interest in the science, and aroused an intense desire to provide
serviceable instruments, and to establish buildings suitable for
their care and use. To Williams College, Massachusetts, belongs the
honor of erecting, in 1836, the first astronomical observatory on
this continent. Under its revolving dome was mounted an Herschelian
telescope of ten feet focus, which later became the property of
Lafayette College, where it is still preserved. In 1843, John Quincy
Adams laid the corner-stone of the Longworth Observatory in Cincinnati,
and delivered a commemorative address, his last great oration. The
construction of the United States Naval Observatory at Washington soon
followed, and before 1850 there were fourteen observatories established
in this country. Nearly all the instruments they contained were made
abroad, chiefly in Munich and London. Since then the number has risen
to two hundred recognized observatories, of which twenty-four are of
superior order, where systematic work is daily pursued, and the results
are regularly published in book form. About two hundred observatories
exist in other nations.
VII. IMPROVED INSTRUMENTS; THEIR EFFECT ON THE SCIENCE.
The great improvements in telescopes made during the century have been
fruitful in two ways; a better knowledge of the surface of the moon and
of the planets has been gained, and we have been enabled to learn with
precision the exact motions and times of revolution of these bodies
and of their accompanying moons. This information, by the use of the
laws ascertained by Kepler and La Place, gives us their exact distance,
dimensions, and mass. With the increase of telescopic power, the census
of the starry host has been so augmented that the number of stars
within reach of our modern instruments exceeds 125,000,000. But we had
gone little beyond this sort of information until the invention of the
spectroscope.
Previous to the year 1859 a few meteors, composed chiefly of stone
or iron, some of which had been actually seen to fall from the sky,
had been subjected to chemical analysis; but outside of this naught
was known of the physical constitution of other worlds than ours. Our
ignorance on this point was complete. All our attempts to become better
acquainted with the structure of the planets, the composition of the
sun, and the nature of the fixed stars would probably have been in vain
but for the invention of the spectroscope. This surprising instrument
is a master-key with which to unlock many of Nature’s mysteries; her
recesses are brought to view, and the farthest star is subjected to an
accurate chemical analysis, so far as the light that comes from it is
sufficient to disclose the materials of which it is composed.
[Illustration: THE LICK OBSERVATORY, MOUNT HAMILTON, CALIFORNIA.]
The wondrous use of electricity as an agent for the production of
light, heat, and power is no greater achievement, in its way, than is
Spectrum Analysis in bringing to our earthly laboratories the work of
the Divine Hand performed in distant regions of space. Yet the story
of the spectroscope is easily told. In its essential elements it is
merely this: A ray of light, entering a darkened room through a hole
in the window shutter, produces a bright beam on the opposite wall. A
triangular glass prism held close to the crevice turns this beam into a
band of rainbow hues. If the hole can be changed into a small slit, say
one fourth of an inch high and one fiftieth of an inch wide, and if the
light can further be made to pass in succession through several prisms,
instead of through one, the band will be so elongated thereby that its
various and surprising markings can be thoroughly traced and fully
studied.
[Illustration: THE SPECTROSCOPE.]
To this band of bright colors Sir Isaac Newton gave the name of the
solar spectrum. The image formed by the light of any luminous body,
after it has passed through a prism, is said to be the spectrum of that
body.
VIII. THE SPECTROSCOPE AND ITS TRIUMPHS.
The spectroscope consists essentially of three tubes joined in the
form of the letter Y, one of which is a small telescope, in the focus
of which a narrow slit is placed to admit the ray of light that is to
be examined; a prism, or a ruled grating that disperses the light, so
as to form a spectrum; and a view telescope, with which to observe the
various parts of the spectrum.
By using a small telescope to view the spectrum of the sun, Fraunhofer,
a German optician, in 1814, discovered that the whole length of
the spectrum was crowded with dark lines, very narrow, indeed, but
scattered all through the seven hues. He found that sunlight, whether
taken directly or reflected from clouds or from the moon or planets,
invariably gave the same spectrum; but in no case did light from the
stars give a spectrum of the same sort as that from the sun.
