Relation between Electric <s>Condu<\s> Resistance and Transparency (106) If the medium, instead of being a perfect insulator is a conductor whose resistance per unit of volume is [rho] then there will be not only electric displacements but true currents of conduction in which electrical energy is transformed into heat and the undulation is thereby weakened. To determine the coefficient of absorption let us investigate the propagation along the axis of x of the transverse disturbance G By the former equations d<sup>2<\sup>G/ dx<sup>2<\sup> =  4[pi][mu](H') = —4[pi][mu](df/dt + q) by (A) d<sup>2<\sup>G/dx<sup>2<\sup> = + 4[pi][mu](1/k d<sup>2<\sup>G/dt<sup>2<\sup>  1/[rho] dG/dt) by (E) & (F) (95) If G is of the form G = e<sup>px<\sup> cos (qx + nt> (96) we find that p = 2[pi][mu]/[rho] n/q = 2[pi][mu]/[rho] V/i (97) where V is the velocity of light in air and i is the index of refraction The proportion of incident light transmitted through the thickness x is e<sup>2px (98) Let R be the resistance in <s>absolute<\s> electromagnetic measure of a plate of the substance whose thickness is x, breadth b and length l then R = l[rho]/bx 2px = 4[pi][mu] V/2 l/bR (99)
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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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