EFFECTS OF RADIANT ENERGY ON THE EYE. 



777 



by a second prism placed at right angles to the first prism and parallel 

 with the first spectrum. The second spectrum seen through the 

 second prism showed at once that the fluorescent light was made up 

 of rays of different length. Of these the greater portion were green 

 waves, a less portion of blue waves, while a considerable amount of red 

 was also present. In the light of these findings arid after a further 

 study a few months later the following tabulation of the eflfect of light 

 waA^es on the eye was prepared : 



Visible light 

 red to green blue to violet 



I II 



7G0mm-490mm 490mm-400mm 



Invisible ultra violet light 



III 

 400/x/i-375MAt 



IV 



375mm-320mm 



V 



These rays 

 proceed un- 

 changed to 

 the retina 

 and are 

 visible. 



A small part in- 

 creasing with 

 age is by the 

 lens absorbed, 

 and is concerned 

 in its fluores- 

 cence. Another 

 part fluoresces 

 the retina and 

 the rest is seen 

 by the retina as 

 blue and violet. 



A part fluoresces 

 the lens. A part 

 fluoresces the re- 

 tina. A part pro- 

 ceeds unchanged to 

 the light sensitive 

 retina. Whether 

 the appearance of 

 the lavender-gray 

 is due to a direct 

 stimulation or by 

 intermediation of 

 fluorescence is un- 

 kno\\Ti. 



Take little part 

 in fluorescing 

 the lens. Are 

 intensely ab- 

 sorbed by the 

 lens, reaching 

 the retina only 

 in young eyes 

 much weakened. 



Do not 

 penetrate 

 through 

 the cornea 

 but pro- 

 duce outer 

 eye 

 trouble. 



Hallauer ^^^ in 1909 spectro photographically measured the absorp- 

 ti\e power of over 100 fresh human lenses and found it to depend 

 mostly on individual differences of thickness, color and consistency. 

 For young lenses, while most of the rays were absorbed at about 400 nfx, 

 a certain number of more or less weakened rays between 330 nfx and 

 315 ^i/x were able to pass throvigh. The effect of severe or chronic 

 illness in these cases was to increase the amount of all to pass through 

 in the latter region. Also in advanced age, where the absorption lay 

 usually between 400 /x/z and 420 fxii, the effect of severe reducing 

 diseases was to reduce the absorption power to about 375 ju^. 



Martin ^^^ in 1912 found the absorption power of lens suspended 

 in normal salt solution to begin at 400 /x^t and become complete at 

 350 fxfx. 



