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

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                                according to the more accurate experiments of M Foucault 

V* = 298 000 000 

Velocity of light in the space <s>behi<\s> surrounding the earth, deduced 
from the coefficient of aberration and the received value of 
the <s>distance<\s>radius of the earths orbit 

V = 308,000,000 

Weber & Kohlrausch's number will probably 
be corrected considerably by the B of [unclear] of [unclear] 

(97) Hence the velocity of light deduced from experiment agrees 
sufficiently well with the value of v deduced from the only set 
of experiments we as yet possess. The value of v was determined 
by <s>discharging<\s> measuring the electromotive force with which 
a condenser of known capacity was charged and then discharging 
the condenser through a galvanometer so as to measure the 
quantity of electricity in it in electromagnetic measure. The only 
use made of light in the experiment was to see the instruments 
The value of V found by M Foucault was obtained by determining 
the angle through which a revolving mirror turned while the light 
reflected from it went and returned along a measured course 
No use was made of electricity or magnetism whatever. 
The agreement of the results seems to show that light and 
magnetism are affections of the same substance and that 
light is an electromagnetic disturbance propagated through the field 
according to electromagnetic laws. 

* Comptes Rendus vol LV (<s>Nov 24<\s> 1862) pp501. 792 

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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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