OPTICS.
EARLY TELESCOPES--THE LICK TELESCOPE--THE GRANDE LUNETTE--THE
STEREO-BINOCULAR FIELD GLASS--THE MICROSCOPE--THE SPECTROSCOPE--
POLARIZATION OF LIGHT--KALEIDOSCOPE--STEREOSCOPE--RANGE FINDER--
KINETOSCOPE AND MOVING PICTURES.
“And God said, Let there be light: and there was light. And God saw the
light that it was good; and God divided the light from the darkness.”
Thus early in the account of the creation is evidenced man’s
appreciation of the value of vision. Of all the senses which place man
in intelligent relation to his environment none is so important as
sight. More than all the others does it establish our relation to the
material world. When the babe is born, and its little emancipated soul
is brought in contact with the world, its wondering gaze sees the
panorama of visible things touching its eyes, and it stretches forth its
tiny arms in the vain effort to pluck the stars, apparently within its
reach. Distance and time add their values to light and vision, and as
his life expands to greater fullness, the perspective of his existence
creeps into his consciousness, and he finds himself farther away, but
still peering beyond into the infinity of distance, searching for the
visible evidence of knowledge. From the earliest times man learned to
spurn the groveling things of earth, and to delight his soul with the
marvelous infinity of the sky and its heavenly bodies. _Nunc ad astra_
was his ambitious cry, and in no field has his quest for knowledge been
more skillfully directed, faithfully maintained, or richly rewarded than
in the study of astronomy. Many important discoveries in this field have
been made in the Nineteenth Century, among which may be named the
discovery of the planet Neptune by Adams, Leverrier and Galle in 1846;
the satellites of Neptune in 1846, and those of Saturn in 1848 by Mr.
Lassell; the two satellites of Mars by Prof. Asaph Hall in 1877; and the
discovery of the so-called canals of Mars by Schiaparelli in 1877. But
the purpose of this work is to deal with material inventions rather than
scientific discoveries, and the leading invention in optics is the
telescope.
Who invented the telescope is a question that cannot now be answered.
For many years Galileo was credited in popular estimation with having
made this invention in 1609. But it is now known that, while he built
telescopes, and discovered the mountains of the moon, the spots on the
sun’s disk, the crescent phases of Venus, the four satellites of
Jupiter, the rings of Saturn, and made the first important astronomical
observations, the invention of the telescope, as an instrument, could
not be rightly claimed for him. Borelli credits it to Jansen &
Lippersheim, spectacle makers, of Middelburg, Holland, about 1590;
Descartes credits it to James Metius; Humboldt says Hans Lippershey (or
Laprey), a native of Wesel and a spectacle maker of Middelburg in 1608,
naming also Jacob Adriansz, sometimes called Metius and also Zacharias
Jansen.
The great impetus given to the study of astronomy by Galileo, in 1609,
was followed up by Huygens in 1655 with his improvement, by Gregory’s
reflecting telescope of 1663, and Newton’s in 1668. In 1733 Chester More
Hall invented the achromatic object glass of crown and flint glass. In
1758 John Dolland reinvented and introduced the same in the manufacture
of telescopes. In 1779 Herschel built his reflecting telescope, and in
March, 1781, he discovered the planet Uranus. In 1789 he built his great
reflector. It was while the latter telescope was exploring the heavens
that the Nineteenth Century began, and in the early part of this century
Herschel laid before the Royal Society a catalogue of many thousand
nebulæ and clusters of stars. Among the great telescopes of the
Nineteenth Century may be mentioned that made in London in 1802 for the
observatory of Madrid, which cost £11,000; the great reflecting
telescope of the Earl of Rosse, erected at Parsonstown, in Ireland, in
1842-45. This was 6 feet diameter, 54 feet focal length, and cost over
£20,000; the magnificent equatorial telescopes set up at the National
Observatories at Greenwich and Paris in 1860; Foucault’s reflecting
telescope at Paris, 1862, whose mirror was 31½ inches diameter, and
focal length 17¾ feet; Mr. R. S. Newall’s telescope, set up at Gateshead
by Cookes, of York, in 1870; object glass, 25 inches, tube, 30 feet; Mr.