[Illustration: YERKES TELESCOPE, UNIVERSITY OF CHICAGO.
Largest in the World.]
Dr. Kirchhoff, of Heidelberg, in 1859, explained the origin of the
dark lines, and showed that there are three kinds of spectra: first,
that of an incandescent solid or liquid, which is always perfectly
continuous, showing neither dark lines nor bright; second, the spectrum
of a glowing gas, which consists of bright lines or bands separated by
dark spaces. These lines are characteristic of the chemical elements
that cause them; and so, from the composition of the bright lines in
a spectrum, it is possible to tell their origin. Third, a spectrum
crossed by dark lines; which occurs when an incandescent solid is
viewed through absorbent vapors.
In the solar eclipse of 1868, M. Janssen first noticed that the solar
prominences gave a spectrum of the second kind, and thus proved that
the prominences consist of glowing gas. Since that time the march of
discovery has been exceedingly rapid.
This simple instrument has thus led the way to a knowledge of the
elements composing every heavenly body, no matter what its distance,
provided only it is giving out light intense enough to reach our gaze.
For the perfection both of the telescope and spectroscope we owe
much to the optical skill and mechanical dexterity of the Clarks and
Rowland, Hastings and Brashear, all Americans.
About forty chemical elements have now been recognized in the sun.
The most prominent are iron, calcium, hydrogen, nickel, and sodium.
A distortion, or displacement, of some of the lines in the spectrum
enables us to calculate the speed at which the gases are rushing toward
or from us. A given line in the spectrum of Aldebaran is displaced
toward the violet in such a way as to show that the star is approaching
the sun at the rate of thirty miles a second; while a similar line, in
the case of Altair, so deviates toward the red end of the spectrum as
to prove that it is receding from the solar system at a velocity of
twenty-four miles a second. By this principle, recognized by Doppler in
1842, the motions of about one hundred stars toward or from the solar
system have been ascertained.
There is no question but that the solar system, as a whole, is steadily
moving away from Sirius, and toward the constellation of Hercules;
whether faster than at a rate of twelve miles every second is still
scarcely decided; but this rate would be about a million miles a day,
or three hundred and seventy million miles a year.
IX. WHAT IS DONE IN A LARGE OBSERVATORY; ITS WORK.
A visitor who wants to know what is done in a great observatory might
go to Harvard some evening. He would probably find the large refractor
pointed toward the satellites of Jupiter, Uranus, or Neptune, with a
view of noting their precise places, so as to compute tables of their
exact motions; or he might find a laborious observer watching such
double stars as have considerable proper motion, and making drawings of
conspicuous nebulæ, so that future astronomers may be able to decide
whether time has wrought any changes in their constitution or figure.
The great glass at Princeton, under the charge of Professor Charles A.
Young, is largely used for spectroscopic work, examining the sun’s
photosphere by day, and noting the spectra of the stars at night.
Spectral observation is an important part of the routine at the Yerkes
Observatory in Wisconsin.
Many faint comets have been successfully photographed at the Lick
Observatory, on Mount Hamilton, California, and elsewhere by the use of
very sensitive plates and a long exposure.
S. W. Burnham, of Chicago, is famed for his acuteness of vision, tested
in having detected and measured over one thousand double stars which
to other eyes had appeared only as single stars. The discovery of
these objects belongs wholly to the nineteenth century; for in 1803,
Sir William Herschel first announced the existence of sidereal systems
composed of two stars, one revolving around the other, or both moving
about a common centre. Some of these binary systems have periods of as
great a length as fifteen hundred years; and some are as brief as four,
and even two days. Some of them afford curious instances of contrasted
colors, the larger star red or orange, and the smaller star blue or
green.
X. THE NATIONAL OBSERVATORY AT WASHINGTON.
[Illustration: PROFESSOR WILLIAM HARKNESS,
Astronomical Director U. S. Naval Observatory, Washington, D. C.]
Professor William Harkness, U. S. N., M. D., LL. D., is widely known
as the author of numerous astronomical and physical papers and books.
