Turning this question over, I suddenly remembered the peculiarity of Mr. Weiss’s spectacles. And here I met with a real poser. I had certainly seen through those spectacles as clearly as if they had been plain window-glass; and they had certainly given an inverted reflection of the candle-flame like that thrown from the surface of a concave lens. Now they obviously could not be both flat and concave; but yet they had the properties peculiar to both flatness and concavity. And there was a further difficulty. If I could see objects unaltered through them, so could Mr. Weiss. But the function of spectacles is to alter the appearances of objects, by magnification, reduction or compensating distortion. If they leave the appearances unchanged they are useless. I could make nothing of it. After puzzling over it for quite a long time, I had to give it up; which I did the less unwillingly inasmuch as the construction of Mr. Weiss’s spectacles had no apparent bearing on the case.