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him, and by the payment of a considerable sum to procure a substitute in the militia, for which he had been drawn. At this time he was desirous of emigrating to the United States; but being unable to raise sufficient money to pay for his passage and outfit, he set himself steadily to work to repair his losses. In his leisure hours he studied mechanics and engineering, mended clocks and shoes, cut out clothes for the miners, and turned his hand to so many useful purposes that he was regarded by his fellow laborers in the colliery as a sort of universal genius. What was of more benefit to him was the favorable impression which his suggestions for improvements in machinery made upon his employers, who in 1812 appointed him engine-wright at Killingworth, at a salary of £100 a year. With this event his mechanical genius seemed to take a fresh start, and beside erecting a winding engine for drawing up coal and a pumping engine, he projected and laid down a self-acting incline along the declivity of the Willington ballast quay, so arranged that full wagons descending to the vessels drew up the empty ones. The construction of an efficient and economical locomotive steam engine, however, occupied his attention beyond any other subject; and after a careful examination of all the machines within his reach, he commenced, and in July, 1814, completed an engine, which worked successfully on the Killingworth railway, and proved the best yet constructed, though its operation was by no means satisfactory to the inventor. It was the first locomotive made with smooth wheels, and from the outset he rejected the clumsy contrivances which Trevethick, Blenkinsop, and others had thought necessary to secure sufficient adhesion between the wheels and the smooth iron surface of the rails to allow the propulsion of a train. At this early day also he told his friends "there was no limit to the speed of such an engine, if the works could be made to stand it;" an opinion he was subsequently obliged to maintain almost single-handed against the most experienced engineers of England. While engaged in plans for an improved engine, his attention was attracted to the increase in the draught of the furnace obtained by turning the waste steam up the chimney-a practice originating solely in the desire to lessen the noise caused by the escape of the steam; and it immediately occurred to him that the proper application of this principle, by increasing the force of the fire, would greatly augment the power of the boiler to generate steam, and the range and capacity of the engine. Hence originated the steam blast, the most important improvement in the locomotive made up to that time, which, however, has also been claimed for Hackworth, another inventor. It was embodied in Stephenson's next engine, completed in 1815; and in 1816 he constructed others, greatly simplified in the working parts, and which as recently as 1854 formed the model for those employed at

Killingworth to drag coal. About this period he invented a miner's safety lamp to obviate the frequent explosions from fire damp, one of which had occurred in 1814 in the colliery under his care. The subject was at the same time brought under the notice of Sir Humphry Davy, and both he and Stephenson, though living hundreds of miles apart, and personally unknown to each other, constructed lamps founded upon identical principles, but arrived at independently by different trains of thought, the former working out his ideas scientifically, the latter mechanically. Stephenson's lamp was practically tested by himself at Killingworth in Oct. 1815, nearly 3 weeks before Sir Humphry made public his invention, and is still employed there. To Davy nevertheless was ascribed the priority of invention, and a sum of £2,000 was raised at a meeting of coal miners and presented to him, £100 being at the same time assigned to Stephenson. The friends of the latter, deeming that injustice had been done him, soon after presented him with £1,000, a proceeding warmly criticized by Sir Humphry, and which provoked a bitter controversy between the partisans of the rival claimants. Having brought the locomotive to a considerable degree of perfection, Stephenson next turned his attention to the improvement of railways, his opinion being that both were parts of one mechanism, and that the employment of steam carriages on common roads was impracticable. For the purpose of making his railways solid and level, and to prevent jerks at the junction of the rails, he took out in 1816 a patent for an improved rail and chair, recommended the employment of heavier rails and the substitution of wrought for cast iron, and established the gauge still generally in use. In connection with these improvements he added considerably to the lightness and strength of the locomotive, and substituted steel springs for the small cylinders on which the boiler had at first rested. Soon after the general peace of 1815 the necessities of internal commerce began to suggest the establishment of railways, although the employment of steam power, except for the purpose of expediting the ascent of heavy grades, was generally considered impracticable. Stephenson and a few others, however, ventured to believe that the locomotive was destined to supersede the mail coach, and the railroad to "become the great highway for the king and all his subjects." His first important undertaking was the construction of a railroad 8 miles in length for the owners of the Hetton colliery, which, on Nov. 18, 1822, was successfully opened, the level parts being traversed by locomotives, while stationary engines were employed to overcome the heavy grades. While this work was in progress similar projects began to be agitated, and in 1820 an act of parliament was obtained for a railway between Stockton and Darlington, of which Stephenson was appointed engineer at a salary of £300. The line was intended to be worked by station

