The Full Significance of the Speed of Light
In the year 1855, German physicists Wilhelm Eduard Weber and Rudolf Kohlrausch performed a landmark experiment of profound significance. By discharging a Leyden jar (a capacitor), they linked the speed of light to the ratio between electrostatic and electrodynamic units of charge. This experiment was electromagnetism’s Rosetta Stone because the result can be used to, (i) identify the speed of light as the speed of circulation of electric current, (ii) identify the speed of light as the speed of electromagnetic waves through a dielectric solid that pervades all of space, while noting that inertial centrifugal force and dipole fields share in common an inverse cube law in distance. The result can also be used to, (iii) identify magnetic repulsion as a centrifugal force, and hence to establish the double helix pattern that characterizes magnetic lines of force.