Einstein and the Changing World Views of Physics, 1905/2005

HGR7. Seventh International Conference on the History of General Relativity,
La Orotava, March 9-15, 2005

 

Relativity: the Roots

Jean Eisenstaedt

Observatoire de Paris

In 1786, Robert Blair, an unknown astronomer from Edinburgh, gave a systematic treatment of a -classical and relativistic- Newtonian kinematics of light.
Two years before, John Michell had developped a Newtonian theory of the action of gravitation on light, and invented what Laplace later called dark bodies. In the same way Soldner will calculate the deviation of light due to gravitation. Michell had also pointed out that the velocity of light could be measured with the help of refraction experiments and put forward the essence of the Einstein Doppler gravitational effect.
Blair went a step further and inferred the existence of the Doppler-Fizeau effect : a variation of refraction due to a relative motion of the source and the observer. He clearly understood that it was a way to determine the motion of the Earth, planets and stars. Blair's proposal is at the roots of Arago's well-known 1806-1810's experiments on the velocity of light.
In the context of the undulatory theory of light, he also proposed an experiment to determine the absolute velocity of the Earth, actually the basis of the famous experiment performed by Albert Michelson 100 years later.
In fact, this corpus contains the very questions of the relativistic optics of moving bodie, the roots of spectroscopy, and addresses the very problems that would be hotly debated in the 19th century, only to be solved by Einstein in 1905.