The Cincinnati daily star. [volume] ([Cincinnati, Ohio]) 1875-1880, 1880-01-10
Light Vibrations,

| Llgnt VlDfatlOnss
Edinburgh Review.l
The sun is, in round numbers, 93,000,-
900 miles from the earth. But the vibra-
tions of light pass across the vast chasm
that lies between the sun and the earth
in 81 minutes or in 495 seconds of time.
In order, however, that they may accom-
plish the long journey in such time,
they must travel with a speed of nearly
1S8,000 miles in a second, or, in other
words, with velocity 100000 times
greater than that with which the vibra-
tions of sound are propagated through
the air. The discovery Of the rate of the
propagation of light was made in very
ingenious and remarkable way by the
Danish astronomer Roemer just two CEN
turies ago.
He was at that time residing at Paris,
and engaged in observing the movements
of the satellites Of Jupiter and, while
doing so, he happened to notice that the
return of the first satellite into the shad-
ow of the planet took place after per-
ceptibly longer interval with each sue
cessive recurrence. After one hundred
returns, the satellite was Is minutes be-
hind what should, to appearance, have
been the proper instant for its plunge
into the shadow. While rejecting upon
the possible cause of this retardation and
irregularity, it occurred to Roemer tina
during the entire period of this observed,
retardation, the planet itself had been
getting further and further away from
the earth as it swept ON its vast orbit,
and that, if the indication of its position
and behavior had to be conveyed to the
earth BY an agent which required time
for its progress, that agent would obvi-
ously need more time for the performance
of its passage when the planet was far
away than when it was near.
Subsequent calculations of more re-
fined and exhaustive character estab-
lished the fact that the eclipse of the
satellite occurred 168 minutes later, when
the earth was on the opposite side Of the
sun to the planet than when it was be-
tween the sun and the planet; or, in
other words, that the vibrations of light
required 164 minutes to make their way
across the entire breadth of the earth's
orbit, or 81 minutes to traverse the half
of that breadth, which is the same thing
as the distance of the sun from the earth.
The vibrations of light, which make their
presence felt by striking upon the nerve
structures Of the eye, are as marvellous
in the matter of size as they are in the
matter of speed. A soap-bubble can be
blown 80 thin that the film is not more
than the l-l56,OO0 part Of an inch in
thickness.
Experiment with film of this char
acter has shown that three or four such,
placed together, would give depth enough
for single vibration Of light. The Ger
man optician, Nobert, by the exertion of
almost inconceivable skill, rules lines
upon glass, of which as many as 112, 900
lie within the span of an inch. Such
lines, again, have been experimentally
shown to be little further apart than
the length of luminous vibration. The
shortest vibrations of light include at
least two such lines in their excursion or
amplitude. The finest light-vibrations
which have been measured are not more
than the 1-57 900 part of an inch in length.
The line which follows here, -, repre-
sents the length of such vibration mag
nifed 10000 times. But if there are 81, :
900 vibrations of light in an inch, how
many must there be in the $4,000, 900
miles which intervene between the earth
and the sun? Fifty-seven thousand in
an inch implies nearly 3,7OO,00O,OOO
in mile, or, in round numbers,
679, 100000 ,0O0,0 in $4,000 miles.
As light travels $4,000 miles in SEC
ond, therefore 679, 900, ,0OO, 900, 900 of vi.
brations must pass any fixed point in the
route every second. or what comes to the
same thing, must strike each second upon
the eye at the end of the journey to call
up in it the sensation of vision. These
numbers, as a matter of fact, far trans
cend mans powers Of exact estimation.
Millions of millions are quantities that
the human mind is entirely incompetent
to grasp in any definite sense; and this
difficulty is materially enhanced when,
as in this case, the millions of millions
have to be conceived as succeeding each
other in the brief interval which is con-
cerned in the single beat of a seconds
pendulum. Nevertheless, it is substan-
TALLY with such quantities that physical
science has, of necessity, to deal when it
undertakes to investigate the character
of light. When beam of clear sun.
shine flashes upon the human eye, shocks,
as frequent and as minute as those
which have been described, strike upon
the nerve-structure of the organ.
Pope Leo XIII recently received the
Baron dAnethan, the Belgian Minister,
at the Vatican, and spoke most frankly
to him On the necessity of bishops and
priests submitting tn the laws of the