Item 28 - James David Forbes to William Whewell

4 pp

Edinburgh - JDF observed the eclipse on Sunday with Murchison [Roderick Murchison]. JDF made it the occasion of trying out an experiment to test David Brewster's hypothesis regarding the solar spectrum. According to DB's theory the solar spectrum lines are a product of the sun's own atmosphere: 'if so, the edges of the sun which afford light which must have traversed a much greater thickness of the sun's atmosphere should shew an infinity of lines which are filled up by the more complete light derived from his central parts'. JDF found no difference in the solar spectrum during and after the eclipse, hence this theory of absorption will not hold: 'I presume that the sun's light (like that of the Electric spark etc) is primitively deficient'. JDF thinks that an interesting point worth developing would be to look at 'the variation in the kind and quantity of proof required as demonstration by the human mind in different ages'. Edinburgh University is in need of some good candidates for the Logic Chair - 'I wish you could send us some'. JDF is glad 'you have got some new supporters of the undulatory theory'.