ary engines for the steep gradients, with horse power on the level portions; but at Stephenson's urgent request the act was amended so as to permit the use of locomotives on all parts of the road, which, at the expiration of some. what more than 3 years from its commencement, was formally opened on Sept. 25, 1825, in the presence of immense throngs of spectators. The difficulty experienced in procuring suitable locomotives from the ordinary blacksmiths' shops suggested to him the necessity of establishing a special engine factory, which project was successfully carried into effect, with the cooperation of Mr. Pease, the originator of the Stockton road, at Newcastleupon-Tyne, where some of the most powerful steam carriages in the world have since been constructed, and many skilled workmen and engineers educated. The year 1825 witnessed the production of a multitude of projects for railways, of which the Liverpool and Manchester line, the most considerable and the only one seriously supported, was destined to be not merely the great achievement of Stephenson's career, but the battle field on which were to be fought the momentous questions of the superiority of railways to common roads, of high to low velocities of transport, and of locomotives to fixed engines. Stephenson made the preliminary surveys in the teeth of an opposition which might have readily disconcerted a less determined spirit; and such were the ignorance and prejudice of land owners and their agents, who sometimes drove the surveyors off their grounds, that much of the work had to be done by stealth. An act of parliament having been procured, Stephenson was appointed principal engineer, and in June, 1826, commenced the construction of the road, which employed him incessantly during the next 4 years. Of the engineering difficulties successfully overcome, the most important was the crossing of Chatmoss, a bog 4 miles in length, pronounced impassable, on which the road was made to float; a feat, as has been observed, "affording an unequivocal proof of that admirable self-reliance which never contemplates failure." The patience of Stephenson was however destined to be still more severely tried; for during the progress of the undertaking the most eminent engineers persisted in recommending stationary engines in place of locomotives, which they declared unsafe and incapable of attaining a high degree of speed; and the clumsy expedient of a series of stationary machines 11⁄2 miles apart, dragging the trains by ropes, was seriously entertained, and would have been adopted but for the energy of Stephenson and a few of his friends. He finally prevailed on the directors to offer a prize, under certain stipulations, for the most effective locomotive engine for the purposes of the road; and at a trial which took place near Liverpool, Oct. 6, 1829, his engine, the "Rocket," constructed by himself and his son Robert, was adjudged to be the best of the 4

entered, having averaged a speed of 14 miles an hour, and even attained a velocity of 29 miles an hour. The "Rocket," the first highspeed locomotive of the standard modern type, was distinguished above all preceding ones by 3 elements of efficiency: the multitubular boiler, which, if not Stephenson's invention, was first applied by him to locomotives; the blast pipe; and the direct connection of the steam cylinders to one axle and one pair of wheels. At the ceremony of the opening of the road, Sept. 15, 1880, Mr. Huskisson, who was in attendance with many other distinguished public men, having been accidentally struck down and fatally injured by this engine, was conveyed in it from Parkside to Eccles, a distance of 15 miles, at the then unprecedented rate of 36 miles an hour. Having fairly inaugurated the railway system of England, Stephenson was almost incessantly employed for the next 10 years on new roads which were projected in all directions, and even visited Belgium and Spain as a consulting engineer. With his increasing wealth he also engaged extensively and profitably in coal mining, particularly in the neighborhood of Tapton park, an elegant seat in Derbyshire, where he passed his latter years in comfort and peace, beloved by his neighbors of every degree and condition, and presenting in his conduct, as well as in his person and manners, the true ideal of an English gentleman. He preserved through life the simplicity of character which had distinguished him in youth, and on several occasions declined the honor of knighthood. Of his. scientific character, Sir J. D. Forbes, who disclaims for him any great inventiveness, makes the following estimate: "His skill rather lay in perceiving how far methods and contrivances already known might be pushed to an advantageous result. He possessed that shrewd decision which ingenious persons often want, enabling him to detect what is truly valuable in the numerous mechanical schemes which at any time are afloat, and to devise the means of realizing them. He also possessed that confidence in his own judgment which is necessary to carry out principles to their legitimate extent, but from which feebler or more practical minds usually shrink." A memoir of George Stephenson, by Samuel Smiles, was published in London in 1856.—ROBERT, a railway constructor and engineer, son of the preceding, born in Willington, near Newcastle-uponTyne, Dec. 16, 1803, died Oct. 12, 1859. As a child he evinced remarkable intelligence, and became in some sort a fellow pupil in several branches of knowledge with his father, whose own education was continued far into middle life, and whose earnings were long devoted exclusively to the instruction of his son. The latter, who at 12 years of age began to show a decided inclination for mechanics and science, was, after several years' schooling at Newcastle, and a preparatory training in the collieries, sent in 1822 to the university of Edinburgh.

