JT has suggested that JH's son [Alexander] be appointed to position in Royal School of Mines, but colleagues, unwisely, JT thinks, want someone more well-known.

Asks JT to distribute some circulars about the work of Gustavus Hinrichs of Iowa, whom CD wishes to help.

Admires JT’s Norwich address [to Mathematics and Physics Section, BAAS meeting, Rep. BAAS 38: 1–6] and his Fortnightly Review paper on scientific discovery [7 (1867): 645–60].

Gustavus Hinrichs is also a [not highly regarded] correspondent of JT’s; he will put GH’s papers on the table at Royal Institution to ease CD’s conscience.

Dined with the Asa Grays at Hooker’s. Told Mrs Gray that CD’s ill health was a benefit because it caused him to ponder a great deal.

Invites JT to come to Down with the Asa Grays and Hookers.

Thanks for paper on action of solar and electric light on vapors, which should give JT further insight into blue color of sky and polarization of skylight. Comments on the latter. JH's son [Alexander] is working hard at Glasgow.

Is studying vesicles. JH's son [Alexander] may yet get Royal School of Mines appointment.

Observations on subjecting carbonic acid to concentrated beam of an electric lamp. Records experimental result so far. Interested in ordinary dust particles under electric light.

Continues experiments with carbonic acid and electric light [see JT's 1868-11-30], hoping to 'explode' idea that atmosphere's polarization is due to reflection by air particles.

Thinks JT's work on polarization will lead to remarkable discovery. Discusses production of rainbow, parallels to Isaac Newton's explanation of black spot on a soap bubble, and problems in JT's undulatory theory explanation of reflection. In JT's experiments, what are nebulous particles produced by light in gas or vapor?

Continues experiments with carbonic acid and electric light [see JT's 1868-11-30], suggesting possible cause of blue cloud color and eventual whitening of light.

Asks JH to review paper on blue color of sky, polarization of skylight, and polarization of light by cloudy matter.

JT's paper on polarization of sky light suggests that neutral points are functions of cloud density. This verifies JH's earlier explanation of blue sky color. Incomplete polarization. Cause of blue color in water. Corrects note on W. A. Miller's observations of rainbows.

Thanks for paper verifying JH's prediction that explanation of blue sky color carries with it that of polarization of skylight. Involves ultimate link between chemical and analytical dynamics. Notes that 'neutral points' in sky polarization have yet to be explained; offers tentative explanation based on clues in JT's work.