By EDGAR L. LARKIN, New Windsor Observatory, New Windsor, Illinois.
Within the past five years, scientific men have surpassed previous
efforts in close measurement and refined analysis. By means of
instruments of exceeding delicacy, processes in nature hitherto unknown,
are made palpable to sense. Heat is found in ice, light in seeming
darkness, and sound in apparent silence. It seems that physicists and
chemists have almost if not quite reached the ultimate atoms of matter.
The mechanism must be sensitive, as such properties of matter as heat,
light, electricity, magnetism, and actinism, are to be handled, caused
to vanish and reappear, analyzed and measured. With such instruments
nature is scrutinized, revealing new properties, strange motions,
vibrations, and undulations. Throughout the visible universe, the
faintest pulsations of atoms are detected, and countless millions of
infinitely small waves, bearing light, heat, and sound, are discovered
and their lengths determined. Refined spectroscopic analysis of light is
now made so that when any material burns, no matter what its distance,
its spectrum tells what substance is burning. When any luminous body
appears, it can be told whether it is approaching or receding, or
whether it shines by its own or reflected light; whence it is seen that
rays falling on earth from a flight of a hundred years, are as sounding
lines dropped in the appalling depths of space. We wish to describe a
few of these intricate instruments, and mention several far-reaching
discoveries made by their use; beginning with mechanism for the
manipulation of light. Optics is based on the accidental discovery that
a piece of glass of certain shape will draw light to a focus, forming an
image of any object at that point. The next step was in learning that
this image can be viewed with a microscope, and magnified; thus came the
telescope revealing unheard of suns and galaxies. The first telescopes
colored everything looked at, but by a hundred years of mathematical
research, the proper curvature of objectives formed of two glasses was
discovered, so that now we have perfect instruments. Great results
followed; one can now peer into the profound solitudes of space,
bringing to view millions of stars, requiring light 5,000 years to
traverse their awful distance, and behold suns wheeling around suns, and
thousands of nebulæ, or agglomerations of stars so distant as to send
us confused light, appearing like faint gauze like structures in
measureless voids. The modern telescope has astonishing power, thus:
When Mr. Clark finished the great twenty-six-inch equatorial, now at
Washington, he tested its seeing properties. A photographic calligraph,
whose letters were so fine as to require a microscope to see them, was
placed at a distance of three hundred feet. Mr. Clark turned the great
eye upon the invisible thing and read the writing with ease. But a
greater feat than this was accomplished by the same instrument-- the
discovery of the two little moons of Mars, by Prof. Asaph Hall, in 1877.
They are so small as to be incapable of measurement by ordinary means,
but with an ingenious photometer devised by Prof. Pickering of Harvard
College, he determined the outer satellite to be six and the inner seven
miles in diameter. The discovery of these minute bodies seems past
belief, and will appear more so, when it is told that the task is equal
to that of viewing a luminous ball two inches in diameter suspended
above Boston, by the telescope situated in the city of New York.
(Newcomb and Holden's Astronomy, p. 338.)
Phobos, the nearest moon, is only 4,000 miles from the surface of Mars,
and is obliged to move with such great velocity to prevent falling, that
it actually makes a circuit about its primary in only seven hours and
thirty-eight minutes. But Mars turns on _its_ axis in twenty-four hours
and thirty-seven minutes, so the moon goes round three times, while Mars
does once, hence it rises in the west and sets in the east, making one
day of Mars equal three of its months. This moon changes every two
hours, passing all phases in a single martial night; is anomalous in
the solar system, and tends to subvert that theory of cosmic evolution
wherein a rotating gaseous sun cast off concentric rings, afterward
becoming planets. Astronomers were not satisfied with the telescope;
true, they beheld the phenomena of the solar system; planets rotating on
axes, and satellites revolving about them. They saw sunspots, faculæ,
and solar upheaval; watched eclipses, transits, and the alternations of
summer and winter on Mars, and detected the laws of gravity and motion
in the system to which the earth belongs. They then devised the
micrometer. This is a complex mechanism placed in the focus of a
telescope, and by its use any object, providing it shows a disk, no
matter what its distance, can be measured. It consists of spider webs
set within a graduated metallic circle, the webs movable by screws, and
the whole instrument capable of rotating about the collimation axis of
the telescope. The screw head is a circle ruled to degrees and minutes,
and turns in front of a fixed vernier in the field of a reading
microscope. One turn of the screw moves the web a certain number
of seconds; then as there are 360° in a circle,
one-three-hundred-and-sixtieth of a turn moves the web one-three-hundred
and-sixtieth of the amount, and so on. Thus, when two stars are seen in
the field, one web is moved by the screw until the fixed line and the
movable one are parallel, each bisecting a star. By reading with the
microscope the number of degrees turned, the distance apart of the stars
becomes known; the distance being learned, position is then sought; the
observance of which led to one of the greatest discoveries ever made by
man. The permanent line of the micrometer is placed in the line joining
the north and south poles of the heavens, and brought across one of the
stars; the movable web is then rotated until it bisects the other, and
then the angle between the webs is recorded. Double stars are thus
measured, first in distance, and second, their position. After this, if
any movement of the stars takes place, the tell tale micrometer at once
detects it.
