263 Strand

12 July 1836

D^r Sir

I herewith forward a Tourmaline ^<1> mounted to order and hope it will meet your approval it is a fine stone but rather small tho’ large enough if placed close to the eye –

Yours very truly

Andrew Pritchard

To H. F. Talbot Esq^re

To a fine small Tourmaline mounted 0. 9. 0

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Notes:

1. He was using the principle of the polariscope to examine the interference colours produced when the two rays of polarised light are recombined into the same plane, at the analyser (the tourmaline in this case).