“To return to Weiss. He was clearly heavily disguised, as we see by his unwillingness to show himself even by the light of a candle. But there is an item of positive evidence on this point which is important from having other bearings. It is furnished by the spectacles worn by Weiss, of which you have heard Jervis’s description. These spectacles had very peculiar optical properties. When you looked through them they had the properties of plain glass; when you looked at them they had the appearance of lenses. But only one kind of glass possesses these properties; namely, that which, like an ordinary watch-glass, has curved, parallel surfaces. But for what purpose could a person wear ‘watch-glass’ spectacles? Clearly, not to assist his vision. The only alternative is disguise.