He returned home in the succeeding year, and after assisting his father in a variety of undertakings and perfecting his knowledge of practical mechanics, accepted in 1824, in the hope of benefiting his health, an engagement as mining engineer in South America. Recalled by his father in 1827, he was employed in various labors connected with the construction of the Liverpool and Manchester railway, and in the improvement of locomotives; and in 1829 he assisted in designing and making the successful locomotive, the "Rocket," which was entered in his name. After being engaged on several minor railway lines, he was appointed engineer of the London and Birmingham road, which under his direction was completed in 1838; and thenceforth for many years his time and talents were almost exclusively occupied with similar undertakings at home and abroad. As an engineer he is known by several stupendous works designed in immediate connection with railways, among the most remarkable of which are the high level bridge over the Tyne at Newcastle, the viaduct over the Tweed valley at Berwick, the Conway bridge, and above all the Britannia tubular bridge across the Menai straits, 1,850 feet in length and 106 above high water mark, which Sir James Forbes pronounces 66 a triumph of art and science, an honor to his own age, and a lesson to posterity." In this last undertaking he received important assistance from Messrs. Hodgkinson and Fairbairn with respect to various points of construction and the strength of materials; but the credit of conceiving the enterprise belongs wholly to himself, as well as the rectangular form of the tube, of which there had previously been no example in mechanical construction. He was also employed on railways in Belgium, Norway, Italy, France, and other parts of Europe, and visited Egypt several times to superintend the construction of a road between Alexandria and Cairo, on the line of which there are two tubular bridges, traversed by trains on the roof instead of the inside, as in the case of the Britannia bridge. He also designed an immense bridge across the Nile at Kaffre Azzayat. In British North America he has left a memorable specimen of his engineering skill and perseverance amid unprecedented difficulties in the great Victoria tubular bridge, which crosses the St. Lawrence near Montreal, and was formally opened by the prince of Wales in the summer of 1860. In addition to his railway labors he took considerable interest in public affairs, and during the last 12 years of his life represented the Yorkshire borough of Whitby in parliament, where he was known as an able debater on subjects connected with the railway interests of the United Kingdom. He was also a member of several scientific bodies, and received a great gold medal of honor from the French industrial exposition of 1855. His great wealth was liberally expended, and he enjoyed a reputation for private worth and mechanical ge

nius not less distinguished than that of his father. He published a work "On the Locomotive Steam Engine," and another "On the Atmospheric Railway System."


STEREOSCOPE (Gr. σTEрeos, solid, and σкоже, to see), an optical instrument contrived for combining into one image, which appears solid, or in relief, two plane representations of a statue, a landscape, or any object or field of objects involving three dimensions. The two separate pictures employed for this purpose are so taken as to show the object or field as it would appear when viewed by each of the two eyes separately. Of such pictures, now known as stereoscopic views, the effect, and hence the preparation, depend on the two simple principles, that within certain limits of distance the two eyes see at the same time two really unlike pictures of any solid object or field of objects regarded; and that when two such pictures (for present purposes considered as flat) fall on the retina of the corresponding eyes, the result is a perception of solidity in the objects, or of depth in the field, so presented. If a thin book be held up before the eyes, with the back toward the face, and looked at with the right eye only, the back and much of the corresponding side are seen, and in a certain direction; but on looking with the left eye only, the image of the book and the plane in which it appears to lie shift slightly toward the closed eye, and the back with the other side now becomes visible. The book presents to each eye a somewhat different surface, and a different position and perspective. On carefully regarding it with both eyes, its apparent position is intermediate to the two before found; the back and in a degree both the sides are now visible, and the book obviously stands in relief toward the eyes. These appearances, alluded to by Euclid, were more definitely observed and described by Galen about 1,700 years since. The familiar but remarkable result is, that we neither see objects double nor as flat surfaces; but always, when not too far removed, as having depth or relief, or as existing in a space which shows this third dimension. (See VISION.) A diagram expressing to the eye Galen's results was drawn by Baptista Porta; and from this, about A. D. 1593, Jacopo Chimenti prepared pairs of drawings (one pair of which is believed to be still preserved in a museum at Lille) intended to show persons as seen by the two eyes separately, and such that, if viewed with the eyes "crossed" by looking at a point nearer to them than are the drawings, so that each eye receives the image of that which is before the other, they are combined, giving a single image in relief. This method, the "ocular stereoscope," is still conveniently resorted to, after some practice, by those who would get the stereoscopic effect of views without employing an instrument. Aquilonius (1613) wrote a volume on the vision of solid objects,

