( i50 ) 



'J. ci-ossijiii,' of the Nichols 



2. shorter (iiiie of ex[iositioii 



3. jiari-()\\ oi'ilice 



tlic stimulus which otherwise would have amounted to 0.03 ergs per 

 second and ])er square centini. was still considerably enfeebled. 



The Nichols were coin|>letely crossed at 28° 12' of the scale. 

 Hence full light was oblaiueil at 118° 12'. In this position, which is 

 most favourable foi' the Iransniission of light, something is lost on 

 and in the Nichols as well as on and in the media of the eye, but 

 we shall neglect this amount, since it is small compared with the 

 uncertainty of the coefKicienl (»f absorption of the retinal purple, which 

 we will take into account j)resently, and of the distui-biug iiilliieiice 

 of adaptation, ^vhich cannot be entirely eliminated. 



When the instantaneous shutter is moving and gi\es a Hash evei'y 

 0.06 sec. one of the Nichols is slowly tni'ued. The sharp image of the 

 flame disappears and instead of it we see a dot-shaped glimmer, which 

 at last seems to move a little upward. A minimum glimmer 1 found 

 lüitJiont prrv'wiis adaptation to tin' dark 



coming from the right at 3(5°. (>' of the scale 

 coming from the left at %f „ ,, ,, 

 which means a i-olation of tho Nichols of 82°. (V and 81°. 48' oi- a 

 mean I'otation of 81 .57' reckoned from the position foi- full light. 



On account of the crossing of the Nichols we may assume that 

 the intensity in the ratio of cos'. 81°. 57' to cos\0° or as 0.0196 to J . 



liesides the time of exposition was oidy 0.6 milli-secoiids e\ery time. 



Finally the artificial pupil had a surface of no more than 0.0314 cur. 



l>v all these circumstances the original (piantity of energy of0.03 

 ergs, contained in the rays that can be absorbed by the rods, has 

 been reduced to 



0.0196 X <>,<><><>6 X 0.0314 X <><>'^ ("1',^'^ = 1-1^ J<^~' ('I'g'^- 



From the measurements of absorption by A. KciNio it follows that 

 ^'5„ of the light of these rays is retained in the retinal purple and 

 since only the really absorbed light must be taken into acc(Hiut for 

 the stimulation, this amount is still further reduced to 



0.02 X l.l-K)"' (^I'g-s = 2.2X ^<>^'" ^t'g^- 

 In a second series of experiments with a time of exposition of 

 0,00062 sec. repeated every 0.64 sec, and an angle of the Nichols 

 of H4'42' from the position of full light, I found 



0,00854 X^^-^^^^^^^^^X^^'^l-AX^^^^S ergs = 4.9 x lO'-' ergs. 

 And \/5„ part of this is again 



