Collingwood <1>
29 February 1848
My dear sir
You will find Fraunhofers theorem <2> proved & almost every other possible Gitter <3> phenomenon worked out most completely by Schwerd in his “Beugungserscheinungen”
(Manheim 1835
Schwan & Goetz) <4>
and compared with experiment. It is a very excellent work & the mode of treatment of elementary simplicity. But before you therefore decide how far your theory is anticipated you had better look at the work.
I am sorry I have not had time to write before in answer to your note wh I am horrified to see bears date Feb 4. <5> Pray excuse me. I have much on my hands which has no connexn with Science and am moreover kept hard at work in Scientific matters not of my own chusing and so prevented from working at subjects of my own choice among wh the chief would be physical optics – but alas! Optical experiments shall I never I fear be able to make more!
Believe me My dear Sir Yours very tly
JFW Herschel
H.F Talbot Esqr
Notes:
1. The Herschel family home in Hawkhurst, Kent.
2. Joseph von Fraunhofer (1787–1826), optician, Munich.
3. Although ‘gitter’ can mean a mathematical ‘lattice’, Herschel intends its other meaning here, that is ‘grating’.
4. Friedrich Magnus Schwerd (1792–1871), Die Beugungserscheinungen aus den Fundamentalgesetzen der Undulationstheorie (Mannheim: Schwan and Goetz, 1835).
5. This is Doc. No: 06099, where WHFT discusses Fraunhofer's theorem.