Copy letter, from Sir John Herschel to William Henry Fox Talbot, dated at Slough Copy letter in John Herschel's hand. Admires L. J. M. Daguerre's process, but hopes to see paper become dominant medium for photographs. Describes new paper John Frederick William Herschel developed. [Letter continues 6 July.] Experiment with fixed lines in chemical spectra; shows sensitivity of ultraviolet light. 24 June 1839