LESSORS IN ELECTRICITY. 607 



ized truths they are. The " Principles of Biology " is thus an attempt 

 to explain the phenomena called vital, by general -laws common to 

 phenomena of every kind. 



\To be continued.] 



-- 



LESSONS IN ELECTRICITY.' 



HOLIDAY LECTURES AT THE ROYAL INSTITUTION. 

 Br Peofessob TYNDALL, F.K.S. 



I. 

 QIECTIOX 1. Introduction. Many centuries before Christ, it had 

 O been observed that yellow amber {elektron) when rubbed pos- 

 sessed the power of attracting light bodies. Thales, the founder of 

 the Ionic philosophy (b. c. 580), imagined the amber to be endowed 

 with a kind of life. 



This is the germ out of which has grown tlie science of electricity^ 

 which takes its name from the substance in which this power of at- 

 ti'action was first observed. 



It will be my aim, during six hours of these Christmas holidays, 

 to make you, to some extent, acquainted with the history, 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 science, 

 which is called " Frictional Electricity," because in it the electrical 

 power is obtained from the rubbing of bodies together. 



Sec. 2. Historic Notes. The attraction of light bodies by rubbed 

 amber was the sum of the world's knowledge of electricity for more 

 than 2,000 years. In 1600 Dr. Gilbert, physician to Queen Elizabeth, 

 whose attention had been previously directed with great success to 

 magnetism, vastly expanded the domain of electricity. lie showed 

 that not only amber, but various spars, gems, fossils, stones, glasses, 

 and resins, exhibited when rubbed the same power as ambei'. 



Robert Boyle (1675) proved that a suspended piece of rubbed 

 amber, which attracted other bodies to itself, was in turn attracted 

 by a body brought near it. He also observed the light of electricity, 

 a diamond, with which lie experimented, being found to emit light 

 when rubbed in the dark. 



Boyle iniagined that the electrified body threw out an invisible, 

 glutinous substance, which laid hold of light bodies, and, returning to 

 the source from which it emanated, carried them along with it. 



' A course of six lectures, with simple experiments in frictional electricity, before 



juvenile audiences during the Christmas holidays. 



