Year: 1872




The Boston Post gives the follow
ing report of Prof. Tyndall's third
lecture Of his course before Lowell
Institute


Without prefacing his lecture with
any general remarks, Professor Tyn-
dali proceeded at once to his expert
ments, beginning with one showing
how ray Of light when striking the
surface of water obliquely was re-
fracted. Thus far in his experiments
the lecturer had been considering
some of the phenomena of light; it
was now proper to inquire what
light really is. Newton supposed
light to consist of elastic particles.
He had worked long at the problem
of gravitation, and he knew that
bodies projected in a straight line
would be detected toward the cen
tre Of the earth, and considering
light as matter, he concluded that
refraction was gravitation, and that
color WAS due to difference in the
size of the light particles, the light
er colors being attracted more to-
ward tAe centre of the earth and the
darker colors less. Tested by eXpe-
riments, Newton's theory would ac-
count for many of the phenomena
of light, and that theory was main
tained by Laplaco in his own time,
and Brewster in ours. In 1918 was
born one of the most distinguished
men England ever produced.


Educated physician, he was too
great a man to be limited by pro
fessional routine. He was a master
of all letters and versed in both an
cient and modern languages. This
maa was DR.. Thomas Young. He
discovered facts in optics which
Newton's theory could not explain.
He detected resemblances between
light and wave motion. With re-
gard to these two men, let me use Il
geometrical figure | have sometimes
used. Let Newton stand erect
in his time, and let Young
stand erect in his Draw u line
from the head Of one man and let it
pass to the head of the other. 1t
will descend from Newton to Young,
for Newton was intellectually the
taller man. But the line will not
be IL steep one. 1t will be what en-
gineerS Call slight gradient. Be
tween these two men place the
greatest man that was born between
their times, and his head would not
touch the line, because if it did he
would be greater than Young, and
there was none greater. If there are
any representatives of the press pro-
sent | wish taem to take warning
from this illustration of the power
of public writer's. This great DR..
Young was quenched for twenty
years by writer in the Edinburgh
Reric,r. His assallant was Henry
Brougham, who atterward became
Lord Chancellor of England.


A series Of experiments were here
introduced to prove that light con-
sists of pulsations, showing, by
means of tuning forks Of different
sizes, that the waves of light that
produced the different colors OF the
spectum correspond to the different
vibrations OF the tuning forks. The
waves of red were long and slow,
while those of orange and violet
were more rapid. Unlike the waves
of sound, however, Young discover
ed that the waves of light were trans
verse and not longitudinal, resemb
ling in their motion the different sec
tions Of a rope when held at bott
ends and shaken. 1t is to the one
which is now generally accepted
Other experiments were then intro
duced, shoaing how light might be
prolonged by tourmaIine, by mir
rors placed at u certain angle will
the light, and by Iceland spar. The
principle of interference in light a.
well as in sound was Illustrated by
sounding two tuning forks, one be
ing little below the pitch Of thu
other. The waves of one will mega
tive the waves of the other, and 81
lence will ensue.