FARADAY 



this by an experiment which, if you are very clever, some 

 of you may even have skill enough to repeat. Here is our 



generator of hy- 

 drogen, and here 



'( 



v-v, ( _-_i_v. ... _^- are some soap- 



suds. I have an 



India-rubber tube connected with the hydrogen gen- 

 erator, and at the end of the tube is a tobacco-pipe. I 

 can thus put the pipe into the suds and blow bubbles 

 by means of the hydrogen. You observe how the 

 bubbles fall downward when I blow them with my 

 warm breath; but notice the difference when I blow 

 them with hydrogen. [The lecturer here blew bubbles 

 FIG. 72 with hydrogen, which rose to the roof of the theatre.] 

 It shows you how light this gas must be in order to carry 

 with it not merely the ordinary soap-bubble, but the larger 

 portion of a drop hanging to the bottom of it. I can show its 

 lightness in a better way than this ; larger bubbles than these 

 may be so lifted up; indeed, in former times balloons used to 

 be filled with this gas. Mr. Anderson will fasten this tube on 

 to our generator, and we shall have a stream of hydrogen 

 here with which we can charge this balloon made of col- 

 lodion. I need not even be very careful to get all the air out, 

 for I know the power of this gas to carry it up. [Two collo- 

 dion balloons were inflated and sent up, one being held by a 

 string.] Here is another larger one, made of thin mem- 

 brane, which we will fill and allow to ascend; you will see 

 they will all remain floating about until the gas escapes. 



What, then, are the comparative weights of these sub- 

 stances ? I have a table here which will show you the propor- 

 tion which their weights bear to each other. I have taken 

 a pint and a cubic foot as the measures, and have placed 

 opposite to them the respective figures. A pint measure 

 of this hydrogen weighs three quarters of our smallest 

 weight, a grain, and a cubic foot weighs one twelfth of 

 an ounce; whereas a pint of water weighs 8750 grains, 

 and a cubic foot of water weighs almost 1000 ounces. 

 You see, therefore, what a vast difference there is be- 

 tween the weight of a cubic foot of water and a cubic 

 foot of hydrogen* 



