can overcome that pressure of the 

 atmosphere. 



Here is another very pretty thing the boys* sucker, only 

 refined by the philosopher. We young ones have a perfect 

 right to take toys, and make them into philosophy, inasmuch 

 as nowadays we are turning philosophy into toys. Here is 

 a sucker, only it is made of India-rubber. If I clap it upon 

 the table, you see at once it holds. Why does it hold? I 

 can slip it about, and yet if I try to pull it up, it seems as 

 if it would pull the table with it. I can easily make it slip 

 about from place to place, but only when I bring it to the 

 edge of the table can I get it off. It is only kept down by 

 the pressure of the atmosphere above ; we have a couple of 

 them, and if you take these two and press them together, 

 you will see how firmly they stick. And, indeed, we may 

 use them as they are proposed to be used, to stick against 

 windows or against walls, where they will adhere for an 

 evening, and serve to hang any thing on that you want. I 

 think, however, that you boys ought to be shown experi 



