Thanks WT for bringing to JH Josef Fraunhofer's publications and Franz Gruithuisen's plates. Recounts JH's geologizing in France and JH's efforts to measure solar radiation.

Thanks WT for optical equipment sent. Notes death of Augustin Fresnel. Has purchased a telescope from James South.

Responds to WT's 1827-10-29. Sending JH's Light, which uses some of WT's publications.

Asks about a servant JH is considering hiring to accompany JH on JH's trip to the Continent.

Sending WT some seeds. Had hoped to send some bulbs.

Is sending WT some botanical specimens through Andrew Smith, whose scientific abilities JH praises. Asks WT to assist Smith in England. Encourages WT's work in mathematics and in 'photology.' Reports on JH's astronomical observations and theorizes about sunspots.

Says that for the next four to five months will be in residence at 10 Hanover Crescent, Regent's Park. Offers various botanical specimens to WT, including a Satyrium named after JH. Mentions Eta Argus. Believes the 'Southern Sky has been pretty well rummaged.'

[Responding to WT's 1839-1-25], JH reports that he cannot come to London to see WT's 'curious process of fixing the image formed by a Camera obscura.' Invites WT to come to Slough.

[Responding to WT's 1839-1-29], urges WT to find some way of giving at least slightly different papers to R.S.L. and Athenaeum. Comments on process of fixing image, referring to a trial of his own.

JH welcomes WT's mentioning JH's method of fixing with hyposulfite. JH has put some of JH's images on display at R.S.L. Mentions JH's recent experiments relating to photography. Comments regarding a paper submitted to R.S.L. by WT and on some experiments of WT.

JH will as WT requests stop mentioning JH's hyposulfite fixing process and await publication of WT's process. Reports in detail on some of JH's experiments relating to photography and to spectrum analysis. [In a P.S. dated 1839-2-13,] JH states: 'I have discovered your secret of fixing [or its] equivalent.'

Invites WT to mention JH's hyposulfite process to J. B. Biot. Recounts JH's recent experiments.

Thanks for specimens of [light] 'sensitive paper.' Praises it. JH has handed over all his specimens of photography to R.S.L. Recommends a paper by the chemist Henri Regnault.

Thanks for photographic specimens WT sent. Reports on JH's recent experiments, including some using lenses, in photography; comments on WT's experiments and on the process of patenting.

Comments on several approaches to fixing images on paper, especially using pure water as a fixing agent. Has developed a new sensitive paper but is keeping it secret until perfected. Is leaving for Continent on 1 May.

JH reports his discovery of a highly sensitive paper. Tint continues to deepen with time, as bromine does not. Not prepared to reveal process at present. Is off to Paris.

Just visited L. J. M. Daguerre. Praises his images as 'miraculous' and also Daguerre's times of exposure. Daguerre puts his images on 'thin sheets of plated copper.'

Admires L. J. M. Daguerre's process, but hopes to see paper become dominant medium for photographs. Describes new paper JH developed. [Letter continues 6 July.] Experiment with fixed lines in chemical spectra; shows sensitivity of ultraviolet light.

Recounts experiments with chemicals, spectra, and photographic paper.

Has succeeded in producing a 'photograph on glass.' Describes process and also JH's experiment photographing spectra.