Belmont chronicle. [volume] (St. Clairsville, Ohio) 1855-1973, 1872-11-07
Professor TyndalI on. Light and
Heat


The second lecture on "Light and
Heat" was delivered at Lowell Insti-
tute last evening by Professor Tyndall.
In opening he stated that these lectures
were not for the learned in scisnce, but
were rather what was called popular,
and that he wished to treat ths subject
in an elementary way, without making
them superficial. As he had explained
and illustrated at his last lecture the
Laws of ofrefraction and reflection ofiight,
he next made use Of the principle Of re-
fraction to study the composition and
properties Of light itself. He projected
upon the screen an image OF the light
Of his lantern after it had been bent by
passing through . prism and showed
that the seven primary coiors wss the
result. The discovery of this fsct was
due to Newton, although Descartes had
studied the rainbow and rightly ex-
planned the cause of its color long be
fore. To the fact that white light is
composite is due the color Of the bodies
about Us. The white filling upon
them penetrstes inso the body. Certain
rays are absorbed, the rest are rejected.
Those which are reflected give its color
to the body. This he showed by sever.
al very beautiful experiments. He
threw white light upon screen and
then placed In the>beam plate Of red
glass when all the colors but the red
disappeared. When, too, a piece ofred
glass was placed in the spectrum, it al
lowed only the red rays to pass through
glass vessel filed with peFmanganatc
of potash, showed when ths white light
Yves passed through tbs coloc Of thi.
beautiful substance. This, the lecturer
explained, was compound color, and
proved 1t By showing that mhe,l u,
spectrum was passed through Z III,
middle ofthe spectrum WIS aasorbet
but that the RED and violet ends wer.
transmitted.
One Of the most striking experiment
ofthe evening consisted in placing Il
the spectrum sticks painted red ant
green. When the red stick was plaee<
in the red of the spectrum it appeared
very red, bnt when it was placed in th,
green rays it became entirely back, be
cause it absorbed all Of the green ray
and there were none to be reflected
He made the experiment very impres
sive by comparing the board when il
the green rays with another which wa
painted black and which it rivalled il
its blackness. While upon this subiec
he spoke of the popular notion tha
blue and yellow when mixed woul,
produce green, and said that this wa
true only of pigments. The reason uh,
they did SO WAS th2t the blue absorbed
all of the red, orange and yellow rays
and that the yellow absorbed all Of tn,
violet, indigo and blue rays, and as on
ly green was left, this was reflected
A very pretty experiment came mex
to show that blue and yellow light
when mixed produedd white. UpeI
the screen appeared a circle OF eaeh col
or, then they were brought together S,
that they oyerIapped, and in tGin over
lapping white Ugnt resulted.
Solar light is very complex, snC
contains rays Of different degrees Of re
frangibility. Owing TO the mpiexii,
of the molecular arrangements OF
body weare able to silt these fNys a1t
70 separate them. The hoDxn system
and brain is very conrpiex, and thus w
are Able TO distinguish them. AS W,
are able to perceive them, our organ
ism must be very complex too, and
seeins as if it were 50 constructed tha
We might enjoy the beauty which re
suits from this complex structure O
light. The eoloIs OF the different oodie
were then shown By placing them OF
one of the carbon points OF Ais electrt
light. Several Of the metals were plac
ed there, and at the temperature OF t{lt
points they were converted into Vaoo
and the vapor burned. ThaIiiuul IA
50 treated, and then It's light was T,,,ss
ed through prism, and single brish
green line appeared upon the screen
This metal was discovered by this yer
means, as no other giveS a green line II
tie same position. Silver ana zin
were also burned, and tho spectrum q
silver and thaliium was projected At sl
same time time, to show that the line
of each occupied different positions, an,
.kfhat il we examine an unknown syh
subsiance in this way we can Fecogniz
first by the color OF its lines and the
by their positions. Tie lecturer state.
{ that to Bunsen and Kirchoif this rueth
cd of analysis was due. In passing I
the explanation of the dark lines OF III
solar spectrum he alluded to fhe lac
that good absorbers of heat were aIs