“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.

“The properties of these spectacles introduce a very curious and interesting feature into the case.  To the majority of persons, the wearing of spectacles for the purpose of disguise or personation, seems a perfectly simple and easy proceeding.  But, to a person of normal eyesight, it is nothing of the kind.  For, if he wears spectacles suited for long sight he cannot see distinctly through them at all; while, if he wears concave, or near sight, glasses, the effort to see through them produces such strain and fatigue that his eyes become disabled altogether.  On the stage the difficulty is met by using spectacles of plain window-glass, but in real life this would hardly do; the ‘property’ spectacles would be detected at once and give rise to suspicion.

“The personator is therefore in this dilemma:  if he wears actual spectacles, he cannot see through them; if he wears sham spectacles of plain glass, his disguise will probably be detected.  There is only one way out of the difficulty, and that not a very satisfactory one; but Mr. Weiss seems to have adopted it in lieu of a better.  It is that of using watch-glass spectacles such as I have described.

“Now, what do we learn from these very peculiar glasses?  In the first place they confirm our opinion that Weiss was wearing a disguise.  But, for use in a room so very dimly lighted, the ordinary stage spectacles would have answered quite well.  The second inference is, then, that these spectacles were prepared to be worn under more trying conditions of light—­out of doors, for instance.  The third inference is that Weiss was a man with normal eyesight; for otherwise he could have worn real spectacles suited to the state of his vision.

“These are inferences by the way, to which we may return.  But these glasses furnish a much more important suggestion.  On the floor of the bedroom at New Inn I found some fragments of glass which had been trodden on.  By joining one or two of them together, we have been able to make out the general character of the object of which they formed parts.  My assistant—­who was formerly a watch-maker—­judged that object to be the thin crystal glass of a lady’s watch, and