In 1780, Sir Wm. Herschel measured double stars and made catalogues with
distances and positions. Within twenty years, he startled intellectual
man with the statement that many of the fixed stars actually move--one
great sun revolving around another, and both rotating about their common
center of gravity. If we look at a double star with a small telescope,
it looks just like any other; using a little larger glass, it changes
appearance and looks elongated; with a still better telescope, they
become distinctly separated and appear as two beautiful stars whose
elements are measured and carefully recorded, in order to see if they
move. Herschel detected the motion of fifty of these systems, and
revolutionized modern astronomy. Astronomers soared away from the little
solar system, and began a minute search throughout the whole sidereal
heavens. Herschel's catalogue contained four hundred double suns, only
fifty of which were known to be in revolution. Since then, enormous
advance has been made. The micrometer has been improved into an
instrument of great delicacy, and the number of doubles has swelled to
ten thousand; six hundred and fifty of them being known to be binary,
or revolving on orbits--Prof. S. W. Burnham, the distinguished young
astronomer of the Dearborn Observatory, Chicago, having discovered eight
hundred within the last eight years. This discovery implies stupendous
motion; every fixed star is a sun like our own, and we can imagine these
wheeling orbs to be surrounded by cool planets, the abode of life, as
well as ours. If the orbit of a binary system lies edgewise toward us,
then one star will hide the other each revolution, moving across it and
appearing on the other side. Several instances of this motion are
known; the distant suns having made more than a complete circuit since
discovery, the shortest periodic time known being twenty-five years.
Wonderful as was this achievement of the micrometer, one not less
surprising awaited its delicate measurement. If one walks in a long
street lighted with gas, the lights ahead will appear to separate, and
those in the rear approach. The little spider lines have detected just
such a movement in the heavens. The stars in Hercules are all the time
growing wider apart, while those in Argus, in exactly the opposite part
of the Universe, are steadily drawing nearer together. This demonstrates
that our sun with his stately retinue of planets, satellites, comets,
and meteorites, all move in grand march toward the constellation
Hercules. The entire universe is in motion. But these revelations of the
micrometer are tame compared with its final achievement, the discovery
of parallax.
This means difference of direction, and the parallax of a star is the
difference of its direction when viewed at intervals of six months.
Astronomers observe a star to-day with a powerful telescope and
micrometer; and in six months again measure the same star. But meanwhile
the earth has moved 183,000,000 miles to the east, so that if the star
has changed place, this enormous journey caused it, and the change
equals a line 91,400,000 miles long as viewed from the star. For years
many such observations were made; but behold the star was always in the
same place; the whole distance of the sun having dwindled down to the
diameter of a pin point in comparison with the awful chasm separating
us from the stars. Finally micrometers were made that measured lines
requiring 100,000 to make an inch; and a new series of observations
begun, crowning the labors of a century with success. Finite man
actually told the distance of the starry hosts and gauged the universe.
When the parallax of any object is found, its distance is at once known,
for the parallax is an arc of a circle whose radius is the distance.
By an important theorem in geometry it is learned, that when anything
subtends an angle of one second its distance is 206,265 times its
own diameter. The greatest parallax of any star is that of Alpha
Centauri--nine-tenths of a second; hence it is more than 206,265 times
91,400,000 miles--the distance of the sun--away, or twenty thousand
billions of miles. This is the distance of the nearest fixed star, and
is used as a standard of reference in describing greater depths of
space. This is not all the micrometer enables man to know, When the
distance separating the earth from two celestial bodies that revolve
is learned, the distance between the two orbs becomes known. Then
the period of revolution is learned from observation, and having the
distance and time, then their velocity can be determined. The distance
and velocity being given, then the combined weights of both suns can be
calculated, since by the laws of gravity and motion it is known how much
weight is required to produce so much motion in so much time, at so much
distance, and thus man weighs the stars. If the density of these bodies
could be ascertained, their diameters and volumes would be known, and
the size of the fixed stars would have been measured. Density can never
be exactly learned; but strange to say, photometers measure the quantity
of light that any bright body emits; hence the stars cannot have
specific gravity very far different from that of the sun, since they
send similar light, and in quantity obeying the law wherein light varies
inversely as the squares of distance. Therefore, knowing the weight and
having close approximation to density, the sizes of the stars are nearly
calculated. The conclusion is now made that all suns within the visible
universe are neither very many times larger nor smaller than our own.
