GRAVITATION IN TACUO. 29 



remove the air by means of an air pump, and 

 while that is being done, let me show you 

 another experiment of the same kind. Take 

 a penny-piece, or a half-crown, and a round 

 piece of paper a trifle smaller in diameter than 

 the coin, and try them side by side to see 

 whether they fall at the same time [dropping 

 them]. You see they do not the penny- 

 piece goes down first. But, now place this 

 paper flat on the top of the coin, so that it shall 

 not meet with any resistance from the air, and 

 upon then dropping them you see they do both 

 fall in the same time [exhibiting the effect]. I 

 dare say if I were to put this piece of gold leaf, 

 instead of the paper, on the coin, it would do 

 as well. It is very difficult to lay the gold leaf 

 so flat that the air shall not get under it and 

 lift it up in falling, and I am rather doubtful 

 as to the success of this, because the gold leaf 

 is puckery ; but will risk the experiment. There 

 they go together! [letting them fall] and you 

 see at once that they both reach the table at 

 the same moment. 



We have now pumped the air out of the ves- 

 sel, and you will perceive that the gold leaf 

 will fall as quickly in this vacuum as the coin 



