280 ELEMENTARY PHYSIOLOGY. [XXVII. 



the others. The direction of the line most 

 distinctly seen represents the meridian of least 

 convexity of the cornea. Approach gradually 

 nearer the star and note whether the other lines 

 become all visible at once or in succession. 

 Repeat this first with one and then with the 

 other eye closed ; the astigmatism may be different 

 in the two eyes. 



Then holding the star at a distance a little 

 greater than the near limit of accommodation, 

 fix the centre of the star with one eye, keeping 

 the other closed, and bring the star gradually 

 nearer; the lines will probably not all become 

 dim at the same moment ; the line which 

 remains distinct longest will be the meridian 

 of greatest curvature of the cornea; this is 

 usually at right angles to that of least curvature, 

 so that the line last seen with near accommoda- 

 tion will probably be at right angles to that first 

 seen with far accommodation. 

 Instead of the star a number of parallel hori- 

 zontal and parallel vertical lines may be drawn. 



Or, 



Fix a needle vertically on a board. Looking at 

 the needle with one eye, accommodate the 

 eye exactly for it. Then hold another needle 

 horizontally before the first, and move it back- 

 wards and forwards until both needles are seen 

 distinctly at the same time. This will be found 

 to be the case when the needles are at some 

 distance apart. 



