ELECTRICITY. 



objections would, I considered, be most 

 practically met by showing what could 

 be done, in the way of discipline and in- 

 struction, by experimental lessons involv- 

 ing the use of apparatus so simple and 

 inexpensive as to be within everybody's 

 reach. 



With some amplification, the substance 

 of .our Christmas Lessons is given in the 

 present little volume. 



LESSONS IN ELECTRICITY. 



1. Introduction. 



MANY centuries before Christ, it had 

 been observed that yellow amber (elck- 

 tron\ when rubbed, possessed the power 

 of attracting light bodies. 



Thales, the founder of the Ionic philos- 

 ophy (B.C. 580), imagined the amber to 

 be endowed with a kind of life. 



This is the germ out of which has 

 grown the science of electricity, a name 

 derived from the substance in which this 

 pr.ver of attraction was first observed. 



It will be my aim, during six hours of 

 those Christinas holidays, to make you, 

 to some extent, acquainted with the his- 

 tory, facts, and principles of this science, 

 and to teach you how to work at it. 



The science has two great divisions : 

 the one called " Frictional Electricity," 

 the other "Voltaic Electricity." For 

 the present, our studies will be confined 

 to the first, or older portion of the sci- 

 ence, which is called " Frictional Elec- 

 tricity," because in it the electrical 

 power is obtained from, the rubbing of 

 bodies together. 



2. Historic Note*. 



The attraction of light bodies by 

 rubbed amber was the sum of the world's 

 knowledge of electricity for more than 

 2000 years. In 1600 Dr. Gilbert, phy- 

 sician to Queen Elizabeth, whose atten- 

 tion had been previously directed with 

 great success to magnetism, vastly ex- 

 panded the domain of electricity. He 

 showed that not only amber, but various 

 spars, gems, fossils, stones, glasses, and 

 rosins, exhibited, when rubbed, the same 

 power as amber. 



Robert Boyle (1675) proved that a 

 suspended piece of rubbed amber, which 



attracted other bolie.* to itself, was in 

 turn attracted by a body brought near it. 

 He also observed the light of electricity, 

 a diamond, with which he experimented, 

 being found to emit light when rubbe I 

 in the dark. 



Boyle imagined that the electrified 

 body threw out an invisible, glutinous 

 substance, which laid hold of light bodie*, 

 and, returning to the source from which 

 it emanated, carried them along with it. 



Otto von Guericke, Burgomaster of 

 Magleburg, contemporary of Boyle, and 

 inventor of the air-pump, intensified the 

 electric power previously obtained. He 

 devised what may be called the first elec- 

 trical machine, which was a ball of 

 sulphur, about the size of a child's head. 

 Turned by a handle, and rubbed by the 

 dry hand, the sulphur sphere emitted 

 light in the dark. 



Von Guericke also noticed, and this is 

 important, that a feather, having been 

 first attracted to his sulphur globe, was 

 afterward repelled, and kept at a dis- 

 tance from it, until, having touched 

 another body, it was again attracted. 

 He heard the hissing of the " electric 

 lire," and also observed that an unelec- 

 trified body, when brought near his ex- 

 cited sphere, became electrical and capa- 

 ble of being attracted. 



The members of the Academy del 

 Cimento examined various substances 

 electrically. They proved smoke to be 

 attracted, but not flame, which, they 

 found, deprived an electrified body of its 

 power. 



They also proved liquids to be sensible 

 to the electric attraction, showing that 

 when rubbed amber was held over the 

 surface of a liquid, a little eminence was 

 formed, from which the liquid was finally 

 discharged against the amber. 



Sir Isaac Newton, by rubbing a flat 

 glass, caused light bodies to jump be- 

 tween it and a table. He also noticed 

 the influence of the rubber in electric ex- 

 citation. His gown, for example, was 

 found to be much more effective than a 

 napkin. 



Newton imagined that the excited body 

 emitted an elastic fluid which penetrated 

 glass. 



In the ^ efforts of Thales, Boyle, and 

 Newton to form a mental picture of elec- 

 tricity we have an illustration of the ten- 



