65. Harley St <1>
Wednesday Evening
Dear Sir
I am extremely obliged to you for your reference to the description of the Actinometer, <2> the more so that Dr Lindley <3> had previously inquired of several scientific persons without success –
I have thought of a method of measuring the refrangibility of definite rays, which I think cannot fail of possessing sufficient accuracy and facility – If you will make the homogeneous rays I will have the instrument constructed, so as to give it a fair trial –
Yours very truly
H. F. Talbot
C. Wheatstone Esq
20 Conduit St
Notes:
1. Harley Street, London.
2. Actinometer, an instrument for measuring the intensity of light. The term was coined by Sir John Herschel in ‘Additional Observations on Leslie’s Photometer, &c By William Ritchie, A.M. Rector of the Academy at Tain. In a Letter to Dr Brewster’, Edinburgh Journal of Science,v. 3, 1825, pp. 104–107).
3. Prof John Lindley (1799–1865), botanist.