168 
the intermissions) at which the impression of fusion becomes just 
noticeable does not only depend upon the intensity of the inter- 
mitting stimulus (Scuenk, Marse and others), but also upon the 
funetional condition prevailing in the visual organ. SCHATTERNIKOFF 
e.g. has found that the frequency at which the fusion sets in, 
diminishes not only with a stronger intensity of the intermitting 
light, but also with a stronger adaptation of obscurity. 
Some introductory experiments have taught me, that likewise a 
previous strong stimulus of the eye with the strong source of light 
described above diminishes the frequency for the fusion. There is no 
doubt a certain connection between the measure of diminution of the 
limit value (Schwellenwert) and the duration of the penetration of the 
stimulus of fatigue. The limit value for the fusion (i.e. the number 
of interruptions at which it just sets in) can serve as a measure 
of the fatigue prevailing at the moment of the experiment. 
As bowever the results of some authors who occupied themselves 
with the analogous limit values, differ very considerably, I intended 
to find the cause of this fact, and to avoid it in my own experiments. 
In the first place the moments mentioned already in literature 
that can cause the differences in the limit values were carefully 
avoided in a special apparatus. A constant light of a Nernst lamp, 
placed far behind a row of milk-glasses, is periodically interrupted 
by a massive metal dull-black-polished turn-dise with 12 equally 
cut out sectors. Before the dise a white screen was placed with a 
little opening fitting to the sectors. The illumination of the screen 
is always kept constant with the intensity of tbe light of the 
flickering hole.*) Further a maximum exercise of the experimental 
person is reached, and at last the relation is sought, at which the 
judgment of the experimental person is most stable. 
It appeared that the experimental person must not wait during 
the experiment till the impression of an ideal rest within the visual 
field is reached, but must cease at a nearly imperceptible unrest 
within" the optical field, as soon as this impression no longer 
changes with the further augmentation of the velocity of interruption. 
In reality the number of the interruptions per second at which the 
fusion takes place, is not taken into consideration as limit value. 
The most positive limit value corresponds much more with the 
number of interruptions at which only the distinction of the separate 
stimuli is no longer possible. 
1!) The mechanism for the regular modification of the revolving-velocity and 
likewise a number of little cautions for the stability ‘of the exterior conditions | 
describe in an elaborate publication. 
