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

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                                (107) Most transparent solid bodies are good insulators 
whereas all good conductors are opaque. 
Electrolytes allow a current to pass easily and yet are 
often very transparent. We may suppose, however, that 
in the rapidly alternating vibrations of light, the electromotive 
forces act for so short a time that they are unable to 
effect a complete separation between the particles in 
combination so that when the force is re<s>f<\s>versed the particles 
oscillate into their former position without loss of energy. 

Gold, Silver and Platinum are good conductors and yet when reduced to sufficiently thin plates they allow light to pass 
through them. If the resistance of gold is the same 
for <s>the<\s> electromotive forces of short period as for those with 
which we experiment, the amount of light which 
passes through a thickness of 1/282000 inch would be only 
10<sup>-300<\sup> of the incident light, a totally imperceptible quantity. 
I find that between 1/500 and 1/900 of <s>the<\s> green light gets through 
such gold leaf. This result cannot be reconciled with 
the electromagnetic theory of light unless we suppose 
that there is less loss of energy when the electromotive forces 
are reversed with the rapidity of the vibrations of light, than 
when they act for sensible times as in our experiments. 

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James Clerk Maxwell
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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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