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Observatory - There is not a word about undulations in the papers by William Herschel on Newton's rings, in the Philosophical Transactions for 1807 and 1809 respectively: 'I have been observing the following curious phenomenon. If Newton's rings be produced by two glasses, however they be viewed the central spot is black. But if a glass be placed on metal, and viewed with polarised light (polarised to plane of reflection) then up to the polarising angle the central spot is black, and instantly beyond that it is white. This I anticipated from Fresnel's [experiments]: it is confirmatory of them, and defies emissions'.