43 
The following questions may also be answered (blit due 
allowance must be made for the state of the atmosphere, 
colour of object and background ; and too much reliance 
must not be placed on the answers as a means of comparison 
with similar observations made in distant countries) :—1. 
At what distance cau he distinguish the form of a human 
figure moving ? 2. At what distance can he distinguish a 
man on horseback 1 
The existence of Myopia, where suspected, may be 
ascertained by the improvement gained by the use of 
biconcave (short-sighted) spectacles. 
J. ±5. 
Further Notes on Testing Sight . 
Perhaps the simplest and the surest measure of keenness 
of eyesight is the greatest distance at which a square of known 
size that has two of its . sides vertical as in Fig. 1, can be 
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 three such pieces of card 
with squares on them of lj, 1, and f-inch in the side, res¬ 
pectively. An assistant displays and changes them, you stand 
