“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 31¹/₂ inches diameter, and focal length 17³/₄ 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, 37¹/₂ 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.

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[286]
[287] 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.

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?

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.

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.

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.

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.[296]
[297] 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.

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.

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.

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!”