The sun. [volume] (New York [N.Y.]) 1833-1916, 1879-06-29

their cut ends are presented to the light reflect
ing the least possible proportion from the sur.
face. while allowing II to penetrate deeply into
the substance Of the fabric.
The magical tints resulting from the polarIza.
ton OF light are never seen In our world except
with the aid OF optical apparatus, but some OF
the most exquisite effects with which we are
familiar spring from a phenomenon OF some-
what similar naturc-the interference OF light.
In this case the effect is produced by light shin
ing upon very thin layers OF any substance. and
comes from the mutual Interference and con-
sequent alteration OF the waves OF light reflected
from the thin films. Where two waves Of ex-
aetly the snme length. but going In opposite
directions. como in collision. they neutralize
each other. and darkness IL tho result; where
waves OF different lengths. and going I'm differ
ent directions meet. tho result is wave differ
ent from either, and the character OF which
| vnries with the force and relative direction Of
the two original fluctuations. The result, OF
course. depends greatly on the angle at which
the reflection takes place and on this account
every change In the position OF the object or the
eye alters tho coors seen by the spectator. To
this cause are owing the shifting hues OF the
peacocks feather aud the humming birds
breast from this come the changing tints which
enchant children in soap bubbles. the brilliant
metallic coors OF insects. and the iridcscent hues
OF shells.
The phenomena OF huorescence, although not
often mot with. are still more curious. II has
been found that some substances have the
property OF retarding the rays Of light which
pass through them. and altering their color by
actually changing their rate OF vibration. One
OF the best examples OF this is to be found in
uranium glass. II a ray OF violet light be di.
rected upon piece Of this glass in dnrkened
room. the glass Immediately CLOVIS with soft
green radiance. the consequence Of n change
effected by II In the length OF the ETHEREAL yibra-
ton. number OF liquids have the same prop
erty and the colors produced by phos pho
rescence often closely resemble those OF fuo-
rescence.
The dispersion OF colors. such as takes place
when beam OF white light falls upon a prism.
and Ia by II separated into the brilliant series
Its constituent tints, although only recognized
by us In the rainbow and some few other rare
occurrences. IL another method by which the
myriad combinations OF color are varied
When We have studied all these phenomena
which. constantly interactlng upon each other
give birth to the changing hues Of the external
world. we find. on turning our attention in
ward. almost as widea field opened for investi-
cation. Our apprehensions OF color are as de-
pendent upon the peculiarities OF our own
structure rs on tho nature OF the original caase.
In the first place. II needs only an abnormal con-
dition OF some tiny part OF the eyeball or the
optic nerve which Communicates between IL
and the brain, to shut us on forever from all
knowledge OF the kind. and there are countless
gradaiions OF imperfection before We reach
that exquisite susceptibility to tho most delicate
variations OF tint which Is the blessing OF only a
gifted few. Absolute color blindness, TO
ono or more colors. in eyes other
wise healthy. is much more common
than might be supposed. In England IT was
found that about one man in every eighteen
was afflicted with 1t. Curious to say. II Is def
cheney so raro In the female sex that compare
lively fewtnstances have been recorded of il,
fact which we notice that Prof. Rood is disposed
to attribute TO tho occupations OF women. which
frequently demand great regard TO color aud
TO the attention which they pay to this point in
dress. Inability TO see the red RAYS is the most
common form OF color blindness. rarer class
oil cases Is that OF persons blind 10 the green
rays OF light This latter condition has been
sometimes temporarily produced by a nervous
shock. Whether permanent color blindness to |
the violet rays ever exists has not vet been de-
termlned. but II can at any rate be superlnduced
Tor time by dose OF the drug santonin.
Tho optic nerve can DO 30 irritated by cleo |
trlcity that the experimenter although en- |
vcloped In utter darkness has the sensation Of |
perceiving brilliant colors. Ritter maintained |
that the current from n strong voltaic battery |
produced the sensation OF bright blue or bright |
green. according as II travelled from the fore |
head to the hand, or from the hand TO the fore |
mead. Hemholtz who repeated tho same ex- |
pertinent, was conscious only Of an indiscrimi- |
nate rush Of colors.
Leaving the consideration OF such denciant
or artificial perceptions of eolor. We and that
Inc essential structure, even OF perfectly |
healthy eye. gives rise TO many notifications of
the colors which actually exist in nature I'M
upon the retina OF the eye have n
definite amount OF durability; they do not in
stantly disappear with the disappearance of the
object which hes given rise to them and in this
way, MS our vision roves rapidly from one OBJ
lect to another there is a certain mingline of
The different Impressions which have been
made upon It.. Again. the nerves OF the eve are
liable to WEAKNESS from prolonged exertion.
and after We have gazed for some time at any
Unit particularly ono OF great intensity. il no
longer produces upon us the same effect
as before, and the whole balance Of our ap-
probation OF colors is temporarily disturbed.
The laws Of contrast. Of the intervals and grada-
lions OF color in painting. take their rise from
mis- fact Our perception OF colors is also. more
frequently than we would imagine affected by
our memory. Knowing an object to be of n Ger.
-aln hue, we fancy We still see il OF the same
Tint although causes OF which we are uncon-
sclous may have interviewed to alter il. There
Is also difference in the relative degree of
susceptibility OF the nervous hbris OF the
retina, according to the amount of illumination
10 which they are subjected. In very bright
light the red nerve is more powerfully affect
ed. thus moving the whole scale of color
slightly in tho direction OF red. the practical
effect OF which is to produce a general yellow
lsh tint; while in waning light the violet nerve
acts more powerfully the result being to cause
generally blush effect. For this reason, in
moonlight scenes, most Of the tints which we
perceive tend toward blush and yiolet.blue
grays. Lingering In picture gallery ut twi-
leht' the greater activity Of the violet nerve
often gives the paintings an entirely unnatural
aspect by destroying tho balance Of color.
Prof. Rood speaks especially Of tho theory
often decidedly promulgated by musicians. AZ
% q correspondence between musical harmony