in which this principle was introduced. Mr. Harris (1775) treated on the subject, among other things referring the obviously solid form of the nose as seen by its owner to this effect of vision with two eyes. Prof. Elliott, in 1834, is said to have conceived the plan of an instrument for combining the two single-eye pictures, mentioning it to two or three friends, but not carrying it into execution until 1839. Meanwhile, however, Prof. Wheatstone-to whom is unquestionably due the credit of having devised the first effectual and satisfactory instrument for combining two monocular drawings or pictures into a solid image, as well as of having distinctly brought before the physicists and the public the truth that our actual perception of solidity depends on the combination of two such visual pictures-had exhibited before the royal society in 1838, and also at a meeting of the British association, his "reflecting stereoscope," demonstrating its power to unite pairs of plane geometrical drawings into single and solid forms. Elliott's device was simply a wooden box, 18 inches long, 7 broad, and 4 deep, in the closed or remote end of which the dissimilar pictures were placed. The views he first employed were two representing a leaning cross, with the moon and the branchless stem of a small tree, nearly in line, and as seen from slightly different positions. No mirrors or lenses are required; but on looking into the box, on the "ocular stereoscope" plan, crossing the eyes, the entire view appears to stand forth in solidity or relief. Wheatstone's arrangement, far superior to this, consists of two plane mirrors about 4 inches square, so placed as to make each an angle of about 45° with the axis of the corresponding eye, the two mirrors being thus at right angles to each other, and the drawings on separate slips being presented, each toward a mirror, at the two sides, and at such a distance and angle that the reflected images thrown to the two eyes respectively shall appear to have come from a single object at a corresponding distance behind the mirrors. Thus the two views are in effect superimposed and united, as in natural vision; and if unlike each other in quite or nearly the same way as when received by the eyes from the actual object, the latter will be exactly represented, though it may be on a reduced scale, but appearing in solid form, so that we seem even to look around and beyond it. Two pictures of a bust become in effect a solid bust; the waters of a cataract stand forth in body; a forest, a mountain, or a group of persons comes out in depth, and we look between and beyond the individual objects, as in the natural view. In 1849 Sir David Brewster devised a more convenient form of instrument for combining the two pictures, which is now in common use. In this, two convex lenses properly adjusted are employed for viewing the pictures; or more commonly, parts of a single large double-convex lens, divided in the middle, the thin edges being set

toward each other, and at the ordinary distance of the two eyes, about 2 inches apart. These are placed in a convenient box, into which the observer looks; while beyond them are the slides or double views, which, in case they are opaque, as upon pasteboard, are viewed by reflected, or if transparent, as on glass, by transmitted light. A diaphragm, extending from in front between and to a little way beyond the two semi-lenses, confines the vision of each eye to its appropriate picture; while the lenses, refracting laterally outward to the eyes the light which passes through them, cause the two images to appear as if originating from a single field between the real places of the views, that is, they superimpose these; and at the same time their effect is to magnify the single resulting image. The instrument is known as the "lenticular stereoscope.' In the best simple or hand instruments, the semi-lenses being cut from a single lens not less than 3 inches in diameter, and set edge to edge, a single wide aperture serves for both eyes; and the instrument then suits all eyes without adjustment, and allows of an increased field of view.-As no artist can continually and with certainty execute true pictures of trees, persons, or other near objects, with just those differences of surface and perspective which they naturally present to the two eyes separately, it will readily be seen that the stereoscope could be of little use until aided by photography. The pictures employed must be correct, or their faults are exaggerated. Public attention seems first to have been strongly called to the stereoscope as a means of amusement and of the improved representation of objects, by the fine display of lenticular stereoscopes and of appropriate photographic views placed by M. Duboscq in the great exhibition at London in 1851.-It is certain that the perception of solidity or relief, in ordinary vision, is in some way connected with the degree of convergence of the axes of the two eyes (the optic axes) toward the object, or the point on its surface of which at any moment distinct vision is secured. Though we usually judge of distances in a considerable degree, and beyond a certain limit wholly, by light and shade, or aerial perspective, by intervening objects, and by aid of experience, yet when the objects or their parts are within about 250 to 300 feet, there is a sensible difference in the degree of convergency of the optic axes, and hence in the effort to fix the eyeballs in the required positions, and doubtless therefore in the attending muscular sensations. Within some limit, probably that named, the degree and character of these sensations, though unconsciously to him, enable the observer to judge of distances; to determine that some parts of a given object are nearer, others more remote; and thus, perhaps, during the rapid play of the eyes over the object, to obtain that sense of distances which we interpret into solidity of the object. For objects about 250 feet away, the optic an

