118 ELEMENTARY PHYSIOLOGY. XXIII. 



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 last seen with 

 near accommodation will probably be at right angles to 

 that first seen with far accommodation. 



Instead of the star a number of parallel horizontal and 

 parallel vertical lines may be drawn. 



Or, 6. 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 backwards and forward* 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. 



More exact results are however obtained by Schemer's 

 method ( 4, 5). 



9. Irradiation. Cut out two patches of exactly the 

 same size, of white and of black paper. 



Place the white on a sheet of black and the black on 

 a sheet of white paper. 



Place them some distance off and adjust the eye so as 

 to throw them a little out of the range of accommodation. 



The white patch will appear larger than the black one. 



10. Blind spot. Make a bold mark on a sheet of 

 white paper, place the sheet on the table, and, closing 

 the left eye, fix the axis of vision of the other, by stead- 

 fastly looking at the mark at a distance of about 25 cm. 1 

 Dip a new quill-pen in black ink and place it a little to 



1 Fix a small square (about 5 by 5 mm.) of black paper on the point of 

 a teasing needle. 



