202 Mr. W. Sturgeon on the Theory of Magnetic Electricity. 



Position 2. — The excitation depends upon a disturbance 

 of the equilibrium of the electric fluid natural to the metal ; 

 by its impinging on the exciting polar magnetic lines) and 

 is accomplished by mechanical motion, either of the metallic 

 body to be excited, or of the magnet, — or of both at the 

 same time. For simplification, however, we will suppose the 

 magnet to be stationary, and the metallic body alone to be put 

 into motion. 



Remark. — As the electric fluid by this process has not as 

 yet been recognised in any other state than that of motion, 

 the phaenomena are necessarily displayed upon the principles 

 of electro-dynamics. Hence the term " excitation" in this place 

 is to be considered not only expressive of a process for sim- 

 ply disturbing the electric fluid, but as one which is capable 

 of communicating to various quantities of it an infinite variety 

 of velocities. And as the quantity of fluid in motion, and the 

 velocity with which it moves, will, conjointly, constitute an 

 electro-momentum, which at all times will be proportional to 

 the product of its constituent elements; it is therefore the 

 production of the, electro-momentum which is to be understood, 

 when we speak of various degrees of excitation. 



Indeed, whatever may be the nature of the exciting agent, 

 or the mode of its application, it is in this sense only that the 

 term excitation can, with any degree of propriety, be applied 

 when electric currents and tneir effects are the phaenomena 

 under contemplation. Electro-momentum is an expression 

 which at once conveys to the mind the author's meaning, — 

 that it is the production of the velocity multiplied into the 

 quantity of electric matter which, by the process, whatever 

 may be its character, is impelled into motion from its previous 

 statical repose. 



Electric currents generated by a voltaic battery are consti- 

 tuted of distinct alternate charges and discharges of the electric 

 matter, or of electro-pulsations ; and may be assimilated to 

 the currents of blood through the animal system, which are 

 produced by the alternate charges and discharges at the heart. 

 And it is very far from being improbable that both are actu- 

 ated upon the same principle. The electric fluid called forth 

 by a voltaic battery is, therefore, alternately accumulating and 

 discharging during the whole time the instrument is in ac- 

 tion. In the former case the intensity is exalting; but it is in 

 the latter alone that the force is exhibited ; which force is the 

 production of the quantity of fluid discharged, and the velocity 

 with which it moves conjointly; which may very clearly be 

 understood by the term electro-momentum. 



A*, however, the electro-pulsations in most cases are pro- 



