Is gratified that JM is taking an interest in double stars. Comments on some of the observations and time of their orbits.

Plans to calculate Gamma Virginis orbit. Received WS paper on astronomical observations. Suggests WS look for a house in Kent after learning plans to move near London.

Instructions for preparing liquid for the actinometer. Describes 'very strange' experiments on the spectrum as well as an 'unusual' cloud formation.

Sends GA a spectrum photograph, and explains how JH obtained it.

[JH's outline of letter] Compares Wilmot's actinometer observations with JH's. Acknowledges receipt of St. Helena specimens.

Impressed by accuracy of actinometer measurements made by JK, Joseph Dayman, and P. A. Scott from Feb. to Sept. 1841 at JK's observatory at Rossbank [Tasmania]. Suggests methods to improve readings and simplify reductions.

Thanks for calotypes involving persons engaged in actions. Gives encouragement to WT's planned photographic tour in Germany. JH has been experimenting regarding color photography.

Sends GA two more spectrum photographs [see JH's 1842-4-10], and believes that these may lead the way to color photography.

Stresses importance of development and phases of periodic phenomena on earth's surface. Magnitudes of stars are the only observations JH is doing. Asks for help in planning trip on continent for three of his daughters and their governess.

Proposes meeting times in town. Suggests that JF observe the upcoming total eclipse astronomically. Agrees with JF's seemingly 'cold &c' circular on scientific partnerships, while regretting that it needed to be written.

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

Sets up approximate meeting time, depending on his family's timely departure to Antwerp, with JF at the R.S.L. apartments.

Thanks for assistance in preparing trip. JH's daughters will probably not stay in Brussels long. Mentions his first engraving for Cape observations of nebulae is to be engraved this very day. Three quarters of his reductions of the southern sweeps are completed.

Thanks WS for C. P. Smyth drawings of Cape monument and Gamma Virginis observations. Notes J. H. Mädler's work on double stars and the doubt that they obey the inverse square law. Discusses use of photography in astronomy.

Discusses JH's spectrometer and possibility of using surplus from R.S.L. Donation Fund for its construction and enquiry with it into nature of light and heat.

Offers to meet FB at Manchester B.A.A.S. meeting and to bring FB to Collingwood for a quiet visit.

Has stayed in Manchester an extra day, and has managed to avoid becoming involved in the organization of next year's B.A.A.S. meeting at Cork; talks about plans for F. W. Bessel to visit Collingwood, and about JH's plans to return home.

Alerts WW that F. W. Bessel, in very poor health, will attend the Manchester B.A.A.S. meeting. JH plans to bring Bessel to Collingwood after the meeting.

Compares actinometric measurements of radiation. Explains interest in total eclipse relative to actinometry. Discusses the possibility of making actinometric measurements by photographic means.

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