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].

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.

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?

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.