George Walford: NIAT (63)

More than one correspondent has brought against NIAT the counter-example of the velocity of light, held to be not merely an absolute but a scientific one. IC has responded by pointing out that this uses ‘absolute’ in a different sense from NIAT, a more limited sense which amounts to hardly more than ‘invariant.’ It now appears that the velocity of light may not be absolute even in that weak sense. Consider this:

In 1859 Hippolyte Fizeau published, in Annales de chimie et de physique, a fine experiment which ‘showed that the velocity of light increases in a medium according to the formula: v (1 – 1/n2) where v is the velocity of the medium, and n its refractive index.’ [1]

If the velocity of light varies with the medium, then the claim even for its invariance does not stand up. Would any reader enjoying familiarity with these matters care to comment?

[1] C. G. Gillispie 1960, The Mechanization of the World Picture, Princeton etc.: OUP, 427.

from Ideological Commentary 63, February 1994.