Jonathan Pereira to Faraday   7 November 18451

47 Finsbury Square | November 7th 1845.

My dear Faraday

Regularly formed crystals of alum & rock salt are equiaxel & have no double refraction. Occasionally irregularly formed crystals of these substances are met with which, in the polariscope, exhibit traces of a doubly-refracting structure2.

Believe me, my dear Faraday, | ever yours faithfully | John Pereira

M. Faraday Esq.

1
Jonathan Pereira (1804-1853, DNB). Pharmacologist.
2
Faraday needed this information to confirm his view that only singly refracting crystals displayed the magneto-optical effect. See Faraday (1846b), ERE19, 2177 and letter 1784.

Bibliography

FARADAY, Michael (1846b): “Experimental Researches in Electricity. - Nineteenth Series. On the magnetization of light and the illumination of magnetic lines of force”, Phil. Trans., 136: 1-20.

Please cite as “Faraday1781,” in Ɛpsilon: The Michael Faraday Collection accessed on 29 April 2024, https://epsilon.ac.uk/view/faraday/letters/Faraday1781