He has also designed a number of instruments and made important
discoveries. He has long been connected with the United States Naval
Observatory, and now holds the position of Astronomical Director. His
report for the year 1898 shows that the twenty-six inch reflector at
Washington is now nightly engaged in mapping the relative positions of
Rhea and Iapetus, the fifth and eighth satellites of Saturn, with the
intention of securing a new and final determination of the mass of that
planet, which has been heretofore reckoned as one 3492d of the sun.
The twelve-inch telescope is chiefly employed in studying comets and
asteroids, and on Thursday evenings is at the service of the public. In
the year 1898, 3778 observations were made with the nine-inch transit
circle, for which two men were detailed, with the services of five
computers.
A transit circle and an altazimuth instrument, each turned out of
solid steel, have recently been added to the equipment, and are of a
workmanship that compares favorably with anything ever manufactured
in Europe. It is asserted that the latter instrument will give more
accurate measurements of declination than a transit circle, which is an
innovation on long-cherished ideas.
Professor Simon Newcomb, of the United States Navy, is about to
issue new tables of Mars, Uranus, and Neptune, and a “Catalogue of
Fundamental Stars for the Epoch 1900.” During the year 1898 three
thousand copies of the American Nautical Almanac were published. This
is but an illustration of the scientific labor accomplished at this
busy hive of industry. During the year this observatory issued to
the navy 230 chronometers, 200 sextants and octants, and 1400 other
nautical instruments of value.
XI. STAR MAPS AND CATALOGUES.
In the year 128 B. C. Hipparchus put out a catalogue of 1025 stars
observed at Rhodes. Twenty such works succeeded this up to the year
1801, when Lalande, of Paris, brought out a list of 47,390 stars. It
will be remembered that few stars have names, except those known to the
Arabians of old, but are designated by their positions in the heavens.
It is customary to refer to them by their declinations and right
ascensions, as so many degrees north or south of the celestial equator,
and so many degrees, or hours, east of the vernal equinox—fifteen
degrees being the equivalent of an hour of right ascension—just like
the latitude and longitude of cities on a common globe.
During the nineteenth century many celestial atlases and astronomical
catalogues have been published. These contain lists of comets and
nebulæ, and the places of the double stars and of the fixed stars. Of
the latter alone over one hundred have appeared, of which Argelander’s
is by far the largest, as it contains the places of more than 310,000
stars. The catalogue prepared by the British Association in 1845 is
of great value, containing 8377 stars. Yarnall’s, of 10,658 stars,
published in Washington in 1873, is most accessible to us.
Professor C. H. F. Peters, of the Hamilton College Observatory,
Clinton, N. Y., the discoverer of so many asteroids, has prepared a
valuable series of star charts. By dividing the heavens into small
squares and carefully photographing each of them, the places of a vast
number of stars can be recorded with far greater accuracy than by the
old plan of a separate instrumental measurement of the position of the
stars. By the use of microscopes the determination of their positions
can be made with precision. These plates are preserved with care, and
when those of the same region of the skies, made in different years,
are compared, any variation in the relative positions of the objects
can be detected with certainty. The perfection of this method of
star-mapping is justly deemed one of the most important achievements of
the century.
For an amateur star-gazer who is not provided with a set of maps,
Whitall’s Planisphere is a very ready aid, as it can be instantly
adjusted to any day and hour. The inexperienced, and those who have no
instruments, can use it with ease and satisfaction to locate a thousand
of the most conspicuous stars.
XII. ASTRONOMICAL BOOKS AND THEIR WRITERS.
In England this attractive study has been popularized chiefly by the
interesting works of the two Herschels, who were voluminous writers,
the lectures of Proctor, and the admirable compend of facts so
assiduously gathered by G. F. Chambers in his delightful treatise on
astronomy.
In our own country the heights of theoretical astronomy have been
scaled by such minds as Benjamin Pierce, the profound mathematician of
Harvard University; James C. Watson, of Ann Arbor, whose early death
was a great loss to science; and Simon Newcomb, the genial savant
of Washington. Chauvenet and Loomis have taught us the meaning of
practical astronomy; and Olmsted, Young, Todd, and not a few others of
distinction have prepared text-books that fully present the elements of
the science.
