The development of telescopic power within the present century is one
of the most striking examples of intellectual progress and mastery in
the history of mankind. The first day of the century found us, not,
indeed, where we were left by Galileo and Copernicus in the knowledge
of the skies and in our ability to penetrate their depths, but it did
find us advanced by only moderate stages from the sky-lore of the
past.
The after half of the eighteenth century presents a history of
astronomical investigation and deduction which confirmed and amplified
the preceding knowledge; but that period did not greatly widen the
field of observation. If the sphere of space which had been explored
on the first day of January, 1801, could be compared with that which
is now known and explored by our astronomers, the one sphere would be
to the other even as an apple to the earth.
It is difficult to apprehend the tremendous strides which we have made
in the production of telescopes and the consequent increase in our
sweep of the heavens. It was only in 1774 that the elder Herschel
began his work in the construction of reflecting telescopes. These he
gradually increased in size, until near the close of the century, when
he produced an instrument which magnified two hundred and twenty-seven
diameters. In the course of his career he built two hundred
telescopes, having a seven-foot focus; 150 of ten feet and about
eighty of twenty feet each.
With these instruments the astronomical work in the last quarter of
the eighteenth century was mostly performed. The study of the heavens
at this epoch began to reach out from the planetary system to the
fixed stars. In this work Herschel led the way. The planet Uranus at
first bore the name of Herschel, from its discoverer. Sir John
Herschel, son of Sir William, was born in 1792. All of his
astronomical work was accomplished in our century. Following the line
of his father, he used the reflecting telescope, and it was an
instrument of this kind that he took to his observatory at the Cape of
Good Hope. Lord Rosse was born in the year 1800. Under his auspices
the reflecting telescope reached its maximum of power and usefulness.
His great reflector, built in his own grounds at Birr Castle, Ireland,
was finished in 1844. This instrument was the marvel of that epoch. It
had a focal distance of fifty-three feet, and an aperture of six feet.
With this great telescope its master reached out into the region of
the nebulæ, and began the real work of exploring the sidereal heavens.
In the reflecting telescope, however, there are necessary limitations.
Before the middle of this century, it was known that the future of
astronomy depended upon the refracting lens, and not on the speculum.
The latter, in the hands of the two Herschels and Rosse, had reached
its utmost limits--as is shown by the fact that to this day the Rosse
telescope is the largest of its kind in the world.
Meanwhile the production of refracting telescopes made but slow
progress. As late as 1836 the largest instrument of this kind in the
world was the eleven-inch telescope of the observatory at Munich. The
next in importance was a nine and a half-inch instrument at Dorpat, in
Russia. This was the telescope through which the astronomer Struve
made his earlier studies and discoveries. His field of observation was
for the most part the fixed and double stars. At this time the largest
instrument in the United States was the five-inch refractor of Yale
College. Soon afterward, namely, in 1840, the observatory at
Philadelphia was supplied with a six-inch refracting telescope from
Munich.
German makers were now in the lead, and it was not long until a Munich
instrument having a lens of eleven inches diameter was imported for
the Mitchell Observatory on Mount Adams, overlooking Cincinnati. About
the same time a similar instrument of nine and a half inches aperture
was imported for the National Observatory at Washington. To this
period also belongs the construction of the Cambridge Observatory,
with its fifteen-inch refracting telescope. Another of the same size
was produced for the Royal Observatory at Pulkova, Russia. This was in
1839; and that instrument and the telescope at Cambridge were then the
largest of their kind in the world.
The history of the telescope-making in America properly begins with
Alvan Clark, Sr., of Cambridgeport, Massachusetts. It was in 1846 that
he produced his first telescope. Of this he made the lens, and such
was the excellence of his work that he soon became famous, to the
degree that the importation of foreign telescopes virtually ceased in
the United States. Nor was it long until foreign orders began to
arrive for the refracting lenses of Alvan Clark & Sons. The fame of
this firm went out through all the world, and by the beginning of the
last quarter of the century the Clark instruments were regarded as the
finest ever produced.
We cannot here refer to more than a few of the principal products of
Clark & Sons. Gradually they extended the width of their lenses,
gaining with each increase of diameter a rapidly increasing power of
penetration. At last they produced for the Royal Observatory of
Pulkova a twenty-seven-inch objective, which was, down to the early
eighties, the master work of its kind in the world. It was in the
grinding and polishing of their lenses that the Clarks surpassed all
men. In the production of the glass castings for the lenses, the
French have remained the masters. At the glass foundry of Mantois, of
Paris, the finest and largest discs ever produced in the world are
cast. But after the castings are made they are sent to America, to be
made into those wonderful objectives which constitute the glory of the
apparatus upon which the New Astronomy relies for its achievements.