A. Ainslie Common’s reflecting telescope, Ealing, Middlesex, 1879,
mirror, 37½ inches diameter, tube, 20 feet; the telescope at the United
States Observatory, at Washington, 1873, object glass, 26 inches, tube,
33 feet long; and the large refracting telescope by Howard Grubb, at
Dublin, for Vienna, 1881.
[Illustration: FIG. 194.--TELESCOPE AT LICK OBSERVATORY.]
In more recent times the great refracting telescope by Alvan Clark &
Sons, for the Lick Observatory on Mount Hamilton, California, in 1888,
attracted attention as superior to anything in existence up to that
time. This is shown in Fig. 194. The supporting column and base are of
iron, weighing twenty-five tons. This rests on a masonry foundation,
which forms the tomb of James Lick, its founder. The tube is 52 feet
long, 4 feet diameter in the middle, tapering to a little over 3 feet at
the ends. The object glass is 36 inches in diameter, and weighs, with
its cell, 530 lbs. The steel dome is 75 feet 4 inches in diameter, and
the weight of its moving parts is 100 tons. This instrument was
perfectly equipped with all gauges, scales, photographic and
spectroscope accessories, and fulfilled the condition imposed in the
trust deed of James Lick, of being “superior to and more powerful than
any telescope made.” It is a giant among instruments of precision, and
its ponderous aspect still asserts the dignity of its purpose, and
impresses even the frivolous visitor with a silent and thoughtful
respect.
It is not to be understood, however, that the great Lick telescope still
maintains its supremacy. The Yerkes telescope, which was exhibited at
the World’s Fair Exposition in 1893, at Chicago, had an object glass of
3.28 feet in diameter and a focal distance of 65 feet, and it moved
around a central axis in a vast cupola or dome 78 feet in diameter. The
Grand Equatorial of Gruenewald, at the recent Berlin Exposition, was
even still larger, since its object glass was 3 feet 7 inches, or nearly
2 inches larger than the Yerkes.
[Illustration: FIG. 195.--GREAT TELESCOPE, PARIS EXPOSITION. 1900.]
Even these great instruments have now been excelled in the Grande
Lunette, of the Paris Exposition, in 1900. When it is remembered that an
increase in the diameter of any circular body causes, for every
additional inch, a vastly disproportionate increase in the
cross-sectional area and weight, it will readily be seen how handicapped
the instrument maker is in any increase in the power of such a
telescope. An increased diameter of a few inches in the glass lens means
an enormous increase in the cross section, its weight and the
difficulties attending its successful casting free from imperfections,
and the perfect grinding and polishing of the lens. An increased length
of the tubular case of the telescope is liable to involve, from the
great weight, a slight bending or springing out of axial alignment when
supported near the middle for equatorial adjustment, and a few feet
increase in the diameter of the massive and movable steel dome add
greatly to the weight and incidental difficulties of constructing and
delicately adjusting it. The great Lunette, see Fig. 195, changes
entirely the method of manipulating the telescope, and also, in a
measure, its principle of action, so as to avoid some of these
difficulties. Its tube, instead of being pointed upwardly through the
slot of a movable dome, and made adjustable with the dome, is laid down
horizontally on a stationary base of supporting pillars, and an
adjustable reflecting mirror and regulating mechanism, called a
“siderostat,” is arranged at one end, to catch the view of the star, or
moon, and reflect it into the great tube, and through its lenses on to
the screen at the other end. The tube is 197 feet long, and the object
glass or lens is a fraction over 4 feet in diameter. There are two of
these, which together cost $120,000. The siderostat is supported on a
large cast iron frame, and is provided with clockwork and devices for
causing the mirror to follow the movement of the celestial object which
is being viewed. The entire weight of the siderostat and base is 99,000
pounds, the movable part weighs 33,000 pounds, and the mirror and its
cell weigh 14,740. The mirror itself is of glass, weighs 7,920 pounds,
is 6.56 feet in diameter, and 10.63 inches thick. To facilitate the
free and sensitive adjustment of this great mirror its base floats in a
reservoir of mercury. The entire cost of the instrument is said to be
over 2,000,000 francs. With the wonderful strides of improvement in all
fields of invention, it is not unreasonable to suppose that the
revelations in astronomy may keep pace with those of mundane interest,
and that great discoveries may be made in the near future. The average
individual does not bother himself much about the calculation of
eclipses, or the laws which govern the movements of an erratic comet. He
is, however, intensely personal and neighborly, and what he wants to
know is, Is Mars inhabited? and if so, are its denizens men, and may we
communicate with them? The wonderful regularity of the so-called canals,
of apparently intelligent design, already discovered on the surface of
Mars, has stimulated this neighborly curiosity into an expectant
interest, and who knows what marvelous introductions the modern
telescope may bring about?
