Thanks RH for his 'extensive and instructive view on the present state of photography.' Found many interesting results in experimenting with vegetable substances. Surprised by RH's discovery that bi-chromate of potash is a photographic substance; JH nearly achieved this result.

Returns with grateful thanks the example of photographs recently sent him. They open up a new field of curious processes. Will not have much time this summer for photographic experiments as he is carrying out a series of investigations into the air of mines. Has been experimenting with the cyanurets.

Believes that the operative rays in JH's thermographic process are neither 'calorific' nor 'thermal'.

Some information about Charles Piazzi Smyth. JH needs information about some of RH's photographic paper, which JH has tried but without success.

Was hoping to send him some positive paper, but has been unable to prepare this due to a medical problem. Did make a sheet or two today. Returns some of the specimens JH sent him but would like to keep those made by JH himself.

Sorry to hear RH has been ill; JH sends some photographic examples.

Thanks for RH's paper on mineralogy. JH has explored use of mercury together with iron in photography.

Is grateful for the specimens sent him. Has been carrying out a series of experiments on the Calotype process with extraordinary results, especially the crimson skies. What does he think of the idea of publishing a treatise on 'Light' considered as a chemical agent?

Has been working at [L. F.] Moser's experiments and believes he is wrong in considering latent light as the agent that produces the photographic image. Read a paper last evening on the subject, which will be printed. Has been producing images by the action of heat and electricity and proposes to call this process Thermography.

Was pleased to receive JH's letter and to read that he had really proved the existence of [invisible light?]. One of his students has produced images on copper plates by sulfur fumes. Has just seen Macedoine Melloni's memoir, which is now governed by JH's views.

Sends RH a packet of photographs with a description of each type.

Was very pleased with the specimen JH sent him; it is still in good condition. Has he read [John William] Draper's paper? Comments on some of the points. Outlines some of his own proposed experiments.

Is anxious for some means to be developed to get a measurable quantity [preferably by weight] from the action of a beam of light on a surface. JH has been experimenting in photography with 'flouric' compounds.

Read John William Draper's papers; although he believes that Draper's instruments are inconsistent, JH feels that they are still important because they are measurable. Decries [L. F.] Moser's skepticism of photography's value, calling it a 'blindfolding to some of the most interesting physical relations that have ever been discovered.'

Much indebted for his paper on the influence of the solar spectrum on vegetable colors. Has a series of experiments ready that he hopes will resolve some of his own doubts. Does not like the term J. W. Draper uses for the new rays.

Sends a few samples of plates made by the cyanotype process; they are poor because the sun has not been very strong of late. Comments on this process and wishes JH would make a few experiments with his more perfect apparatus. Inclined to agree with him about the mechanism of the eye.

Has been reading JH's communication to the P.M. [on solar spectrum] and wishes to point out that RH was the first to carry out those experiments, which are recounted in the P.M. for 1840.

Clarification of priority to the prismatic analysis of the Daguerreotype photograph; comments on the location of a limiting diaphragm in a camera obscura.

Enlarging on the luminous phenomena he has seen in the S.W. and giving some comments from a naval officer who had observed it.

Some comments about photographic processes and about RH's observations of the heavens [see RH's 1843-3-24].