The mirror. (Stillwater, Minn.) 1894-1925, 1904-12-08
SNEsOTA, THURSDAY, DECEMBER g. 1904

position given the series letter ga
tends to arrest the sight before the
end of the line is reached. Hence the
illusion, which is very striking even
when not contributed to by the Ioca
causes last mentioned.
In exhibit five we have, perhaps, one OF
the most deceptive figures, combining
as it does manifold causes of illusions
Measurements made from the inner.
most points of the diminuendo-like
space at the top and base of the figure
show that the trunk, or vertical sec.
tion, of the cross is at least one.
seventh shorter than the horizontal
arms.
A satisfactory solution Of this irresist.
able illusion is more difficult of attain.
ment than has been the case with any
OF those preceding. 1t is quite Ger.
tain that each and the several of the
foregoing explanations apply here
with equal force, and in addition there.
to we have to take into consideration a
new element known as the "error of
expectancy" that is, we naturally ex.
pect to see the arms of a cross shorter
than the height of it, and as result
we rather insist on seeing it that way
even when-as in the present case
the reverse is true. In connection
with this exhibit we may also note that
as heretofore explained, the placing of
the series letter "S" at the apex mate
rally adds to the illusory effect.
Exhibit six shows pair of straight
lines which appear to be decidedly
warped. The four horizontal lines are
exactly parallel and positively straight
appearances to the contrary notwlth-
standing. An explanation is to be
found in the fact that we underesti.
mate the size of cbtuse angles, and
exhibit seven shows the reverse effect
due to our tendency to overestimate
the size of acute angles. A more de-
tailed explanation of the principles
governing these two illusions may be
found on page 1870 of the class book
treating this subject. Under certain
conditions two or more objects of uni
form dimensions may appear to be
very far from being equal. Exhibit
eight shows two figures Identical as to
size and contour; again new principles
confront us and we learn that when
comparing the size of objects we al
most invariably judge them by the
comparative size of adjoining sides.
In the case of the twin figures here
with shown the large side of the one,
designated by the letter ct" is next to
the small side of 20" and, as we invol-
unfairly compare these adjacent sides
the illusion follows.
Illusions of perception are by no
means confined to space and outline;
they are quite as strikingly manifested
where colors are concerned, and, with
out attempting to trace color illusions
thru the various technical channels
we may note, in passing, that white
objects invariably appear to be much
larger than black ones.
In rural districts, remote from scales
stock buyers are oftentimes called
upon to guess at the weight of live.
stock, and am told that it is their
custom to reduce their guess on white
animals and to add to the apparent
size of black ones. And this illusion
is not confined to black and white
Red, orange and yellow objects look
larger than do blue or green ones OF
like dimensions. Another source OF
color illusions is found in the fact that
certain defects in the eye cause certain
colors to look closer than others.
Thus red objects look to be nearer
than green ones, and it is related of one
of the greatest of psychologists that on
one occasion his attention was attract
ed by church window which had a
red disk in green background. The
red appeared to stand out from the
green in so noticeable a manner that
he was not satisfied till, after the ser
vices were over, he went to the window
in question and examined it. The
colors were in the same plane, but
as the red might have stood in projec
tion, the illusion was not counteracted
by his knowledge of the perspective
and he records the result as being al
most irresistible.
While some persons may consider