Nor is this fascinating study limited to the students of the 484
colleges and universities of the land. The last report of the United
States Commissioner of Education shows that in the public and private
high schools of the nation there are over nine thousand boys and
sixteen thousand girls pursuing the study of astronomy.
XIII. THE PRACTICAL USES OF ASTRONOMY AS AN AID TO NAVIGATION AND
GEODESY.
The practical value of this science is best appreciated by the
navigator, who sees in the sun and moon his clock, and in the stars and
planets the ready means of learning his latitude and longitude. It is
one of the first tasks of the midshipman to become familiar with the
use of the sextant, by which he works out the problem of ascertaining
the exact place of the ship upon the ocean. Navigation is helpless
without the assistance of astronomy. Yet it is only the A, B, C of the
science that the sailor has any use for; its higher mysteries are away
beyond his needs and of no practical profit to him.
Nathaniel Bowditch, of Salem, Mass., in 1802, issued a book entitled
“The New American Practical Navigator,” which is still a standard
treatise for seamen. His rare acquirements as a mathematician were
signally displayed, and in a form that has proved enduring, when, in
1814–17, he translated into English, accompanied with copious notes of
his own, the profound work, “Celestial Mechanics,” penned by the gifted
La Place in 1799. Although in name a translation of a foreign book with
a commentary, it is in many respects an original work. Professor Elias
Loomis, who left to Yale University three hundred thousand dollars as
an endowment fund to aid in prosecuting astronomical research, said of
him, in 1850, “Bowditch has probably done more for the improvement of
physical astronomy than all other Americans combined.” Dr. Bowditch
published the work in four ponderous quarto volumes wholly at his own
private cost. These volumes he did not expose for sale, but generously
gave them to such persons as proved to him their ability to appreciate
and comprehend them. This outlay impaired the fortunes of his family,
but became his own unique monument.
This work remains one of the most profound efforts of mathematical
research on record. Bowditch’s accuracy has passed into a proverb.
He gave the latitude of all the principal seaports of the world with
marked precision; while some of the longitudes are now found to be
slightly in error, it is surprising that his determinations of those of
Boston and Philadelphia should be exactly the same as those obtained by
the best methods in use to-day. But he makes San Francisco and Halifax
seven miles too far to the east, and New York eight miles too far west.
But we are to remember that for this computation the best available
instruments were the chronometers of a century ago, and that lunar
observations were made with the old-time sextant.
[Illustration: ZENITH TELESCOPE.
Made for University of Pennsylvania by Warner & Swasey.]
As applied to geodesy, astronomy has added a process of ascertaining
geographical latitude with marvelous accuracy and speed by the use of
the zenith telescope, an instrument devised by Major Talcott in 1835.
This instrument can be set in a vertical direction with ease, and be
pointed alternately to two stars that cross the meridian at a brief
interval of time, the one north and the other south of the zenith.
Difficulties that arise from refraction are avoided, and the resulting
latitude is quickly computed. This method is largely employed in the
surveys of the public lands, as also in establishing the boundary
between the United States and British America.
XIV. NOTABLE EPOCHS IN THE NINETEENTH CENTURY.
Worth marking as epochs of the nineteenth century were such dates
as October 10, 1846, when the first determination of difference of
longitude of two places was made by the use of the telegraph wire.
Sears C. Walker, in Washington, and E. Otis Kendall, in Philadelphia,
compared their clocks by interchanging telegraphic signals, and thus
found their respective longitudes.
In 1850, Professor William C. Bond, of Harvard College, invented the
chronograph. Through the urgency of Sir David Brewster, it was shown
in the great exhibition of that year in London, where a medal was
awarded for it. The chronograph was speedily adopted throughout Europe,
and together with other apparatus made by Bond constituted what there
became known as the “American method” of recording observations.
Through it the errors for which the “personal equation” is a partial
remedy are largely eliminated, and a superior definiteness of record is
obtained.
