John Frederick William Herschel to Faraday   20 December 1845

Collingwood Dec 20 / 45

My dear Sir

Will you bear with me once more if I intrude on your patience with the suggestion of an experiment. I would try it myself - but cannot lay my hands on any glass fit for the purpose and cannot come up to Town to get it properly executed. It is very simple.

AB is a hexagonal prism of glass (or a cylinder with hexagonal or angular ends) whose terminal planes are polished. The lower End is fixed in a block B (ie in a hole pierced in it) to hold it firm. The upper end is jammed in a wrench with handles by which it can be subjected to torsion[.]

Pass a ray of Polarised light from below up thro' it in its natural State and set a Rhomb R above it to analyse the transmitted ray and adjust it to the disappearance or minimum of one image[.]

Then apply torsion, up to the point (if needed) of rupture of the glass[.]

Now I should expect the phaenomenon of Circular Polarisation to arise - as in quartz and to have its right or left handed character according to the direction of the torsion[.]

Believe Me Ever | My dear sir | yours very truly | J.F.W. Herschel

Prof Faraday R.I.

R Institution | 22 Decr. 1845

My dear Sir

I received yours¹ this morning & have already given Newman orders for the glass & that I may make your experiment for you. I perhaps shall not be able to make it for a week or ten days for I am now writing my third paper on the magnetic phenomena² and I shall hardly be able to finish it. This week I must lay all these things down for a fortnight whilst I deliver six lectures that commence next Saturday³[.]

I will make your experiment but in return I must request you to take care of the accompanying paper not opening it but doing with it as I may hereafter direct. I have certain views and amongst them two which if verified people might say were in some way derived from your suggestions. I do not think it likely your experiment will lead you to them nevertheless least it should do so I wish to guard my own position by putting on sure record before hand what are my expectations in these respects. I have long since ordered the apparatus for both but as I said want time and it may be a month or more before I can work them out[.]

I am afraid from the wording of your note that you did not receive my reply from Brighton⁴ to your former letter⁵. I wrote at once.

Ever My dear Sir | Yours Most truly | M. Faraday

Sir J.F.W. Herschell Bart | &c &c &c