Writes to say that the point on which he thought GHD’s drawings were mistaken proves to be an error in his own observation.

He and Emma rejoice that GHD’s mathematical troubles are at an end. It is miraculous that he unconsciously followed the right course – like composing a sonata by a fluke.

Recounts the experiments on Fechner’s law he has found in Helmholz; they are on the smallest perceptible differences of illumination. Describes how to test whether plants’ responses to lights are in accordance with it.

Rejoices that he should have "staggered" William Thomson so quickly and that the latter should speak of GHD’s "discovery". The internal heat [of the earth] will please geologists and evolutionists.

Delighted with [William Thomson’s] report. "There can be no doubt now about the value of your work." CD has "not been so much pleased for a long time".

Asks CD if he would screw himself up to inviting A. Newton to Down.

Encloses William Thomson’s report on GHD’s paper. Some of it was written in Rayleigh’s hand.

No summary available.