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FARADAY 



bottle again to the balance, and if it is now counterpoised 

 by the original weight, we shall be quite sure we have made 

 our experiment correctly It is bal- 

 anced, so, you see v we can find out 

 the weight of the extra volumes of 

 air forced in in that way, and by 

 that means we are able to ascertain 

 that a cubic foot of air weighs I 1-5 

 oz But that small experiment will 

 by no means convey to your mind 

 the whole literal truth of this mat- 

 ter It is wonderful how it accumu- 

 lates when you come to larger vol- 

 umes This bulk of air [a cubic foot] 

 weighs 11-5 oz What do you think 

 of the contents of that box above 

 there which I have had made for the 

 purpose? The air which is within 

 that box weighs one pound a full 

 pound 5 and I have calculated the 

 weight of the air in this room:; you 

 would hardly imagine it, but it is above a ton. So rapidly 

 do the weights rise up, and so important is the presence of 

 the atmosphere, and of the oxygen and the nitrogen in 

 it, and the use it performs in conveying things to and fro 

 from place to place, and carrying bad vapors to places where 

 they will do good instead of harm. 



Having given you that little illustration with respect to 

 the weight of the air, let me show you certain consequences 

 of it You have a right to them, because you would not 

 understand so much without it Do you remember this kind 

 of experiment? have you ever seen it? Suppose I take a 

 pump somewhat similar to the one I had a little while ago 

 to force air into the bottle, and suppose I place it in such 

 a manner that by certain arrangements I can apply my 

 hand to it My hand moves about in the air so easily that 

 it seems to feel nothing, and I can hardly get velocity 

 enough by any motion of my own in the atmosphere to 

 make sure that there is much resistance to it But when I 

 put my hand here [on the air-pump receiver, which was 



FIG. 80 



