Page:The principle of relativity (1920).djvu/19

 of Maxwell's theory. Electric waves behaved generally like light waves of very large wave length.

The orthodox Maxwellian view located the dielectric polarisation in the electromagnetic ether which was merely a transformation of Fresnel's stagnant ether. The magnetic polarisation was looked upon as wholly secondary in origin, being due to the relative motion of the dielectric tubes of polarisation. On this view the Fresnelian convection coefficient comes out to be 1/2, as shown by J. J. Thomson in 1880, instead of 1 - (1/μ^2) as required by optical experiments. This obviously implies a complete failure to account for all those optical experiments which depend for their satisfactory explanation on the assumption of a value for the convection coefficient equal to 1 - (1/μ^2).

The modifications proposed independently by Hertz and Heaviside fare no better. They postulated the actual medium to be the seat of all electric polarisation and further emphasised the reciprocal relation subsisting between electricity and magnetism, thus making the field equations more symmetrical. On this view the whole of the polarised ether is carried away by the moving medium, and consequently, the convection co-*efficient naturally becomes unity in this theory, a value quite as discrepant as that obtained on the original Maxwellian assumption.

Thus neither Maxwell's original theory nor its subsequent modifications as developed by Hertz and Heaviside succeeded in obtaining a value for Fresnelian co-*efficient equal to 1 - (1/μ^2), and consequently stood totally condemned from the optical point of view.

Certain direct electromagnetic experiments involving relative motion of polarised dielectrics were no less conclusive against the generalised theory of Hertz and Heaviside.