Casting a Great Lens

Ray Stannard Baker

McClure’s/October, 1900

A New Venture in Practical Philosophy

It had just turned afternoon in the furnace house of the glass works of Jena. For upward of two hours everything had been in readiness for the casting of the great lens, everything except the glass. The Master had directed the placing of the huge circular iron mold near the open doorway and just between the two furnaces—the one from which now burst the fervid white radiance of the molten glass, and the one in which through weeks of lessening heat the lens, when cast, was to be cooled and toughened and tempered. The mold was a meter and a quarter in diameter—over four feet—and the lens here to be cast would make one of the largest in the world, large enough to bring the moon within a few score of miles of the earth, and one so perfect, perhaps, as to surprise new secrets from the sun itself.

The Master had sprinkled the bottom of the mold with fine sand from a curious tin pot, that the hot glass might not take up impurities from the iron. A dozen brawny workmen, in blue blouses and wooden-soled shoes, had come in to man the long, wheel-mounted tongs which were to drag the crucible from the furnace bed. Other workmen with sledges and bars had torn a gaping hole in the front of the cooling furnace, so that it would be ready for the instant admission of the lens.

So everything was ready. The Master, shading his face with his upraised arm, peered into the  glory” hole of the melting furnace, as he had been doing with ever greater frequency for hours past. He watched for a moment the shimmering, wrinkled surface of the molten glass within the crucible, and then he followed the movements of the stirring lever. Was the color exactly right? Did the sluggish waves which followed the stirring plunger show thick or thin enough?

At last the time came. The Master gave the word, and a dozen men sprang forward with hooks and bars. The “glory” hole was hardly larger than a man’s head—just sufficient for the passage of the stirring lever and to permit examination. With this as a beginning, the workmen tore out the whole front of the furnace, working with the utmost activity, their heelless shoes clattering on the stone floor as they rushed back and forth. The stirring lever was dismantled, and the stirring plunger itself, white-hot and sparkling with the dust that fell upon it, was cast outside, where it lay, a deep wine-red, in the sunshine.

The grappling tongs were thick bars of steel about thirty feet long, mounted on iron wheels. As soon as the furnace was open, the grappling ends were thrust inside, one on each side of the crucible, the men at the other end leaning back with heads averted to avoid the fervid outburst of heat.

Although the novice could not see it because of the brightness of the glow, there was a thick ridge around the crucible, about halfway up. Under this the tongs fitted themselves. The men at the other end bore down hard, but the crucible did not stir. It was firmly fastened to the furnace floor by the glass that had spilled in the melting. It was an anxious moment. Crucibles have been broken in lifting. The Master raised his hand. Slowly the men added their weight at the far end of the lever. The crucible broke suddenly free, jogging a little, so that a bit of the glass overflowed and ran down like thick syrup. An instant later the crucible was outside the furnace, filling the whole of the high dim room with heat and light, like a new sun. And thus it was pushed down the room toward the mold, a thing of exquisite beauty, and yet of terror, showing a hundred evanescent colors, changing red, pink, yellow, violet.

The crucible was lowered to the floor, the tongs were removed, and a workman cast a beard of asbestos over the glass to prevent too rapid cooling. Here it stood a few minutes, and when the crucible began to define itself, one discovered that it was made of fine yellow-glazed pottery. Imperfections on its surface stood out like specks on a mirror, or as one would imagine the spots on the sun.

It had required long hours for a man to fashion the clay of this crucible, and many weeks for it to dry, and then for days before it was used it had been slowly heated to prepare it for the high temperature of the furnace. And with this single melting its service is finished and it is consigned to the scrap heap.

Three men with thickly gloved hands are now fastening an iron band around the crucible just under the ridge. On each side of this band there is a protruding pivot of steel which fits into a socket in the ends of the grappling tongs, thus permitting the crucible to be tipped up as if on an axle. Again the men rest their weight on the other end of the tongs, the crucible is lifted, and an instant later it is poised over the iron mold. The critical point of all this labor has at last been reached. There is a pause as if the workmen felt the anxiety of the moment. The foreman, with his hand on the tilting lever, awaits the Master’s word. There is a shout, a quick upward swing of the foreman’s arm, and out from the crucible slips the molten glass. It has been a moment of so much stress that one anticipates a crash as the glass touches the cool iron of the mold, but there is absolute silence—not so much as a hiss or the sound of the splash. There is something indescribable about the fluidity of this mass. It seems thick, like oil, and yet it spreads more swiftly than water: it is more like quicksilver than anything else that one can think of, and yet not at all like quicksilver.