It was in the year 1887 that the Lick Observatory on Mount Hamilton,
of the Coast Range in Southern California, was completed. The lens of
this instrument is thirty-six inches in diameter. Nor will the reader
without reflection readily realize the enormous stride which was made
in telescopy when the makers advanced from the twenty-seven-inch to
the thirty-six-inch objective. Lenses are to each other in their power
of collecting light and penetrating apace as the squares of their
diameters, and in the extent of space explored as the cubes of their
diameters.
The objective of the Pulkova instrument is to that of the Lick
Observatory as 3 is to 4. The squares are as 9 is to 16, and the cubes
are as 27 is to 64. This signifies that the depth of space penetrated
by the Lick instrument is to that of its predecessor as 16 is to 9,
and that the astronomical sphere resolved by the former is to the
sphere resolved by the latter as 64 is to 27--that is, the Lick
instrument at one bound revealed a universe _more than twice as great_
as all that was known before! The human mind at this one bound found
opportunity to explore and to know a sidereal sphere more than twice
as extensive as had ever been previously penetrated by the gaze of
man.
Nor is this all. The ambition of American astronomers and American
philanthropists has not been content with even the prodigious
achievement of the Lick telescope. In recent years an observatory has
been projected in connection with the University of Chicago, which has
come almost to completion, and which will bear by far the largest
telescopic instrument in the world. The site selected for the
observatory is seventy-five miles from the city, on the northern shore
of Lake Geneva. There is a high ground here, rising sufficiently into
a clear atmosphere, nearly two hundred feet above the level of the
lake.
The observatory and the great telescope which constitutes its central
fact are to bear the name of the donor, Mr. Yerkes, of Chicago, who
has contributed the means for rearing this magnificent adjunct of the
University. The enterprise contemplated from the first the
construction of the most powerful telescope ever known. The
manufacture of the objective, upon which everything depends, was
assigned to Mr. Alvan G. Clark, of Cambridgeport, Massachusetts, who
is the only living representative of the old firm of Alvan Clark &
Sons.
Alvan G. Clark has inherited much of the genius of his father, though
it is said that in making the lens of the Lick Observatory the father
had to be called from his retirement to superintend personally some of
the more delicate parts of the finishing before which task his sons
had quailed. But the younger Clark readily agreed to make the Geneva
lens, under the order of Yerkes, and to produce a perfect objective
_forty inches in diameter_! This important work, so critical--almost
impossible--has been successfully accomplished.
The making and the mounting of the Yerkes telescope have been assigned
to Warner & Swasey, of Cleveland, Ohio, who are recognized as the best
telescope builders in America. The great observatory is approaching
completion. The instrument itself has been finished, examined,
accepted by a committee of experts, and declared to fulfill all of the
conditions of the agreement between the founder and the makers. Thus,
just north of the boundary line between Illinois and Wisconsin, the
greatest telescope of the world has been lifted to its dome and
pointed to the heavens.
The formal opening of the observatory is promised for the summer
months of 1896. The human mind by this agency has made another stride
into the depths of infinite space. Another universe is presently to be
penetrated and revealed. A hollow sphere of space outside of the
sphere already known is to be added to the already unthinkable
universe which we inhabit. Every part of the immense observatory and
of the telescope is of American production, with the single important
exception of the cast glass disc from which the two principal lenses,
the one double convex and the other plano-concave, are produced. These
were cast by Mantois, of Paris, whose superiority to the American
manufacturers of optical glass is recognized.
It is estimated that the Yerkes telescope will gather three times as
much light as the twenty-three-inch instrument of the Princeton
Observatory. It surpasses in the same respect the twenty-six-inch
telescope at the National Observatory in the ratio of two and
three-eighths to one. It is in the same particular one and four-fifth
times as powerful as the instrument of the Royal Russian Observatory
at Pulkova; and it surpasses the great Lick instrument by twenty-three
per cent.
What the practical results of the study of the skies through this
monster instrument will be none may predict. Theoretically it is
capable of bringing the moon to an apparent distance of sixty miles.
Under favorable circumstances the observer will be able to note the
characteristics of the lunar landscape with more distinctness than a
good natural eye can discern the outlines and character of the summit
of Pike's Peak from Denver. The instrument has sufficient power to
reveal on the lunar disc any object five hundred feet square. Such a
thing as a village or even a great single building would be plainly
discernible.
Professor C.A. Young has recently pointed out the fact that the Yerkes
telescope, if it meets expectation, will show on the moon's surface
with much distinctness any such object as the Capitol at Washington.
It is complained that in America wealth is selfish and self-centred;
that the millionaire cares only for himself and the increase of his
already exorbitant estate. The ambition of such men as Lick of San
Jose and Yerkes of Chicago, seems to ameliorate the severe judgment of
mankind respecting the holders of the wealth of the world, and even to
transform them from their popular character of enemies and misers into
philanthropists and benefactors.