41 
of drawing conclusions from these data is indicated in the 
paragraph on Statistics, p. 226. They afford a complete and 
approximately correct picture of the distribution of the 
qualities tested, and not merely general averages. 
No. XVII.—THE SENSES. 
Sight and hearing are generally supposed to be more acute 
in persons belonging to tribes who have long dwelt in open 
countries and led a nomadic or insecure life. Myopia (short 
sight) is thought to be extremely rare among savages, who 
exercise the eye very little on minute objects, while their 
smell is more acute than fastidious. Exact data on these 
subjects are desirable. 
(a.) Sight. 
Attention should be paid to (1) Acuity of distant vision, 
and (2) Colour-sense. 
(1) Visual acuity is best estimated by using Snellen’s 
Test Types. The special advantage of this method is that 
it permits us readily to compare the vision of different 
individuals, as the acuity in each case is expressed by a 
definite fraction (see below). 
For illiterate persons, modifications of the method are 
employed, the best of which is probably that known as the 
E type (see Plate VI). For our purposes this method may 
be shortly described as follows :— 
A test-card shows the form of the letter E in different 
positions—E : " 9 , LU, HI- The person under examination is 
given a large E, which is usually shaped out of thin metal, 
and provided with a handle : this he takes in his hand, and 
he is instructed to put this E in the same positions as thqse 
represented on the test-card. The size of the E on the 
different lines of the card gets progressively smaller from 
above downwards ; and the number of metres at which 
each line ought to be recognised by a person with average 
vision, is indicated on the card by small figures corre- 