gle is small, and the sensation of effort slight; for those much beyond this, both these in effect vanish, and relief is no longer a perception, but only an inference; for distances far within the limit, the convergency and sensation become marked. Looking into the stereoscope, the effort to converge the eyes must be made, the sensation of such effort attends, and relief is perceived. It may be in this way that two views of an object a mile distant, and taken by the double camera in common use, its lenses little further apart than the eyes, still show relief when seen in the instrument; and that, as has been stated, even two flat pictures exactly alike have in the instrument been made to afford a view in relief. Brewster argues that to produce perfect stereoscopic effect, the two views should always be taken through lenses of the double photographic camera, having no more than inch diameter, and placed no more than 2 inches apart, or successively through one such lens shifted only to such distance, so as to answer exactly to the pictures furnished in nature to the two eyes. When there are moving objects in the field, and also in taking "instantaneous views," so called, the double camera becomes requisite, or two single cameras, stationed at suitable distance and acting together. For stationary objects the single camera is conveniently used, the pictures being taken in succession. In taking stereoscopic pictures, it has been customary (though probably the tendency is now back toward the natural conditions) to exaggerate the effect both in respect to distance between stations and to the size of lens. When the plates used are less sensitive, larger lenses may be employed to accelerate the process; sometimes those of 2, 3, or 4 inches diameter. So a broad base or distance between stations of the camera is resorted to for the purpose of exaggerating the relief; for near persons or statues, sometimes as much as 6 to 8 inches; for landscapes, 10 to 20 inches, or even several feet. Thus, strongly differing sides, perspectives, or projections of the objects are obtained. In the double camera, the tubes through which light enters, to be thrown by a convex lens in each on the prepared plates, are not parallel, but inclined to each other at a certain angle, which is usually less in the cameras for taking portraits than in those for views. But in taking the photographic visiting cards, by 4 parallel tubes directed toward the person and view at the same time, 4 pictures are obtained; then, without shifting the person or instrument, 4 others upon another portion of the same slide; and it is unexpectedly found that of these, any right-hand image being suitably placed in the stereoscope with any left-hand image, perfect relief is the result. With near objects, a long base line and marked difference of perspective result in distorting the objects in the direction from before backward (that of depth); all streets, buildings, and similar views extending away from the eye, appear disproportionately long; and in

persons, the head, or an advanced foot, or the dress, is thrown forward to a disagreeable extent. This principle, however, becomes useful in case of bodies so distant that to the eyes, near together as they are, they cannot present the solid form. Remote mountains, buildings, &c., flat to ordinary vision, are made to give unlike views by placing the cameras many feet apart, as they would to a person whose visual organs could be correspondingly separated; and in the stereoscope such views actually give the solid form. This is also the principle of the tele-stereoscope of Helmholtz, in which 4 mirrors are so placed diagonally, the outer pair many feet apart, and the inner at the distance suiting the eyes, that the binocular parallax or angle between the two lines of sight is greatly enlarged, and distinct relief is secured in objects very remote. The angle made by the axes of the two eyes at the point viewed (the "optic angle") is, by both the two methods last named, in effect greatly enlarged-this angle being always a horizontal one-as if the object were very near; but the visual angle of the object, usually regarded especially in the vertical direction, remaining just what it would be with the ordinary base between the eyes, the result is that the judgment of the observer is deceived, and, unless proportionate magnifying power of lenses be employed, the object appears actually diminished in size. The principle of increased distance between stations is availed of in taking stereoscopes of the moon, as has been done by L. M. Rutherfurd of New York, and by W. De la Rue of London. At different seasons the moon presents slightly different faces toward the earth; and two views taken from positions in the earth's orbit 15° apart, and placed in the stereoscope, give a perfect and beautiful globe, its surface diversified with the well known lights and shades of that luminary, M. Claudet, of London, has devised a method in which relief is secured by means of the image of a single picture or object thrown on a ground glass screen, hence termed a stereomonoscope. In this case it is asserted that the image in relief is visible to several spectators at the same time. Another method, by Mr. Maugham, applies glasses of complementary colors, say green and red, to the rays which are thrown by a magic lantern on the screen, and corresponding glasses to the two eyes of each observer, in order to keep separate the rays of the two images; but much light is in this way lost, and the image is faint. Mr. Thomas Skaife, of Blackheath, England, using a small thin lens, of 1 inch focus, has obtained almost instantaneous views which, when magnified, are still extremely well defined and perfect, and which he has termed pistolographs. Enclosed between two plates of glass, and the three semi-fused into one, one of these miniature pictures retains its beauty, while it is protected and preserved; the combination he has termed the chromo-crystal. It is stated that Mr. John Sang, of Kirkcaldy, has recently, by

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