169 
The corresponding method by which the limit value is reached 
through a slow inerease of the velocity of intermission, furnishes 
especially a stable value at a continuous and regular approach of 
the limit value. The average variations, when this method was 
applied, were in our experiments less than one period (the duration 
of one light-stimulus +’ an equally long absolute dark pause) per 
second. 
(1 draw attention to the fact, that these results, forming a me- 
thodical foundation, are in a certain contradiction to the usual 
indication of application which are spread in the practice of hetero- 
chromal flickerphotometry.) | 
The constancy of the determinations obtained with our method 
renders it possible, that one single determination is sufficient to 
characterise the momentary condition of the visual apparatus. 
The single determinations succeeding one another can consequently 
serve to construe an illustration of the variations of this condition 
during the time of the determinations. 
When applying other psychophysical methods I have found however, 
that the limit values in the same objective circumstances, in the same 
series of experiments are, at great variance with each other. When 
comparing different psychophysical methods I have further discovered, 
that the limit values found do not only vary according to the 
methods applied, but that the deviation becomes the greater as the 
intensity of the flickering light increases. This proves consequently 
that the difference of the psychophysical methods is not only connected 
with a difference of subjective factors, but also with a prepon- 
derating modification of objective physiological conditions. 
The difference in the results of the few authors who have experi- 
mented with quite different methods, is consequently to be explained 
in the first place by the influence of these different physiological 
circumstances. With all succeeding experiments [| have therefore 
always applied the same method, which may be called: the method 
of the uninterrupted, regular increase of the velocity of intermission 
till an optical impression that does not change any more is reached. 
By applying this method, 1 lave tried inter alia to solve the 
question whether the adaptation of light can be regarded as a state 
of relative fatigue. 
For this purpose two series of limit values are compared: one | 
consisting of determinations that were noted after a good adaptation 
of light (15 min. in the sun), the second series, those which were 
noted after a fatigue of the eye. 
It appeared that the state of the visual organ adapted to the 
