130 



MAGNETS AND ELECTRICITY 



6. How could ships be steered in the right direction, out of sight of 

 land, without the use of a compass? 



7. Why are some magnets made in horseshoe form? 



141. Electric Charges from Friction. If a glass rod is 

 rubbed with silk, the rod will attract light bodies, such 

 as paper, pith balls, cork, etc. (Fig. 117). If 

 a pane of glass is placed upon two books, 

 and rubbed with silk (Fig. 118), bits of paper 

 or cork that are placed under the glass will 

 be set in motion. A stick of sealing wax, or 

 a hard-rubber ruler or comb, has the same 

 power after it has been rubbed with fur or 

 flannel or hair. The silk, flannel, and hair 

 become electrified, as well 

 as the glass, wax, and rub- 

 ber. In fact, any two 

 unlike substances are FIG. us. 



j e n * th move up and 



Fia. 117. 

 The charged 

 rod first at- 

 tract s and 

 then repels 

 the ball. 



"charged" by rubbing; a part of the 

 muscular energy used up in the rub- 

 bing is changed into electric charges. 



The. ancient Greeks knew that amber, a fossil gum, 

 would attract bodies after being rubbed. Amber was called 

 "electron"; hence our words, electric, electricity, etc. 



142. Conductors and Insulators. Dr. Gilbert, the 

 physician of Queen Elizabeth, thought that some bodies 

 could be electrified by rubbing, and that others could not. 

 So he divided bodies into "electrics" and "non-electrics." 

 Because metal rods, held in his bare hand while being 

 rubbed, were not charged, he called metals "non-electrics." 

 If he had held the metal in a dry wooden or silk handle, 



