J. C. Maxwell’s, ‘Dynamical theory of the electromagnetic field’

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                                (9) We may now consider another phenomenon observed in 
the electromagnetic field. When a body is moved across 
the lines of magnetic force it experiences what is called 
an electromotive force, <s>and<\s> the two extremities of the body 
tend to become oppositely electrified, and an electric current 
tends to flow through the body. When the electromotive 
force is sufficiently powerful, and is made to act on certain 
compound bodies, it decomposes them, and causes one of their 
components to pass towards one extremity of the body, and 
the other in the opposite direction. 

(9) Here we have evidence of a force, causing an electric current 
in spite of resistance; electrifying the extremities of a body 
in opposite ways, a condition which is sustained only by the 
action of the electromotive force, and which, <s>subsides<\s> as soon 
as that force is removed, tends, with an equal and opposite 
force to produce a counter current through the body, and 
to restore the original electrical state of the body; and finally, 
if strong enough, tearing to pieces chemical compounds, and carrying their components 
in opposite directions, while their natural tendency is to combine, 
and to combine with a force <s>equal and opposite to the<\s> 
<s>electromagnetic<\s> which can generate an electromotive force 
in the reverse direction. 

This then is a force acting on a body caused by its motion 
through the electromagnetic field or by changes occurring in that 
field itself, and the effect of the force is either to produce a 
current and heat the body, or to decompose the body, or when 
it can do neither to put the body in a state of electric polarization 
— a state of constraint in which opposite extremities are oppositely 
electrified, and from which the body tends to relieve itself as 
soon as the disturbing force is removed. 

(10) According to the theory which I propose to explain, this 
"electromotive force” is the force called into play during 
                            
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Manuscript details

Author
James Clerk Maxwell
Reference
PT/72/7
Series
PT
Date
1864
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Cite as

J. C. Maxwell’s, ‘Dynamical theory of the electromagnetic field’, 1864. From The Royal Society, PT/72/7

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