George Biddell Airy to Faraday   25 May 1846

Royal Observatory Greenwich | 1846 May 25

My dear Sir

I return in a separate package by Post (so arranged that, I hope, it will receive no injury) the equivalent quartz plate¹, and in this I offer you my thanks for the opportunity of trying it. The thickness I find is about 0in.053. But I think it probable that the equivalency applies to only one colour. For, it seems to me, the magnetic arrangement separates the colours less than the quartz. But I wish that measures were made in reference to this chromatism.

I have sent to R. Taylor two papers concerning you. One is on the mathematics of the magnetical twisting²: and it is as dull as other mathematics. The other³ is a comment upon your radial paper⁴: dissenting much, but, I hope, in a style which will not be disagreeable to you.

I am, my dear Sir, | Yours most truly | G.B. Airy

Michael Faraday Esq | &c &c &c