9
Discrimination of shades of gray for different intervals
of time.
iato the 120 sec. intervals, and found that the recognition of one of
two shades of gray for 120 seconds with distraction was as accurate
as for 30 sec. without distraction. Accordingly, he argues as the
writer has urged in case of clangs (Amer. Joum. Psych XII, 69)
that such judgments cannot be based on memory images of the same
kind as the stimuli.
Two other factors remain to be considered in this connection —
the formation of free judgments and the results arising from ob¬
jectively like stimuli. These topics will come up for discussion m
the second part of this paper.
Experiments of the second part.
In the spring and summer of 1901 the above experiments were
repeated at Stanford University to see if the results of the Würz¬
burg experiments would be confirmed by other reagents and under
better experimental conditions. The Marbe color-mixer was mounted
on a weighted box insulated from the experiment table by spongy
rubber. The mixer was driven by a smoothly running Edison motor
also mounted on an insulated box, whilst the experiment table was
separated from the floor by several folds of cloth. In this way with
the bearings of the apparatus carefully oiled and adjusted there was
no metallic rattle or resonance from table or floor perceptible. The
disc of the color-mixer was about 8 feet distant from broad double
windows covered, as in the previous experiment, with several layers
of white muslin. Experiments were carried on in a room built for
the purpose of black paper and open on the side toward the window.
The exposure curtain was about 75 cm wide and mounted on a spring
roller. Back of the curtain, black cotton-flannel was so hung that
nothing save the disc and its black back-ground were visible when
the curtain was raised. The conditions as regards colorless light
were so good that the reagents complained of colored after-images
arising from a tinge of color in the paper of the note books, so that
it became necessary to cover the note-book pages with black card¬
board through which slits were cut for making notes. In addition
the reagents rested their eyes on the note-books as little a possible.
The reagents were Alvin Borgquist (Bt), a mature student with