New-York tribune., 1873-03-12
OPTICS AND PAINTINGS.

RETINA.
The eighth lecture of the Art Course at the
Academy OF Design delivered last evening by fro
ogden NJ Rood of Columbia College, aud was continn
aton Of the preyious lecture upon the "Reatons oi
Modern Optics to Painting" 1t illustrated as De-
fore, by many diagrams and experiments.
Al the ouset Prof Rood said that in the last lecture
ne had shown the ncorrectness Of the old theory tha
red yellow and blue were the primary colors Accoru'
ing 70 that theory when blue and yellow were mNeu
the result would be green but there was abundant e
dence that nothing of the kind took place ho
had also given the main points OF IhoiD"'
Younc,s theory that in the retina OF the eye
there were three sets Of nerves, one OF Whicn
was devoted to the sensation OF red light one TO green
and another TO violet light that those three coors were
the true primary colors and that by suitable mlnsne
OF these we were enabled 10 obtain the other uh'S
Several experiments tried to test the correchesso
these two theories. We combined red, yellow ana puo
light upon the SCREEN but the result was not whte ou
strong red tint. Combining red, green and voet We
obtained very excellent white light. wish now 70 eA
plain TO you very simple form by which you can repeat
these experiments for yourselves have now upon tho
screen diagram of method used by Helmholtz IL Is
pane of common window glass, placed erect upon
blackened board. Upon one side we place sheet VI
blue paper which reflects its color upward 10 the eye
On the other side IS sheet OF yellow paper "non
does not reflect the rays. but SENDS tnein
straight up 10 the eye IN tldt way VIC kSb
This apparatus is rendered still more valuable Dy tne
facility with which the intensity Of the two beams can
be moderated by the simple operation OF moving thema
little further apart bringing them little nearer
have shown this diagram thus early because 1t is quite
useful in some other matters that have TO show THIS
evening. -
The apparatus which have here is nothing but
board with different coors upon it, BY combining yell
low and blue bring them into suitable juxtapositon to
make white light Any two cOOrs which thus, without the
aid of any other coors produce white are called compile
mentary colors. On this diagram you see the word
red" and written opposite are the words "bluish
green" BY combining red and blush green we obtain
white The same result Is obtained with combination
of orange and greenish blue; OF yellow and uramarine
of grass-geen and purple Of emerald green and ear
mine Many OF you have heard that the Complementary
color OF red green but such is not found to be the act
II is blush green The Complementary color OF grass
green Is purple combination OF blne and red II Is the
usual idea that with diagram of this sort ii Is exceed
incy easy find the complementary colOrs, but on the
other hand ii requires long practice 1t is much easier
10 obtain them by the aid of poarzed light The expert
ments which will make in that manner will not cor
respond perfectly account OF the influence of the yell
low gasght, which mngles with the colors upon the
screen and alters them somewhat. Here we have red
light and blush green and where they overlap Is ev
dent that white light is the result. Different com
binaOng, each comprising only lNO CoIoIs' "tio NOH
thrown upon the SCREEN showing that the result in each
case was the production Of white lght) You will notice
that one tint is brighter than the other, though some
times OF equal brightness With any one color we
may have many different complementary coors Useful
as the TINS Of poarZed light in studying these com
Elementary colors, find that the tints are always
prsmac they too pure too much Ike the spectrum
tnts Suppose have kind OF blue or gray OF which
we want to find the Complementary colors Bv employ,
ing the apparatus OF Hemhotz Is only necessary 10
color piece of paper with the TINT OF Thch we Ieste
the comuement and then color another piece with the
supposed complement Then. by this series or expert
ments you very get the actual Complementary
color. ---,,-.- 4. x,o,,..,,
theory The idea is this that only those c0iors arc COM
Elementary the Joint action OF which sets ali the nerves
all the three sets of nerves. into equal action TAKE tne
case OF and emerald green The green sets the
nerves green into action the carmine sets into OuOh
the nerves OF red and violet so that by these Two coO
all the three sets Of nerves are equal action lake
the yellow and blue The yellow sets into motion tue req
and green nerves. while the blue puts into action the
green and violet. The same explanation would noni
with regard to the other portions oi the diagram upon
'"' THE EFFECTS OF NOTION
This persistence Of VISION this duration OF the impress
sion upon the retina. has quite an important bearing
upon some matters that wish to speak Of presently
and in the mean time will merely state that the artist
in painting objects which In notion always gives
the substance general appearance OF good many dis
tnct Impressions they being fused together in this way
Now take (this matter in connection with the duration
give a rational explanation OF the phenomena OF con-
trast. which all Important IN the appearances
presented 10 nature and in the paintings which are
produced by artists me ehect %hleh helgnoQQTlns Qs
masses light and SHADE have on each other was Illus
trated 10y throwing color upon white or gray ground
ioncng AT the color for instant the eye 10
certain extent sensitive to that particular color and
oGT was made TO reyove and slowly 10 cease turning
the white gray ground appeared to be ngcd with the
me lecturer here spoke Of the direct perception OF
distance which the human eyes possessed although the
distant objects might be so disposed OF TO appear OF
the same color and shade, and called attention 20 he
wonderful way in which photographs confuse distances,
and said that the total lack of power In the painter to
emnloy real distances in his views seemed a iustfca-
ton from scientific point OF view, OF the alterations
In color and in hight and shade which otherwise might
he questionable although lie thought them unwise VINO
despised such alterations from purely scientific point
OF view Some Of the features OF linear perspective were
then explained by illustration and subsequently the i'm
measurable superiority OF Natures palette that of
the painter. nstaDced by the illumination found In ma
ture the wide difference between the actual sky and It's
representation canvas lt was ascerained in an eX-
pertinent, comparing moderately bright sky with
painting Of IT, that the former was just two hundred
times brighter than the white paper, that from the
200 that is 400 grades while the painter has only 81
AT his command with which 10 represent those different
was mentioned almost startllng experiment. for
the coors are brilliantly Illuminated. and the sky If you
are sitting in the daylight, Is immeasurably brighter
than thar OF an ordinary painting on canvas
Upon retiring a suitable distance very charming
appeas 10 be disk of white light but by examining il
closely you win that It ~ entirely composed Of red
ereen and yellow particles. There Otner processes
employed by nature, which are very little used Dy
artists To call them turbd media implies much; 10
call them troubled media implies TOO little. The idea y
this that when fund medium like water is filed with
small fne particles, the shorter waves OF light are re-
hected.
prof Rood demonstrated this fact ny minglng mastc
yarnsh with water, producing blush rejection, ana
stated the PARTICLES OF suspended matter were sOj
small as hardly To be dscerned with the MICROSCOPIC
After speaking OF the blue color OF the sky and OF ais
tant mountains, which due 10 the Interference
OF light and remaring incidentally for the benefit OF
the ladies that the most beautiful blue the world
aid not contain single particle Of blue pigment. but the
simply the effect OF troubled media spread over
dark ground the lecturer concluded with the sugges-
,ion that we allow the painter 60 use all and means
which his nature instinct shall lead him % adopt,
promising him our thanks and praise for filing our
IL. Iun... a.I MI ILLan