

ELECTRICAL APPARATUS. 



ELECTRICAL phenomena are usually and conveniently divided 

 into two chief classes ; the first comprising those which depend 

 upon the mutual action of bodies while they are in different 

 electrical conditions, and the second including those which 

 accompany the process of electrical equalization. Phenomena of 

 the former class, since they depend on the existence of a particular 

 electrical state in the bodies which produce them, are appropriately 

 called ELECTRO-STATICAL; while those of the latter class, which 

 depend upon the occurrence of an electrical process, requiring the 

 -expenditure of energy in some shape or other in order that it 

 may go on continuously, are called ELECTRO -DYNAMICAL. 



I. ELECTRO-STATICS. 



The first condition for the production of any electro-statical 

 phenomenon is that we should have the means of developing the 

 electrical condition.* Instruments for this purpose are com- 

 monly called electrical machines. 



* Or rather conditions, for, as is well-known, there are two antagonistic 

 electrical states, so related that a body is never electrified in one way without 

 another body being electrified in the opposite way and to the same extent. It 

 often happens, however, that when a body such as can be employed in our experi- 

 ments is electrified in one way, the body to which the correlative equal and 

 opposite electrification is imparted is the earth, whose size is so great that its 

 electrical state is not sensibly affected by any amount of electrification that can 

 be produced artificially : in such cases the apparent result is the development 

 of one kind of electrification only. 



