Abstract

In 1786, Robert Blair, an unknown astronomer from Edinburgh, wrote a paper that would remain unpublished. In his manuscript, Blair gives a systematic treatment of the Newtonian kinematics of light, taking into account in the absolute space of Newton the motion of the light source, that of the observer, and the velocity of the corpuscles of light. Two years before, in the context of Newton's corpuscular theory of light, John Michell had pointed out that the velocity of light could be measured with the help of refraction experiments. Blair went a step further and inferred the existence of what we now call the Doppler effect: a variation of refraction due to a relative motion of the source and the observer. Blair's proposal is at the roots of Arago's well‐known 1806–10 experiments on the velocity of light. In the context of the undulatory theory of light, Blair proposed an experiment to determine the absolute motion of the Earth, laying the bases for the famous experiment performed by Albert Michelson 100 years later. In fact, this manuscript contains the very questions of light relativity, the roots of spectroscopy, and addresses the very problems that would be hotly debated in the nineteenth century, only to be solved by Einstein in 1905