Tells WT about JH developing the thermographic paper which is susceptible to 'calorific' and 'chemical' rays of light.

Comments on the affidavit supplied by WT; will sign most of it but objects to one section.

Clarifies JH's position, by saying that he clearly supports WT as the inventor of the calotype or talbotype, but has reservations about the collodion process.

Sent WT's specimens to J. B. Biot and F. J. D. Arago in Paris. Developed paper sensitive to heat rays of sun 'beyond the spectrum.' Diagram of three spectra: 'luminous, chemical, and thermic.'

Considerable comment on procedure for submitting paper to R.S.L. Urges WT to mention JH's method of washing with hyposulfite. Comments on some photographic experiments of WT.

Expresses reservations about Samuel Brown's work. Apologizes for delay in trying calotype; has done only some vegetable substance trials.

Thanks for specimen of light sensitive paper. Provides hint on the chemical process that Louis Daguerre may have used in his photographic work. Sends specimens of JH's own work.

Describes method of varying the size of photographic images. Praises Talbot's light sensitive paper and suggests improvements regarding it. Complains about persons too ready to seek a patent.

[Responding to WT's 1826-2-7], JH thanks WT for materials sent, makes suggestions regarding WT's upcoming trip to Geneva, and asks WT to deliver a book to [Alfred] Gautier.

[Responding to WT's 1826-3-24], JH concurs with P. S. Laplace's view about the advantage of astronomical observation from high elevations, e.g., from mountains. Comments on telescope prices, a paper by WT, Florence, and JH's plan to visit the Continent.

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.