Mr. Weaber, an optician, of Oxford Street, has invented a
clever little instrument which will prove of great value to all who wear spectacles. All good spectacles are now made of pebbles, which do not scratch like glass, and are more free from flaws, but all pebbles are not good ones. This little instrument, which we have tested, though without understanding it, makes the quality of the pebble at once apparent to the eye. If the lens placed in it is glass the spectator cannot see through it at all, if a good pebble he can as through an even piece of topaz, but if bad his eye is distracted by all the colours of the prism. The multitude of little angles in a bad lens worry and strain the eye, as anybody can see who will look patiently for a minute through an ordinary window pane, usually the very worst piece of glass it is possible to make.
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