Off-topic but I'll take the opportunity to paste my favorite Maxwell quote (from James Clerk Maxwell, A Treatsie on Electricity and Magnetism, 1873): "In the p

Off-topic but I'll take the opportunity to paste my favorite Maxwell quote (from James Clerk Maxwell, A Treatsie on Electricity and Magnetism, 1873): "In the present state of science the most universal standard of length which we could assume would be the wave length in vacuum of a particular kind of light, emitted by some widely diffused substance such as sodium, which has well-defined lines in its spectrum. Such a standard would be independent of any changes in the dimensions of the earth, and should be adopted by those who expect their writings to be more permanent than that body."