[Illustration: FIG. 196.--PROF. ABBE’S STEREO-BINOCULAR.]
Many minor improvements have been made in recent years in the form of
the telescope known as field and opera glasses. Probably the most
important of these is the Stereo-Binocular, invented by Prof. Abbe, of
Germany, and patented by him in that country in 1893, and also in the
United States, June 22, 1897, No. 584,976. This gives a much increased
field, and also an increased stereoscopic effect, or conception of
relative distance, by having the object glasses wider apart than the
eyes of the observer. The field is also flatter, the instrument rendered
very much smaller and more compact, and no change of focus is required
for changing from near-by to remote objects. The rays of light, see Fig.
196, enter the object glasses, strike a double reflecting prism, and are
first thrown away from the observer, and then striking another double
reflecting prism, arranged after Porro’s method, are returned to the
observer in line with the eye-piece.
[Illustration: FIG. 197.--MODERN MICROSCOPE.]
_The Microscope._--Just as the telescope reveals the infinity of the
great world above and around us, so does the microscope reveal the
infinity of the little world around, about, and within us. Its origin,
like the telescope, is hidden in the dim distance of the past, but it is
believed to antedate the telescope. Probably the dewdrop on a leaf
constituted the first microscope. The magnifying power of glass balls
was known to the Chinese, Japanese, Assyrians and Egyptians, and a lens
made of rock crystal was found among the ruins of Ninevah. The
microscope is either single or compound. In the single the object is
viewed directly. In the compound two or more lenses are so arranged that
the image formed by one is magnified by the others, and viewed as if it
were the object itself. The single microscope cannot be claimed by any
inventor. The double or compound microscope was invented by Farncelli in
1624, and it was in that century that the first important applications
were made for scientific investigation. Most of the investigations were
made, however, by the single microscope, and the names of Borelli,
Malpighi, Lieberkuhn, Hooke, Leeuwenhoek, Swammerden, Lyonnet, Hewson
and Ellis were conspicuous as the fathers of microscopy. For more than
two hundred and fifty years the microscope has lent its magnifying aid
to the eye, and step by step it has been gradually improved. Joseph J.
Lister’s aplanatic foci and compound objective, in 1829, was a notable
improvement in the first part of the century, and this has been followed
up by contributions from various inventors, until the modern compound
microscope, Fig. 197, is a triumph of the optician’s art, and an
instrument of wonderful accuracy and power. Its greatest work belongs to
the Nineteenth Century.
Multiplying the dimensions of the smallest cells to more than a thousand
times their size, it has brought into range of vision an unseen world,
developed new sciences, and added immensely to the stores of human
knowledge. To the biologist and botanist it has yielded its revelations
in cell structure and growth; to the physician its diagnosis in urinary
and blood examinations; in histology and morbid secretions it is
invaluable; in geology its contribution to the knowledge of the physical
history of the world is of equal importance; while in the study of
bacteriology and disease germs it has so revolutionized our conception
of the laws of health and sanitation, and the conditions of life and
death, and is so intimately related to our well being, as to mark
probably the greatest era of progress and useful extension of knowledge
the world has ever known. In the useful arts, also, it figures in almost
every department; the jeweler, the engraver, the miner, the
agriculturalist, the chemical manufacturer, and the food inspector, all
make use of its magnifying powers.
