54 BULLETIN OF THE 



and grouped in the ordinary manner of spots upon playing cards. 

 The recruit would be required to distinguish readily the number 

 of spots upon each card at the distance of twenty yards. By 

 rule of simple proportion this would be equivalent to the recog- 

 nition of a target three feet square at the distance of six hundred 

 yards. The second part of the apparatus consisted of an instru- 

 ment resembling an optometer, having a graduated beam twelve 

 inches in length, carrying a slide capable of being clamped at 

 any part of the length. In the holder is the mounting for lenses, 

 two of which are provided, one of ten inches the other of four 

 inches solar focus. For measuring myopia and hypermetropia a 

 small card bearing a printed sentence in small type is placed in 

 the slide which is first clamped at ten inches from the lens. At 

 this distance the normal eye should be able to read the printed 

 sentence through the 10" lens, and have its accommodation re- 

 laxed. By moving the slide nearer to the eye the amount of 

 myopia can be judged. By substituting the 4" lens and moving 

 the slide away from the eye beyond the four inch mark, the amount 

 of hypermetropia can be judged. To ascertain the extent of as- 

 tigmatism, there is substituted in place of the printed sentence a 

 small card dial having two pairs of parallel lines crossing each 

 other at right angles. The dial can be rotated in a vertical plane. 

 Astigmatism, whenever it occurs, arises from the fact that the 

 crystalline lens of the eye is not isotropic — different meridians 

 having different curvatures. If the disc be placed at a distance 

 from the eyes at which it would be foeussed by the meridian of 

 maximum curvature, and the dial turned so that one pair of lines 

 is parallel to the plane of that meridian, only one pair of lines 

 will be visible to the ordinary astigmatic eye. If the dial be 

 rotated slowly this pair of lines will become indistinct and gradu- 

 ally disappear. The angle through which the dial is rotated 

 before the disappearance will vary inversely with the degree of 

 astigmatism, and thus the amount of rotation becomes a measure 

 of the degree of astigmatism. This device also indicates the 

 positions of the meridians of maximum and minimum curvature 

 of the crystalline lens in the astigmatic eye. 



For testing color-blindness. Dr. Woodward exhibited skeins of 

 colored worsted of all the principal colors and of many tones. 

 From a confused pile the recruits are required to sort out the 

 colors into three groups — red, green, and violet. In case of 