(Newcomb and Holden's Astronomy, p. 454.)
Another result followed the use of the micrometer: the detection of the
proper motion of the stars. For several thousand years the stars have
been called "fixed," but the fine rulings of the filar micrometer tell a
different story. There are catalogues of several hundred moving stars,
whose motion is from one-half second to eight seconds annually. The
binary star, Sixty-one Cygni, the nearest north of the equator, moves
eight seconds every year, a displacement equal in three hundred and
sixty years to the apparent diameter of the moon. The fixed stars have
no general motion toward any point, but move in all directions.
Thus the micrometer revealed to man the magnitude and general structure,
together with the motions and revolutions of the sidereal heavens. Above
all, it demonstrated that gravity extends throughout the universe. Still
the longings of men were not appeased; they brought to view invisible
suns sunk in space, and told their weight, yet the thirst for knowledge
was not quenched. Men wished to know what all the suns are made of,
whether of substances like those composing the earth, or of kinds of
matter entirely different. Then was devised the spectroscope, and with
it men audaciously questioned nature in her most secluded recesses. The
basis of spectroscopy is the prism, which separates sunlight into seven
colors and projects a band of light called a spectrum. This was known
for three hundred years, and not much thought of it until Fraunhofer
viewed it with a telescope, and was surprised to find it filled with
hundreds of black lines invisible to the unaided eye. Could it be
possible that there are portions of the solar surface that fail to send
out light? Such is the fact, and then began a twenty years' search to
learn the cause. The lines in the solar spectrum were unexplained until
finally metals were vaporized in the intense heat of the electric arc
and the light passed through a spectroscope, when behold the spectra of
metals were filled with bright lines in the same places as were the
dark lines in the spectrum of the sun. Another step: if when metals are
volatilized in the arc, rays of light from the sun are passed through
the vapor and allowed to enter the spectroscope, a great change is
wrought; a reversal takes place, and the original black bands reappear.
A new law of nature was discovered, thus: "Vapors of all elements absorb
the same rays of light which they emit when incandescent." Every element
makes a different spectrum with lines in different places and of
different widths. These have been memorized by chemists, so that when an
expert having a spectroscope sees anything burn he can tell what it is
as well as read a printed page. Men have learned the alphabet of the
universe, and can read in all things radiating light, the constituent
elements. The black lines in the solar spectrum are there because in the
atmosphere of the sun exist vapors of metals, and the light from the
liquid metals below is unable to pass through and reach the earth, being
absorbed kind for kind. Gaseous iron sifts out all rays emitted from
melted iron, and so do the vapors of all other elements in the sun,
radiating light in unison with their own. Sodium, iron, calcium,
hydrogen, magnesium, and many other substances are now known to be
incandescent in the sun and stars; and the results of the developments
of the spectroscope may be summed up in the generalization that all
bodies in the universe are composed of the same substance the earth is.
The sun is subject to terrific hurricanes and cyclones, as well as
explosions, casting up jets to the height of 200,000 miles. In the early
days of spectroscopy these protuberances could only be seen at a time
of a total solar ellipse, and astronomers made long journeys to distant
parts of the earth to be in line of totality. Now all is changed. Images
of the sun are thrown into the observatory by an ingenious instrument
run by clockwork, and called a heliostat. This is set on the sun at such
an angle as to throw the solar image into the objective of the telescope
placed horizontally in a darkened observatory, and the pendulum ball set
in motion, when it will follow the sun without moving its image, all day
if desired. At the eye end of the telescope is attached the spectroscope
and the micrometer, and the whole set of instruments so adjusted that
just the edge of the sun is seen, making a half spectrum. The other half
of the spectroscope projects above the solar limb, and is dark, so if an
explosion throws up liquid jets, or flames of hydrogen, the astronomer
at once sees them and with the micrometer measures their height before
they have time to fall. And the spectrum at once tells what the jets are
composed of, whether hydrogen, gaseous iron, calcium, or anything else.
Prof. C. A. Young saw a jet of hydrogen ascend a distance of 200,000
miles, measured its height, noted its spectrum and timed its ascent by
a chronometer all at once, and was astonished to find the velocity one
hundred and sixty miles per second--eight times faster than the earth
flies on its orbit. By these improvements solar hurricanes, whirlpools,
and explosions can be seen from any physical observatory on clear days.
The slit of the spectroscope can be moved anywhere on the disk of the
sun; so that if the observer sees a tornado begin, he moves the slit
along with it, measures the length of its tract and velocity. With the
telescope, micrometer, heliostat, and spectroscope came desire for more
complex instruments, resulting in the invention of the photoheliograph,
invoking the aid of photography to make permanent the results of these
exciting researches. This mechanism consists of an excessively sensitive
plate, adjusted in the solar focus of the telespectroscope. In front
of the plate in the camera is a screen attached to a spring, and held
closed by a cord. The eye is applied to the spectroscopic end of the
complex arrangement to watch the development of solar hurricanes.
