A measurement of the kind referred to was executed in 1849 by Fizeau (born at Paris in 1819).
Fizeau, from experiments which he conducted on running water, also came to the same conclusion.
If we examine Fizeau's apparatus closely, we shall recognise in it an old acquaintance: the arrangement of Galileo's experiment.
The only positive result ever supposed to be attained was in a very difficult polarisation observation by Fizeau in 1859.
This experiment has now been made in a highly refined form by Fizeau, and repeated by M. Cornu with prodigious care and accuracy.