The mold, with the glowing lens inside, was now covered with a plate of iron, wheeled to the mouth of the cooling furnace, and lifted with chain tackle to the height of the furnace floor. A movable-frame tramway was then placed underneath it, and it was quickly pushed into the furnace. Workmen were ready with brick and mortar, and in ten minutes the lens was walled in. Here it is cooled for two weeks, and then brought again to the open air, dull and milky of surface and possessing only the general shape of a lens. After that, for days and weeks, workmen are employed in polishing it, not to give it the final form which it will have in the great telescope, but merely to prepare it for that important and anxious day when it will be submitted to those searching tests for imperfection, during which it must pass even the close scrutiny of microscopic and spectroscopic examination. A few bubbles it may have and pass, for bubbles have no effect, except to reduce the passage of light in a minute degree; but veins, denoting the improper mixture of the ingredients of the glass, it must not have. If it passes all the tests—and sometimes it requires many castings and costs many rejected lenses of this most precious of glass before the necessary perfection is attained—it is again sent to the furnace house, where with even greater care than before it is slowly raised to a high temperature, and thus annealed, and then as slowly cooled for two months or more. After that it is ready for the lens-maker proper, that skilled mechanician and mathematician of Jena or of America or of France, who polishes down its sides with infinite care, until they reach the most perfect curves appropriate to the refraction and dispersion of the glass disks employed. Each of these processes has absorbed precious time and has cost much money: the bare glass for such a lens would cost about $5,000. To this the skill of the optician would add in polishing perhaps $20,000 more, so that the finished lens, ready for fitting into the telescope tube, would represent an expenditure of some $25,000. Through such pains and expense as this must science pass that mankind may add a few facts to its knowledge of some distant star.

The German workmen are standing back from the cooling furnace, perspiring, the lens finally cast. A boy comes in with his apron full of beer, a bottle for each, and they drink in characteristic German fashion to the success of the work. It may be many a day before such another lens is cast.

The quaint old city of Jena in the German Grand Duchy of Saxe-Weimar is chiefly famous for three things. It has an unfading claim on history because Napoleon once marched through its streets and won a celebrated victory on the hills to the north—the battle of Jena—and in the present it is known the world over for its university and for its glass and lenses. There are glass works, if not lens manufactories, of far greater extent in America and in other parts of the world than these of Jena, and yet Jena glass and Jena lenses have their own unique claims to distinction, especially among men of science.

Not only in their processes of manufacture and in the perfection of their products are these works famous, but the management of their business affairs furnishes a most unique and fascinating study in social economy, for here the dream of an idealist has been given unique and wonderfully practical application, with the result that the workingmen of Jena have opportunities and rewards unequalled, perhaps, anywhere else in the world. And curiously enough, owing to the modesty of the originator of this scheme for the elevation of the workingmen and for the advancement of science, very little has ever been published about it, and nothing in English so far as I can learn. With German conservatism. Professor Abbe has desired to give his experiment the test of years before recommending it by a formally published account.

For many reasons it is not probable that such institutions as these—for in reality they partake as much of the character of public institutions as of regular business enterprises—could have originated in America. They would seem to be a product typically German, a result in part of what may be called the German scientific temperament, and in part of the wave of commercial expansion now sweeping over Germany. Many years ago Professor Abbe, who then, as now, filled the chair of applied mathematics, natural philosophy, and astronomy in the University of Jena, became deeply interested in lenses and lens-making. He had seen the defects of the lenses in use for astronomical and microscopical work, and he set himself to establish by purely mathematical calculation the exact curves at which lenses would give the greatest possible effect with regard to the refraction and dispersion of the light which passed through them. In other words, he sought to form a new and scientific theory for making lenses. He then interested himself in the modest lens works of Carl Zeiss, of Jena, and here he had lenses made according to exact scientific methods. Before his time lens-making was largely a matter of experience and experiment on the part of highly skilled workmen. Professor Abbe succeeded in laying down exact mathematical formulae.

But it was not long before he discovered that a complete revolution in glass-making was necessary in order to accomplish the great results at which he was aiming. The task seemed to be insurmountable, but it did not daunt him. His first step was to interest Dr. Schott, of Witten, in the work. Dr. Schott was not only a thorough scientist, especially in chemistry, but he possessed a technical knowledge of glass-making, as it was then conducted. In 1881 the first smelting experiments were made in a small laboratory erected in Jena for that purpose. There was a deliberate plan on the part of the two scientists to solve by scientific methods the difficult problems of glass-making, though they involved not only the most advanced optical research, but the most difficult chemical and technical manipulations.

