BOOK XI 



ELECTRICITY. 



GENERAL REMARKS. 



fpLECTRICITY in the form in which it was originally studied 

 --^ Franklinic, frictional, or statical electricity has been so com- 

 pletely identified with electricity in its more comprehensive form 

 Voltaic, chemical, or dynamical electricity that any additions we 

 might have to make to the history of the earlier form of the subject 

 Ure included in the later science. 



There are, however, several subjects which may still be regarded 

 rather as branches of Electricity than of the Cognate Sciences. Such 

 are, for instance, Atmospheric Electricity, with all that belongs to 

 Thunderstorms and Lightning Conductors. The observation of 

 Atmospheric Electricity has been prosecuted with great zeal at 

 various meteorological observatories ; and especially at the Observa- 

 tory established by the British Association at Kew. The Aurora 

 Borealis, again, is plainly an electrical phenomenon ; but probably 

 belonging rather to dynamical than to statical electricity. For it 

 strongly affects the magnetic needle, and its position has reference to 

 the direction of magnetism ; but it has not been observed to affect the 

 electroscope. The general features of this phenomenon have been 

 described by M. de Humboldt, and more recently by M. de Bravais ; 

 and theories of the mode of its production have been propounded by 

 MM. Biot, De la Rive, Kaemtz, and others. 



Again, there are several fishes which have the power of giving an 

 electrical shock : the torpedo, the gymnotus, and the silurus. The 

 agency of these creatures has been identified with electricity in the 

 most general sense. The peculiar energy of the animal has been made 

 to produce the effects which are produced by an electrical discharge 

 or a voltaic current : not only to destroy life in small animals, but to 