To the microscope the art of photography has lent its valuable aid, so
that all the revelations of the microscope are susceptible of
preservation in permanent records, as photomicrographs. A curious, but
very practical, use of the microscope was made in the establishment of
the pigeon-post during the siege of Paris in 1870-71. Shut in from the
outside world, the resourceful Frenchmen photographed the news of the
day to such microscopic dimensions that a single pigeon could carry
50,000 messages, which weighed less than a gramme. These messages were
placed on delicate films, rolled up, and packed in quills. The pigeons
were sent out in balloons, and flying back to Paris from the outer
world, carried these messages back and forth, and the messages, when
reaching their destination, were enlarged to legible dimensions and
interpreted by the microscope. It is said that two and a half million
messages were in this way transmitted.
_The Spectroscope._--To the popular comprehension, the best definition
of any scientific instrument is to tell what it does. Few things,
however, so tax the credulity of the uninformed as a description of the
functions and possibilities of the spectroscope. To state that it tells
what kind of materials there are in the sun and stars, millions of miles
away, seems like an unwarranted attack upon one’s imagination, and yet
this is one of the things that the spectroscope does. A few commonplace
observations will help to explain its action. Every schoolboy has seen
the play of colors through a triangular prism of glass, as seen in Fig.
198, and the older generation remembers the old-fashioned candelabras,
which, with their brilliant pendants of cut glass cast beautiful colored
patches on the wall, and whose dancing beauties delighted the souls of
many a boy and girl of fifty years ago. This spread of color is called
the _spectrum_, and it is with the spectrum that the spectroscope has to
deal. The white light of the sun is composed of the seven colors: red,
orange, yellow, green, blue, indigo, and violet. When a sunbeam falls
upon a triangular prism of glass the beam is bent from its course at an
angle, and the different colors of its light are deflected at different
angles or degrees, and consequently, instead of appearing as white
light, the beam is spread out into a divergent wedge shape, that
separates the colors and produces what is called the spectrum. This
discovery was made by Sir Isaac Newton, in 1675.
[Illustration: FIG. 198.--PRISM AND SPECTRUM.]
In 1802 Dr. Wollaston, in repeating Newton’s experiments, admitted the
beam of light through a very narrow slit, instead of a round hole, and
noticed that the spectrum, as spread out in its colors, was not a
continuous shading from one color into another, but he found black lines
crossing the spectrum. These black lines were, in 1814, carefully mapped
by a German optician, named Fraunhofer, and were found by him to be 576
in number. The next step toward the spectroscope was made by Simms, an
optician, in 1830, who placed a lens in front of the prism so that the
slit was in the focus of the lens, and the light passing through the
slit first passed through the lens, and then through the prism. This
lens was called the “Collimating” lens. With these preliminary steps of
development, Prof. Kirchhoff began in 1859 his great work of mapping the
solar spectrum, and he, in connection with Prof. Bunsen, found several
thousand of the dark lines in the spectrum, and laid the foundation of
_spectrum-analysis_, or the determination of the nature of substances
from the spectra cast by them when in an incandescent state.
[Illustration: FIG. 199.--KIRCHHOFF’S FOUR-PRISM SPECTROSCOPE.]
The form of Kirchhoff’s spectroscope is given in Fig. 199. The slit
forming slide is seen on the far end of the tube A, and is shown in
enlarged detached view on the right. The collimating lens is contained
in the tube A. The beam of light entering the slit at the far end of the
tube A, passes through the lens in that tube, and then passes
successively through the four triangular prisms on the table, and is
successively bent by these and thrown in the form of a spectrum into the
telescopic tube B, and is seen by the eye at the remote end of said
tube B. The greater the number of prisms the wider is the dispersion of
the rays and the longer is the spectrum, and the more easily studied are
the peculiar lines which Wollaston and Fraunhofer found crossing it. It
was the presence of these black lines on the spectrum which led to the
development of the spectroscope and established its significance and
value. The work which the spectroscope does is simply to form an
extended spectrum, but this spectrum varies with the different kinds of
light admitted through the slit, the different kinds of light showing
different arrangement of colored bands and dark lines, and such a
definite relation between the light of various incandescing elementary
bodies and their spectra has been found to exist, that the casting of a
definite spectrum from the sun or stars indicates with certainty the
presence in the sun or stars of the incandescing element which produces
that spectrum. This application of the spectroscope is called
_spectrum-analysis_, and by rendering any substance incandescent in the
flame of a Bunsen burner, and directing the light of its incandescence
through the spectroscope, its spectrum gives the basis of intelligent
chemical identification. So delicate is its test that it has been
calculated by Profs. Kirchhoff and Bunsen that the eighteen-millionth
part of a grain of sodium may be detected.
