British Association for the Advancement of Science · London, Anthropological Institute · leaf 76
44 of eyesight is the greatest distance at which a square of known size that has two of its sides vertical as in fig. i, can be … Fig. i. Fig. 2. distinguished from another of the same size that has one of its diagonals vertical as in fig. 2. These two figures represent the opposite faces of the same card (or of painted zinc, which would be more durable), which is intended to be hung against a rather dark background. Procure…
