CHAPTER X. 



FRICTION AL ELECTRICITY AND MAGNETISM. 



IF a dry glass tube, as a lamp chimney, is rubbed vigorously 

 with a piece of dry flannel for a moment or so, it will attract 

 small pieces of paper or pith, which, after remaining a short 

 time in contact, are repelled. After being rubbed, if the glass 

 tube is held near the cheek, a gentle breeze will seem to blow 

 against the cheek, and perhaps a pricking sensation may be felt 

 and crackling sounds be heard. Like phenomena sometimes occur 

 when stroking a cat or while combing the hair with a hard-rub- 

 ber comb. Sealing wax when rubbed in the same way exhibits 

 the same property. Bodies having this property are said to be 

 electrified. 



When a glass tube is rubbed with a piece of flannel, only 

 the part rubbed will be electrified, and the same is true of sealing 

 wax. In these bodies electricity does not pass from one part to 

 another; that is, they do not conduct electricity, but when met- 

 als become electrified by friction or otherwise in any of their 

 parts the electricity immediately spreads out over the en- 

 tire surface, that is, metals do conduct electricity. Bodies 

 which resist the spread or passage of electricity through them 

 are called poor conductors, or non-conductors; while others 

 which resist the passage of electricity but slightly are called 

 good conductors. The difference between these two classes of 

 bodies is in the quantity of electricity they convey, as no body 

 is absolutely a non-conductor. Nearly all the metals are good 

 conductors of electricity, and so are graphite, water, charcoal, 

 animal and vegetable bodies and other substances, while lime, 

 India rubber, silk, diamond, wax, resin, air and other bodies are 

 poor conductors. A good conductor retains electricity only so 



(87) 



