Evening star. [volume] (Washington, D.C.) 1854-1972, 1890-08-02


I~ $4,000 miles q second means2 Can
your imagination. able though il may
- be, grasp the idea, without confusion
S Hardly The human mind, keen and
| perceptive, breaks from control at the conce D.
non OF 90 Tremendous . velocity. But the uni
verse mas Messenger 90 speedy that he could
almost outfoot thought ITSELF That mes-
senser fs light and he is so swirl and subtle
| that scientists adore him as tho king tale
bearer Of the universe.
Let us try and conceive what il means when
We compare the velocity of light with those
veiocities We know something OF and are
s s 70 deal with Our limited express
trains travel With an average speed OF 40 miles
per hour. Suppose that Imaginary line
| around the earth-the equator-were repre-
sented by steel railroad and that we start
one OF our Limited express" trains from q
| point giving il . speed of 20 miles an hour
with right Of way around the circumference
OF our globe, free Of stops, for any purpose
whatever. In 600 hours IL should be at the
starting point, having made its journey
OF 1900 miles in that period. or Is DAYS.
Suppose. now, we could give to our train the
velocity of light 1t would make the same
Journey in the ninetieth part OF q second!
Rather rapid travel, is il not? What one Of
| us can divide a second of time into ninety
parts and realize one Of those minute
divisions mentally?
| AROUND THE EARTH WITH THE SPEED OF LIGHT
If We could send a messenger from the earth
to the sun, and could impart to him a velocity
equaling that of light, he would make the
journey in about eight minutes, and that
| means that he would travel about 80 coo, 900
| miles in that brief eight minutes. But il he
made his trip on our limited express going 40
miles an hour he would require something like
two hundred and sixty years to make his
| journey.
1t is easily seen. therefore, that scientists in
dealing with the velocity of light fool with a
problem OF no mean proportions, and it appears
truly wonderful to the unscientifc how it is
| at all possible to measure such enormous
velocities. Notwithstanding the extreme deli
| cacy required IN the operations used TO
determine the velocity of light. the various
| efforts have ended in fairly accordant results
| the accepted value 1S6 32S miles per second)
being that obtained by our own Professor
Newcomb from a series Of delicate observa-
| tons at Washington city in the years 1850 80.
Ii may be interesting even to the unscientifc,
TO know something Of the first discovery that
| light transmission was not absolutely instanta-
\ neous. In the year 1875 CLAUS Romer observed
| that the eclpses Of Jupiter's satellites always
occurred later, by some minutes. when the
earth was on the far side of her orbit, with
| respect to Jupiter. Later Delambre undertook
the determination Of this problem, with a
resulting value Of 493 seconds for the passage
| OF light over one-half the distance across the
earth's orbit. Glasenapp, a Russian astrono.
mer, afterward raised this amount TO sol
seconds-about eight minutes.
| DISTANCE OF THE STARS.
In the measurement OF the distance OF some
OF the nearer fixed stars by means OF their annual
parallax the results, if expressed in miles-our
favorite unit of distance-are SO enormous that
| the mind does not conceive with clearness the
| immensely of that distance Convenience
| therefore, prompted the adoption of the term
| light unit" This is expressed by the period,
| in years, required for light to pass from the
| star to the earth. The nearest known fixed
| star Is Alpha Centauri, the brightest star in
the constellation Centaur. Suppose this star
| were blotted out of existence January l. 1890
1t would still be visible to us on January L.
| 1894 and would not cease to sparkle until May
OF that year. Its distance is four and one
| third, as measured by the light unit, or in
| other words il takes light travelling 1876. 600
| miles a second four and one-third years TO
travel from that star to the earth, and that
| means distance in miles OF over Is 600 600 CO.,
WHAT LIGHT rs.
| II would be Q trihe unsafe to declare lust
what light 10. We realize it in all sorts of con-
ditions, tone or shade and intensity 1t can
| reasonably be stated that light and sound are
| identical In that both are transmitted in waves
| TO our senses-light, OF course far exceeding
sound in velocity of transmission. We also
know OF light that the waves of light differ in
length, for il a ray Of it be sent through a
prism of glass, which has the property of bend
ing it away from its course we find it displayed
as strip Of colors each particular portion
representing different wave lengths
Place slit before that prism of glass and we
have simple spectroscope or light ana
lyzer." For the purpose Of scientific researches
OF great delicacy the spectroscope is usually
made with train" Of these glass prisms The
little three-cornered piece Of glass, then has
become the greatest servant of science Let
us go little out Of the way and see what can
be done with ray Of sunlight and the glass
prism.
We admit this messenger from the sun
through the little slit of our light analyzer Ii
passes through our glass prism without hin
drance to speak Of but what a change! That
ray OF light Is no longer the ray that crowded
through the slit OF the instrument. What we
now see is beautiful strip of variegated light
| commencing with q deep red, running into
| orange, yellow, green, blue and ending in
| violet Our prism has separated our ray of
| light into its component colors Then white
| light Is more than white light. 1t il really
| combination of lights of these various colors
| But il we notice carefully we see more than
| this. We see this band of colors, which scien-
fists call the spectrum" crossed by dark
| lines, vertical to the length of this band of
| color. and varying in length and thickness.
| What do these dark lines, which are really va
| cant spaces in that band, mean? This: That
those dark lines are, in reality. the images of
| that little slit which fail to paint themselves
| All tubt pduu VI cOiOfs DtCduse something mas
| stepped in and cut out that particular part of
| tine white light which ought to fall in the
| spectrum, where the dark line occurs. Science
has discovered that these lines on vacant
spaces mean that the vapors of certain SUBJ
| stances have produced these absorption lines
for such name is given them-and that they
| exist in the atmosphere OF the sun. 1t is also
| known that, generally speaking, the same
pOrs, raised to high temperatures in laboratory
| experiments. are able TO produce lines agreeing
| with the dark lines in position, but bright in
stoad of dark. These vapors are then made to
| prove that they can absorb the same kind of
light which, under the same temperature, they
| can emit. Here, then, is a clue to the consti-
| tuition Of the universe. careful mapping of
| the lines, which exist in the spectrum by hun
| dreds. enables the astronomer to take the light
| of the far-away star. analyZe its rays, and, by
| comparison, safely state to the world the con-
| ditions of Its existence.
WHAT SCIENCE SAYS.
Should the reader exhibit surprise when as
tronomers say that this or that star was reced-
| ing from the solar system at rate Of thirty
miles per second, or that another star was APP
preaching at q greater rate, he could not be
blamed for his doubts. Apparently this is as
| Stunning too much. To measure the velocity of
light is delicate enough, indeed, but to boldly
declare that stars are approaching or receding
| is, unquestionably, insanity! But science does
say so in cases and is right within reasonable
limits Of error. Let return to the little
| "lines" in the colored band These lines af-
ford US not only the opportunity of sorting out