The useful applications of the spectroscope are found principally in
astronomy and the chemical laboratory, but some industrial applications
have also been made of it in metallurgical operations, as, for instance,
in determining the progress of the Bessemer process of making steel, and
also for testing alloys. Many hitherto unknown metals have also been
discovered through the agency of the spectroscope, among which may be
named caesium, rubidium, thallium, and indium.
The field of optics is so large that many interesting branches can
receive only a casual mention. The polarization of light, first noticed
by Bartholinus in 1669, and by Huygens in 1678, in experiments in double
refraction with crystals of Iceland spar, were followed in the
Nineteenth Century by the discoveries of Malus, Arago, Fresnel,
Brewster, and Biot. Malus, in 1808, discovered polarization by
reflection from polished surfaces; Arago, in 1811, discovered colored
polarization; Nicol, in 1828, invented the prism named after him. The
Kaleidoscope was invented by Sir David Brewster in 1814, and British
patent No. 4,136 granted him July 10, 1817, for the same. The reflecting
stereoscope was invented by Wheatstone in 1838, and the lenticular form,
as now generally used, was invented by Sir David Brewster in the year
1849.
Among the more recent inventions of importance in optics may be
mentioned the Fiske range finder (Patent No. 418,510, December 31,
1889), for enabling a gunner to direct his cannon upon the target when
its distance is unknown, or even when obscured by fog or smoke. The
Beehler solarometer (Patent No. 533,340, January 29, 1895), is also an
important scientific invention, which has for its object to determine
the position, or the compass error, of a ship at sea when the horizon is
obscured. There is also in late years a great variety of entertaining
and instructive apparatus in photography, and improvements in the
stereopticon and magic lantern.
The most interesting of the latter is the Kinetoscope, for producing the
so-called moving pictures, in which the magic lantern and modern results
in the photographic art, have wrought wonders on the screen. The
old-fashioned magic lantern projections were interesting and instructive
object lessons, but modern invention has endowed the pictures with all
the atmosphere and naturalness of real living scenes, in which the
figures move and act, and the scenes change just as they do in real
life.
The foundation principle upon which these moving pictures exist is that
of persistence of vision. If a succession of views of the same object in
motion is made, with the moving object in each consecutive figure
changed just a little, and progressively so in a constantly advancing
attitude in a definite movement, and those different positions are
rapidly presented in sequence to the eye in detached views, the figures
appear to constantly move through the changing position. The theory of
the duration of visible impressions was taught by Leonardo da Vinci in
the fifteenth century, and practical advantage has been taken of the
same in a variety of old-fashioned toys, known as the phenakistoscope,
thaumatrope, zoetrope, stroboscope, rotascope, etc.
The phenakistoscope was invented by Dr. Roget, and improved by Plateau
in 1829, and also by Faraday. A circular disk, bearing a circular series
of figures is mounted on a handle to revolve. The figures following each
other show consecutively a gradual progression, or change in position.
The disk has radial slits around its periphery, and is held with its
figured face before a looking glass. When the reflection is viewed in
the looking glass through the slits, the figures rapidly passing in
succession before the slits appear to have the movements of life. The
thaumatrope, which originated with Sir John Herschel, consists of a thin
disc, bearing on opposite sides two associated objects, such as a bird
and a cage, or a horse and a man. This, when rotated about its diameter,
to bring alternately the bird and cage into view, appears to bring the
bird into the cage, or to put the rider on the horse’s back, as the case
may be. The zoetrope, described in the _Philosophical Magazine_,
January, 1834, employs the general principle of the phenakistoscope,
except that, instead of a disc before a looking glass, an upright
rotating drum or cylinder is employed, and has its figures on the
inside, and is viewed, when rotating, through a succession of vertical
slits in the drum.
The earliest patents found in this art are the British patent to Shaw,
No. 1,260, May 22, 1860; United States patents, Sellers, No. 31,357,
February 5, 1861, and Lincoln, No. 64,117, April 23, 1867. In Brown’s
patent, No. 93,594, August 10, 1869, the magic lantern was applied to
the moving pictures, and Muybridge’s photos of trotting horses in 1872,
followed by instantaneous photography, which enabled a great number of
views to be taken of moving objects in rapid succession, laid the
foundation for the modern art.