On August 7, 1869, the first application of the spectroscope to
the examination of the corona of the sun was the beginning of the
revelation of the inner mysteries of the constitution and activities
of the great luminary. The transit of Venus that occurred on December
6, 1882, was fruitful in measurements, by which the estimates of the
distance of the sun were reduced from the long-accepted figures, 95 to
92 millions of miles. Yet this loss of three millions of miles resulted
from the apparently trifling change of reckoning the sun’s parallax at
8.82″, instead of 8.57″. An occurrence of vast practical advantage to
the whole nation was that of November 18, 1883, when the four standard
meridians of railroad time were adopted and put into use. From that
day the clocks of the Union were set to keep either Eastern, Central,
Mountain, or Pacific Coast time.
Professor Edward E. Barnard had used the magnificent telescope of
thirty-six inches aperture, belonging to the Lick Observatory in
California, but a short time before he astonished the world by
discovering a fifth satellite of Jupiter, although it appeared as but
a faint speck of light. Besides other honors for this achievement, in
1894 the French Academy of Sciences awarded him the Arago medal, of the
value of a thousand francs, a distinction given but twice before, first
to Le Verrier, for the discovery of Neptune in 1846, and to Asaph Hall,
for finding the two moons of Mars in 1877.
“Personal equation” is the name given to the amount of error to which
any person is habitually liable in attempting to note the time of a
fixed occurrence. When the astronomer looks at a star passing the
cross-wires of his transit, he is likely to make the record one or
two tenths of a second after the true time, or possibly a like small
amount of time before the actual occurrence, by anticipation. This is
not a matter of wrong intention, nor due to willfulness. But in precise
observations, especially where comparisons are to be made between the
records of several persons, the “personal equation” must be determined,
if possible, and allowed for. Various methods of correcting this
inaccuracy have been used. But the best is that of Frank H. Bigelow,
of the Nautical Almanac Office, Washington, who, in 1890, devised a
process of taking star transits by photography. It entirely does away
with this source of error, and has proved of great value.
XV. DISCARDED DOCTRINES AND ABANDONED IDEAS.
A few generations ago an eight-day clock was to be found only in the
homes of well-to-do people, and a gold watch was a symbol of wealth,
such as to subject its wearer to a special tax. In this age of dollar
clocks and Waterbury watches, almanacs are no longer indispensable. We
do not regulate our time-pieces by the rising and setting of the sun;
nor can a future Jay Gould lay the foundation of his fortune, as did
the one best known by that name, by setting up rural noon-marks for a
fixed fee.
Some pleasant dreams of past decades have vanished in the light of
recent knowledge. The nebular hypothesis, that wondrous conception of
Swedenborg, elaborated by La Place and espoused by William Herschel and
so many others, as affording a full explanation of the method by which
our worlds were shaped into their present forms, has ceased to have
general acceptance. M. Maedler, director of the Dorpat Observatory in
1846, had a firm persuasion that the collective body of stars visible
to us has a movement of revolution about a centre situated in the group
of the Pleiades, and corresponding to the star Alcyone. But this notion
of a central sun around which all the solar system is circling has lost
ground.
The distortion in the orbit of the planet Mercury has been accounted
for by the urgent suggestion that there must be some planet, as yet
undiscovered, that disturbs the regularity of Mercury’s movements, but
whose orbit is so near to the sun as to baffle all ordinary efforts to
see it. It has received, by anticipation, the prenatal name of Vulcan.
Many eyes have peered most intently into the region indicated, and
some few have imagined they had found what they sought. A physician
of the village of Orgeres, France, M. Lescarbault by name, on March
20, 1859, saw such an object pass over the sun’s disk. The skillful Le
Verrier was much impressed by this physician’s minute account of the
occurrence. But there was no confirmation of the alleged discovery.
At the time of subsequent eclipses that part of the heavens has been
repeatedly examined closely, but in vain. So we must wait longer before
believing that Vulcan does exist.
When, in 1877, Professor Hall, through the powerful telescope at
Washington, saw that Mars was attended by two tiny satellites, he put a
permanent injunction on the further use of the once favorite phrase,
“The snowy poles of moonless Mars.”