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The Diagonal Opera Glass


By the diagonal position of a plane mirror, a curious opera-glass is

constructed, by which any person may be viewed in a theatre or public

company without knowing it. It consists only in placing a concave

glass near the plane mirror, in the end of a short round tube, and a

convex glass in a hole in the side of the tube, then holding the end

of the tube with the glass to the eye, all objects next to the hole in

the side will be reflected so as to appear in a direct line forward,

or in a position at right angles to the person's situation who is

looked at. Plane glasses, instead of a convex and concave, may be

used; in this case the size of the object will not be increased, but

it will appear brighter.



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