27th March 1862
Dear Sir,
Your experiment is an excellent one;—so good indeed that I am disposed to have your letter2 sent to the Philosophical Magazine for publication.3
You remember the hollow & the solid frustum of a pyramid which I referred to in my lectures.4 The upper section of the frustum changes in apparent area exactly as your norm changes.
Your solution has been already revealed by Sir David Brewster—but your treatment is evidently quite original & does you very great credit
I am dear Sir | Yours very faithfully | John Tyndall
Royal Society MM/9/19
Richard Thomas Lewis: (1839–1916), amateur microscopist, entomologist and temperance advocate. See Emily J. Lewis, ‘Obituary notices: Richard Thomas Lewis FRMS’, Journal of the Quekett Microscopical Club, 13 (1916–18), pp. 201–03.
your letter: see letter 1871.
sent to the Philosophical Magazine: appeared as R. Lewis, ‘On the changes in the apparent size of the moon’, Phil. Mag., (1862) pp. 380–82.
in my lectures: Lewis was attending Tyndall’s ten lectures on light delivered at the Royal School of Mines, starting 22 February 1862. It was the lecture on 16 March that prompted Lewis to write to Tyndall. See letter 1871.
Please cite as “Tyndall1872,” in Ɛpsilon: The John Tyndall Collection accessed on