ELECTRICAL ATTRACTION. 113 



which we may not use. Here are some indica- 

 tors (fig. 36). I bend round a strip of paper into 



Fig. 36. 



a hoop, and we have as good an indicator as can 

 be required ; see how it rolls along, travelling 

 after the sealing-wax. If I make them smaller, 

 of course we have them running faster, and 

 sometimes they are actually attracted up into 

 the air. Here also is a little collodion balloon. 

 It is so electrical that it will scarcely leave my 

 hand unless to go to the other. See, how 

 curiously electrical it is ; it is hardly possible 

 for me to touch it without making it electrical ; 

 and here is a piece which clings to anything it 

 is brought near, and which it is not easy to lay 

 down. And here is another substance, gutta- 

 percha, in thin strips ; it is astonishing how by 

 rubbing this in your hands you make it electri- 

 cal ; but our time forbids us to go further into 

 I 



