George Biddell Airy to Faraday   28 April 1846

Royal Observatory Greenwich | 1846 April 28

My dear Sir

There is one modification of the magneto-luminous experiment, which, so far as I find in your paper¹, has not been made, but which is theoretically important.

It is simply that the plane of original polarization has not been varied.

When I had the good fortune to see the experiment in your cellar² - first the light was polarized by a reflector whose plane was necessarily fixed - and then it was polarized by Nichol's prism which was not turned during the experiment.

Now would you do me the favour, when your two Nichol's prisms are mounted, to try with four positions of the plane of primary polarization, namely

and examine the amount and direction of the rotation produced by putting in action the magnetic current (no circumstance whatever being varied except the said plane of polarization) and in a single line acquaint me with the result. I am my dear Sir

Yours very truly | G.B. Airy

Michael Faraday Esq | &c &c &c

My sister desires me to say that she has lost the pleasure of attending your last Saturday's lecture³ by absence in Suffolk, but she hopes to avail herself of your kindness now.