National Republican. (Washington City (D.C.)) 1872-1888, 1872-12-10
PROF. TYNDALL.
HIS FOURTH LECTURE ON LluHT.
Interesting and wonderful Experiments
The R,th,.i,.r, n The Audt,nrc

Interesting and wonderful Experiments
The Bnthuslasm OF the Audience.
The intense cold Of last evening did not pre-.
vent the usual large and brilliant attendance
upon Professor Tyndals lectures at Lincoln
hail. and all who brayed the Alpine blasts, cut.
ting and piercing to the very bones, were amply
repaid. The great teacher and philosopher was
never more happy In his verbal Illustrations and
in the perfection Of his experiments than last
night-in fact, the latter were so nne, owing
mainly to the skill Of Mr.. Cottrlll, that the Pro-
fessor paused moro than once to compliment
Professor Tynda,l made brief hut necessary
review Of the lecture OF Saturday night, and, In
substance, said the mysterious mud called ether
produces fluctuations OF light by transverse
vibratOns,or to and fro across the line Of produC-
ton: Science IL powerless when y attempts TO
! explain how waves Of ether awake these impress
slons. The ohAsm between the physical and
sentient has never been bridged. Science IL all
powerful when dealing with outward and tan.
! fllm on piece OF rough gypsum and Introduce
It between Ncol prsms and show lts effects In
thin plates the colors are observed, and In thick
A piece Of Iceland spar was employed a. a
| polarlZer and Nlcol'a prism ~ an analyEer The
Illustration went on s mo shst When ne S ths
| conceded, the light passing through both was
| received upon the screen; but when the yibra-
sS SsS s6d tSa
! screen became dark. When the screen was dark,
he interposed thick plate Of gypsum, with its
SnaIynS and White g6t reached he scre Sr
! when a thin plate was interposed the screen was
| cOlOred. II the plate was Of uniform thickness
the color would be uniform, and when OF differ
! ent thicknesses, different cOlors appear.
These principles, the Professor SAID lead us
into a new world. II IL one OF the suhlimest re-
are to follow are not simply things 70 excite curl
/ Oslty, but TO enforce and Illustrate principles.
Then followed experiments to show the effect
| the effect Of heat on glass cheated ~ a common
spirit lamp on pOlariZed light. one OF the best
| Instruments to determine the amount Of pressure
| had been Invented by Wertier, Of Paris. When
/ the glass was not pressed figure Of white light
| appeared on the screen; when Il was pressed all
| the cOl0rs Of the spectrum appeared. Aud then
| proof was Afforded that heating plates OF glass
| produced strains and neutral axes, the latter
making black lines on the screen, while the parts
under strain seemed TO be bright. A square Of
! glass with q hole In the centre having a wire
passed through IL was then introduced, and
showed the effect of heating the wire. When
the Nlcols were crossed black cross was pro-
duced, and then various specimens OF unanealed
glass, In which permanent strains had been made
by sudden cooling, were made to throw upon the
screen the most beautiful cOlors and In most
beautiful forms.
But we do not rest here; we take a step be-
yond. The crystals shown exhibit pOaTtEed
light In one plane. Some crystals are so con-
structed a. TO cause the direction OF vibration
TO move In circles. A pendulum was suspended
on the stage, which Professor Tyndan swung In
the ordinary way. II you give II blow at the
though In different direction from the nrst, but
u u In struck blow at right angles to its motion
on the outer limit OF It's swing II will then yihrate
round In q circle. Similar phenomena take place
In rock crystals. When polariEed ray Of mono
chrOmRtic light Ia transmitted through crystal
(or quartz In the direction OF the optic axis, Its
plane Of vibration Ia turned by the crystal. Some
specimens Of crystal turn the plane Of vibration
TO the right and are called rlght-handed crystals,
and some turn II TO the left and are called left
handed crystals. Sir John Herschel connected
this optical difference with the crystalline DIFF
ference.
Then followed splendid experiment, showing
the Complementary cOlOrs from hlGefraCtinR
spar. Two images Of circular hole were passed
through quartz plate. The Complementary
colors produced upon the screen were blue and
yellow. The image was separate. The hole was
made larger, and the images caused to overlap.
White light was produced In the overlapping
part, thus proving that blue and yellow light
make white light And after this sensation
was produced by an explanation Of pigments
that IL, why blue and yellow make green. A
spectrum was thrown upon the screen: Blue
yellow and left the green and blue end Of the
spectrum. yellow liquid was introduced which
cut on the blue end Of the spectrum and left the
duced together, the green only was left on the
spectrum.
further explanation Of the experiments in light.
BY rubbing long glass rod with piece Of wet
flannel sound was produced. At the middle Of
the rod the same state OF compression aud ex-
panslon existed. This was proved by placing
the bar between the pTlsms and fastened In a
vice, and the same musical sounds were pro-
duced. These sounds were simultaneously aC-
companied by flashing OF light on the screen.
SO Blot was given the credit for the discovery by
which he was enabled to show the action Of
sOnorOus bodies on light.
derful experiments In the mAgnetization Of a
beam Of light. No one, he said, can predict