While it's known that the speed of electric current signals in a conducting wire is very close to the speed of light, it is not generally known why these two phenomena, which appear to be quite distinct physically, should share a common speed. It seems though that the answer was already known in the 1930s, yet forgotten about after the war. The 1937 Encyclopaedia Britannica article, "Ether (in physics)", states, in relation to the speed of light,
“The most probable surmise or guess at present is that the ether is a perfectly incompressible continuous fluid, in a state of fine-grained vortex motion, circulating with that same enormous speed. For it has been partly, though as yet incompletely, shown that such a vortex fluid would transmit waves of the same general nature as light waves— i.e., periodic disturbances across the line of propagation—and would transmit them at a rate of the same order of magnitude as the vortex or circulation speed”
This picture is not far removed from the physical model that James Clerk Maxwell used in the nineteenth century, from which he derived his famous equations of electromagnetism, and more than one hundred years before that, the younger John Bernoulli proposed a similar model to account for some optical phenomena. This article here examines much of the related material. "The Commonality between Light and Electric Current",
https://www.researchgate.net/publication/364337354_The_Commonality_between_Light_and_Electric_Current
