New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1872-12-20

fts ant
who lived till 1872 and Blot and Brewster Mno n'o" '
Still even az an early period of the existence OF ,ne
Emission Theory one or two great ,b h nieb another
Illustration OF the law that in forming theories tne
scientific imagns1n nHS, If was known long ago
that sound conveyed in waves ana pulses tnto1gn te
AIR and this truth well housed in the mlnd was
Transformed into a tbeoretic conception II was sup.
nosed that light like sound might also DO the prOuuot
Of Ngmnc t wsVss For the waves OF sound
the air Of our atmosphere but the streten OF
bling with the of light so bold as TO snGeR
sr David Brewster ne said to me that his chief ohec
on TO the undulaery theory of light was that ne eOuu
moi be nS Of sSsco with ether in order produce
light This, may say Is very dangerous sroi.hu many
Other persons that they profess to know too much
about the mind OF the Creator
THE BAsIs OF THE UNDULAToRY THEORY
This copcepon Of an ether was advocated by the cele
brated astronomer Huyghens, and by the celebrated
mathematician, Euler They were however opposed
by Newton whose authority al the time bore them down.
Or shah say it was authority merelyi Not quite so
Newtons preponderance In some degree due TO the
fact that though Huyghens and Euler were right IN e
MAN. they did possess sufficient data 10 prove tnen
selves nsn e 10 a San Se Voice Of Nature Speaking
through experiment But the voice of Nature may be an
was the case at the period referred and at such
period by the authority OF Newton all antagonists were
Still this great Emission Theory which held its ground
IN rcsemhieQ those
10 your couDtryman, Emerson, the force OF genius
periodically draws round the operations OF the lnelecI
Om S BEHIND a' In the yer IT'S was borS at veron
in Somesetshre, Of the most remarkaoe men tnat
England ever produced. He educated for the
profession of physician hut was TOO strong 70 De 9eu
down professional routine. lie devoted hlmseI 70
the study of natural philosophy and became in all its
departments master. He was also master Oh let
within his brain and to use the words Of his eptaph,
he first penetrated the obscurlty when had Vaeu lot
ages toe herogyphics OF Egypt" 1t fell to the lot OF
this man to discover facts in optics which Newtons
theory was incompetent 10 explain, ana ms nina
roamed in search OF sufficient theory He had made
himself acquainted with all the phenomena OF wave
motion; with all the phenomena OF sound working r sue
cessiuy in this domain as an original dseoveIer linus
ana re se Between S the phe
banoes did deec and, spurred on by the discovery
he pursued his speculat0ns and his experiments until
he finally succeeded IN placing on iInmOv able basis
the Undulatory Theory OF Light.
THOMAS YOUNG AND HIS OPPONENTS.
rhe founder of this great theory Thomas Young a
name, perhaps unfamiliar to many of you. Permit me-
by kind Of geometrcal construction which once en-
ployed in London give you notion Of the magnitude
of this man. Let Newton stand erect in his age and
Young in his. Draw a straight line from Newton to
This line would slope downward from Newton to Young
Newton certainly the taller man OF the two
stature was excessive. The line would form wha
engineers call gentle gradient from Newton TO Young
born in the interval between both. H'
would not IN nv opinion, reach the line
for if he did he would he taller than Young
and there was, believe. none taller But do not want
You rest on English estimates OF Young; the German
Hcmholtz kindred genius, thus speaks of him " ia:
one OF the most profound minds mat the Wor1 ma
but ne had the misfortune 10 De 100 nuch III
Of his age. he excited the wonder OF ms co
tempOraries, who, however unable TO follow hlm
TO the nights at his daring intellect was accus-
toned 10 soar His most important ideas lay, there
Society until generation gradually and painfully
made the same dseoyGTei ara proved t9e exaetne' Oh
II quite true. Helmholtz says that Young was in
advance OF his age; but something is 70 he added which
llusffat
90 wears this Of genius quenched-hdden from
the apprecatye intellect Of his cOuntrymen-deemed in
fact dreamer through the vigorous audaety OF writer
who had then possession Of the public ear and who in
The Edinburgh RereO poured rdicule upon Young and his
spocuatons To the celebrated Frenchmen Fresnel aud
Araso he first indebted the restitution Of his
rights. they. especially Fresnel. remade indepen-
IDENTIFY HemhOltz says, and vastly extended his dis
since appeared in his true light but these 20 blank years
rushed MN RON the P3nc l9nd when became N turn
Institution, Dayy and aferward with the fame of Fara
day Carlyle refers 10 a remark Of NOvais that mans
seitrut is enormously increased the moment he finds
that others believe in him IL the opposite remark be
trurf 10 b. fact that public disbelief weakens mans
force, there is no calculating the amount OF damage
thco % years Of neglect have done to Youngs pro
ducnvelass rs an lnvestgatOr IL remains 10 be stated
that mis- a,saian was M Henry Brougham' afterward
WAVE UPON WAVE.
Orr hardest WORK is before And have
often had 10 notice that capacity for hard work
depends in great measure in the anteeedent winding
MP Of the VIII and determination, would call upon you
10 grid up your Oins for the abOrs before II
we succeed in climbing the hill which faces tonight,
our future la6ors will be comparatively light In the
earliest writings Of the ancients we ind the notion that
sound conveyed by the air Aristotle gives express
SION TO this notion and the great architect Vlruyius
compares the OF sound 10 waves Of water. But
the rcai mechanism of wave-motiOn was hidden from
the anCents and indeed was not made clear until the
time OF Newton. The central difficulty OF the subject
was 10 distinguish between the motion of the
itself, aud the motion Of the particles which at any
moment constitute the wave
stand upon the seashore and observe the advancing
before they distorted by the friction of the
bottom. Every mas back and front, and If
clearly se.ze TIE Image Oh e MOVING wave YOU viii see
the act Of rising while particle along its back
is in the act Of sinking The particles IN front reach IN
succession the crest OF the and the crest
passed they begin 20 fall They then reach the furrow
Of the and can sink no farther Immedt
atey afterwards they become the front OF the succeed
ing wave, rise again until they reach the crest and
then sink before. Thus, while the waves pass
onward horizontally, the individual particles simply
lifted up and down vertically. Observe sea1Owl, or, II
the waves; You are not carried forward, but simply
rocked up aud down. The propagation OF wave Is the
propagation OF FORM and not the transference Of the
substance winch constitutes tle wave. -, . 4.
The length OF the Is the distance from crest TO
crest while the distance through which the individual
particles Osciate called the amplitude OF the 0scula-
Ton YOu will notice that in this description the partl-
Giles Of water made 70 yDrae across the line OF prop
agatiOn. 49, -
most mpOrtan ant step of ALL You picture two
of proceeding from different origins through the
same When. for example, you throw stone into
still water, the ring-wayes proceeding from the two
centerS OF disturbance ltersect each other now no
matter how numerous these waves may be, the law
holds good that the motion every particle OF the water
s. the algebrdie sum OF all the motions impaired 10 IT,
crest coincide with crest, the is lifted TO double
hight II furrow coincide with crest the motions are 10
opposition, aud their sum Is zero We have then still
water, which shall learn presently corresponds TO
feet. THIS action OF wave upon wave IL teeunlcay
called interference, a term TO be remembered
ANALOGY BETWEEN SOUND AND LIGHT.
Thomas Youngs fundamental discovery in optics was
that the principle OF Interference applied TO light Long
prior 20 his time an Italian philosopher Grmadi, had
49,