TALBOT213

65. Harley S^{t 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 D^r 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 S^t