Perhaps some one in the company has made use of the saying that he “can see as far through a millstone as anybody.”
Eagerly espouse his cause, and declare him, indeed, gifted with preternatural vision, as you will prove to him by your magic spyglass.
A box is made with two upright extensions, in which are placed the tubes of telescopes, with plain glass eyepieces. A A A A are plane mirrors, set all at an angle of 45 degrees, so that any one looking in at either end, sees whatever is visible at the other extremity.
Fig. 137.
THE POLEMOSCOPE.
This is an utilisation of the last-mentioned trick.
If the higher glass is placed behind the other, or even with its sides parallel with its own, the latter could be behind an impenetrable wall to shelter the observer, without the landscape being out of the scope of vision.
Another plan is to place the upper mirror without a window above the house-door, to reflect the part of the street beneath upon a mirror within on the sill.
A third is in miniature, by which an opera-glass has an opening at the side of the barrel, by which one’s neighbours are scrutinized while, to all appearance, one is intently examining the performers. Happily the frequenters of the playhouse of the present day are less sensitive than our forefathers, and no such deceptions to avoid showing impoliteness are in request.