Typo: A Monthly Newspaper and Literary Review, Volume 3
Several times we have made reference to the ingenious optical illusions devised at Messrs Field and Tuer's Leadenhall Press. Some of these, used as advertisements of Pears' soap, have gained world-wide celebrity. By the kindness of Mr A. Tuer, of the Paper and Printing Trades Journal, who has sent us the blocks, we are able to reproduce the best and most recent of these designs. They are all based on well-known optical laws.
The first demonstrates the existence of a minute blind spot in every eye. As they are differently situated right and left, they do not impede vision, and can only be detected by some such experiment as this:—Close one eye, and look steadily at the eye of the Sphinx farthest from your open one, taking care that the eyes of the figure are opposite your own. Though looking with one eye only, you will see both. Bring the diagram steadily nearer your face, and one of the eyes will vanish.
Judging by the eye alone, most people will answer these questions wrongly:—