Finally an appalling outburst occurs; the flames leap higher and higher,
torn into a thousand shreds, presenting a scene that language is
powerless to describe. When the display is at the height of its
magnificence, the astronomer cuts the cord; the slide makes an exposure
of one-three thousandth part of a second, and an accurate photograph
is taken. The storm all in rapid motion is petrified on the plate;
everything is distinct, all the surging billows of fire, boilings, and
turbulence are rendered motionless with the velocity of lightning.
At Meudon, in France, M. Janssen takes these instantaneous photographs
of the sun, thirty inches in diameter, and afterward enlarges them to
ten feet; showing scenes of fiery desolation that appalls the human
imagination. (See address of Vice President Langley, A. A. A. S.,
Proceedings Saratoga Meeting, p. 56.) This huge photograph can be viewed
in detail with a small telescope and micrometer, and the crests of solar
waves measured. Many of these billows of fire are in dimensions
every way equal in size to the State of Illinois. Binary stars are
photographed so that in time to come they can be retaken, when if they
have moved, the precise amount can be measured.
Another instrument is the telepolariscope, to be attached to a
telescope. It tells whether any luminous body sends us its own, or
reflected light. Only one comet bright enough to be examined has
appeared since its perfection. This was Coggia's, and was found to
reflect solar from the tail, and to radiate its own light from the
nucleus.
Still another intricate instrument is in use, the thermograph, that
utilizes the heat rays from the sun, instead of the light. It takes
pictures by heat; in other words, it sees in the dark; brings invisible
things to the eye of man, and is used in astronomical and physical
researches wherein undulations and radiations are concerned. And now
comes the magnetometer, to measure the amount of magnetism that reaches
the earth from the sun. It points to zero when the magnetic forces of
the earth are in equilibrium, but let a magnetic storm occur anywhere
in the world and the pointer will move by invisible power. It detects a
close relation between the magnetism of the earth and sun. The needle is
deflected every time a solar disturbance takes place. At Kew, England,
an astronomer was viewing the sun with a telescope and observed a tongue
of flame dart across a spot whose diameter was thirty-three thousand
seven hundred miles. The magnetometer was violently agitated at once,
showing that whatever magnetism may be, its influence traversed the
distance of the sun with a velocity greater than that of light.
Not less remarkable is the new instrument, the thermal balance,
devised by Prof. S. P. Langley, Pittsburgh. It will measure the
one-fifty-thousandth part of a degree of heat, and consists of strips
of platinum one-thirty-second of an inch wide and one-fourth of an inch
long; and so thin that it requires fifty to equal the thickness of
tissue paper, placed in the circuit of electricity running to a
galvanometer. "When mounted in a reflected telescope it will record the
heat from the body of a man or other animal in an adjoining field, and
can do so at great distances. It will do this equally well at night,
and may be said, in a certain sense, to give the power of seeing in
the dark." (_Science_, issue of Jan. 8,1881, p. 12.) It is expected to
reveal great facts concerning the heat of the stars.
Indeed, the thermopile in the hands of Lockyer has already made palpable
the heat of the fixed stars. He placed the little detective in the focus
of a telescope and turned it on Arcturus. "The result was this, that the
heat received from Arcturus, when at an altitude of 55°, was found to be
just equal to that received from a cube of boiling water, three inches
across each side, at the distance of four hundred yards; and the heat
from Vega is equal to that from the same cube at six hundred yards."
(Lockyer's Star Gazing, p. 385.) Thus that inscrutable mode of force
heat traverses the depths of space, reaches the earth, and turns the
delicate balance of the thermopile. Another discovery was made with the
spectroscope; thus, if a boat moves up a river, it will meet more waves
than will strike it if going down stream. Light is the undulation of
waves; hence if the spectroscope is set on a star that is approaching
the earth, more waves will enter than if set on a receding star, which
fact is known by displacement of lines in the spectroscope from normal
positions. It is found that many fixed stars are approaching, while
others are moving away from the solar system.
We cannot note the researches of Edison, Lockyer, or Tyndall, nor of
Crookes, who has seemingly reached the molecules whence the universe is
composed.
The modern observatory is a labyrinth of sensitive instruments; and when
any disturbance takes place in nature, in heat, light, magnetism, or
like modes of force, the apparatus note and record them.
Men are by no means satisfied. Insatiable thirst to know more is
developing into a fever of unrest; they are wandering beyond the limits
of the known, every day a little farther. They survey space, and
interrogate the infinite; measure the atom of hydrogen and weigh suns.
Man takes no rest, and neither will he until he shall have found his own
place in the chain of nature.--_Kansas Review_.
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