Discusses how exceptional observations of meteorological and magnetical phenomena should be recorded and what significance should be attached to them. Cannot attend next meeting of committee.

Thanks GA for exercising GA's usual discretion in the matter of the funding of Charles Babbage's calculating machine [see GA's 1842-9-26].

Proposes to come to London to visit him. Has just received the proofs of Robert Maine's paper on parallax.

Remarks that he is 50 years old, and that he and CH have 'seen something of that odd and most changeable compound called Human Nature.'

Arranging a visit for GA to Collingwood.

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

Final arrangements for GA's visit to JH [see GA's 1842-3-15].

Responds to RM's request for an analysis of the cause of the difference in climate between Orenburg and Catherineburg in Russia. Agrees that Geological Society can print JH's Alpine memoir.

Comments on WL's finding a sixth star in the trapezium of Orion [see WL's 1842-3-10]; lists other catalogues that identify that star.

Appreciates receiving the curious fossil, even though JH knows little of such matters.

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.