[Illustration: SHOOTING GLASS BALLS.
FIRING DISAPPEARING GUN.
FIG. 200.]
In Fig. 200 is shown a succession of instantaneous photographs of a
sportsman shooting a glass ball, and the firing of a disappearing gun. A
multiplicity of views extending through all the phases of these
movements, when successively presented in order, before a magic lantern
projecting apparatus, gives to the eye the striking semblance of real
movements. In practice these views are taken by special cameras, and are
printed on long transparent ribbons that contain many hundreds, and even
thousands of the views. Edison’s Kinetoscope is covered by patent No.
493,426, March 14, 1893, and his instrument known as the Vitascope, is
one of those used for projecting the views upon a screen. In Fig. 201 a
similar instrument, called the Biograph, is shown, in which the seeming
approach of the locomotive makes those who witness it shudder with the
apparent danger.
[Illustration: FIG. 201.--BIOGRAPH IN THE THEATRE.]
To secure the best results, the ribbon with its views should remain with
a figure the longest possible time between the light and the lens, and
the shifting to the next view should be as nearly instantaneous as
possible. This problem has been admirably solved by C. F. Jenkins, who,
in 1894, devised means for accomplishing it, and was one of the first,
if not the first, to successfully project the views on a large screen
adapted to public exhibitions. His apparatus is shown in Fig. 202. An
electric motor, seen on the left, drives, through a belt and pulley, a
countershaft, and also through a worm gear turns another shaft parallel
to the countershaft, and bearing a sprocket pulley, whose teeth
penetrate little marginal holes in the ribbon of views, and, drawing it
down from the reel above, deliver it to the receiving reel on the right.
On the end of the countershaft, just in front of the sprocket wheel, is
a revolving crank pin or spool, which intermittently beats down the
ribbon of views, causing the latter to advance through the vertical
guides in front of the lens by a succession of jerks. This holds each
view for a maximum period before the lens, and then suddenly jerks the
ribbon to bring the next view into position. In the Kinetoscope the
animated pictures not only present the movements of life, but, by a
combination with the phonograph, the audible speech, or music fitting
the occasion, is also presented at the same time, making a marvelous
simulation of real life to both the eye and the ear.
[Illustration: FIG. 202.--JENKINS’ PHANTASCOPE.]
Among the latest promises of the inventor is the “Distance Seer,” or
telectroscope, which, it is said, enables one to see at any distance
over electric wires, just as one may telegraph or telephone over them.
The surprises of the Nineteenth Century have been so many and so
astounding, and the principles of this invention are so far correct,
that it would be dogmatic to say that this hope may not be realized.
To the sum total of human knowledge no department of science has
contributed more than that of optics. With the telescope man has climbed
into the limitless space of the heavens, and ascertained the infinite
vastness of the universe. The flaming sun which warms and vitalizes the
world, is found more than ninety millions of miles away. The nearest
fixed stars visible to the naked eye are more than 200,000 times the
distance of the sun, and their light, traveling at the rate of 190,000
miles a second, requires more than three years to reach us. Although so
far away, their size, distance, and constitution have been ascertained,
and their movements are scheduled with such accuracy that the going and
coming thereof are brought to the exactness of a railroad time table.
The astronomer predicts an eclipse, and on the minute the spheres swing
into line, verifying, beyond all doubt, the correctness of the laws
predicated for their movements. The wonders of the telescope, the
microscope, and the spectroscope are, however, but suggestions of what
we may still expect, for science abundantly teaches that the eye may yet
see what to the eye is now invisible, and that light exists in what may
now seem darkness.
No man may say with certainty what thought was uppermost in Goethe’s
mind when, grappling in the final struggle with the King of Terrors, he
exclaimed “Mehr licht!” It may be that it was but the wish to dispel the
gathering gloom of his dimming senses, or perchance the unfolding of an
illuminated vision of a brighter threshold, but certain it is that no
words so voice the aspirations of an enlightened humanity as that one
cry of “More light!”