Almost at once they began to get promising results, and after two years they were prepared to carry on their experiments on a larger scale, but this they did not have the means to do. In America or in England the work might have failed just at this point, but in Germany help came as help rarely comes outside of Germany. Professor Abbe laid his results before the Prussian government, showed what had been done, and what needed to be done, and the wide-reaching effect which favorable results might have in every department of science—the possibility of making microscopes, telescopes, and photographic lenses of hitherto unequaled definition and power, and of producing thermometer and barometer glass which might advance the science of temperature and pressure determination. The government at once felt the commercial appeal. Germany must needs buy all of her glass for scientific purposes in Paris or in Manchester, and here was an opportunity for building up a new industry which would employ German workmen and bring money into Germany. So the Prussian Government appropriated 30,000 marks ($7,500) in 1883, and the same amount in 1884, to have the experiments carried forward. At the end of that time, so successful were the investigators that a regular glass-making establishment was well under way, and there was no further need of governmental assistance. In four years’ time these glass works furnished a large proportion of the fine scientific and optical glass used in Germany, and now their wares are known everywhere in the world—in the form of microscope and photographic lenses and prisms, of thermometers, of chemical apparatus, and of the highest grades of commercial glass. This little story is especially interesting as showing why Germany is making such extraordinary strides in commercial affairs. Out of science, assisted by the state, has sprung a new and profitable industry.

In all, over one hundred new kinds of glass were originated and are now manufactured at the Jena glass works. In former times glass was composed almost entirely of the silicates, potassium, lead, soda, and lime, and there were, roughly speaking, only two varieties: the old-fashioned standard crown glass and flint glass. Professor Abbe and Dr. Schott used no fewer than twenty-eight new substances in glass-making: phosphorus, borax, magnesium, zinc, cadmium, bismuth, iron, mercury, antimony, tin, and others. Each of these substances has its own peculiar effect in the refraction and dispersion of light, and in doing away with or lessening what is known as the secondary spectrum. Much of the glass thus produced has been ground into lenses at the Carl Zeiss Works, and the resulting microscopes give a new impetus to every department of science which has to do with minute forms of matter or of life. It would have been impossible for Dr. Koch and other great contemporary investigators in bacteriology, for instance, to have made the astonishing additions to our knowledge of the life of microbes and bacteria had not Professor Abbe first produced a perfect or nearly perfect instrument for examining those low forms of life. In all of his published reports Dr. Koch as well as other scientists give Professor Abbe a large share of the credit for these profoundly important discoveries in connection with the germ theory. In the same way the Jena microscopes have done wonders in the hands of such men as Haeckel in laying bare the wonderful life processes of the lowest forms of plant and animal existence, in tracing the development of each, and in forming the great chain of proof of the theory of evolution. In the same way our present minute knowledge of embryology and the growing mastery of the details of that marvelous machine, the human body, are due to the efforts of that modest, hard-working professor of Jena.

The achievement of the investigators lay not so much in producing microscope and telescope lenses of higher magnifying power—that service science did not need—but in so perfecting the lenses that the image would be clear and clean-cut, or, in the words of the science, “in securing perfect definition.” A microscope which magnifies 4,000 times and produces such a blurred image of a cell that the investigator cannot tell whether or not it contains a nucleus, is not as valuable to science as one that magnifies 500 times and brings out every minute detail distinctly and sharply. And that is also just the distinction between a good and a poor photographic or telescope lens. Professor Abbe also introduced the system of “oil immersion” and other great microscope improvements. Indeed, he may be justly called “the father of the modern microscope.”

From the investigations thus begun in a laboratory by Professor Abbe and Dr. Schott have sprung two great manufacturing plants, separate and yet allied, neither of which is able to keep up with the present demand for its product. We visited the Schott Works on the hill above Jena, where all the new varieties of glass are made, and afterwards at the Carl Zeiss Optical Works we saw this glass ground and polished with infinite care and precision into lenses and prisms.

In the manufacture of optical glass for the microscope lenses—I have already described the processes of making a great telescope lens—the constituents of the glass are mixed with great care under the supervision of expert chemists, then the heating and stirring goes forward for several days, until the glass is hardly thicker than water and thoroughly mixed. After that it is taken from the furnace and allowed to cool in the crucible. Of course it cracks into hundreds of pieces, some large and some small. These pieces are carefully assorted, and all the imperfections chipped off—we saw two men, their eyes protected by goggles, employed with hammers at this work. It is interesting, and significant of the care required in these processes, that in spite of experience and the closest attention, more than one-fifth of all the glass melted is regularly rejected owing to imperfections. These pieces of glass are now placed in a square clay mold or chamotte of just the size that the future rough lens block is to be. Then it is set aside in a furnace, where for a month or six weeks it is slowly heated until it softens down and fills the mold; then it is as slowly cooled. It comes out looking like a rough block of sanded glass. The polishers now rub down two of the sides, until they are perfectly clear and bright, so that one may look straight through the block and make the closest examination for flaws. The best of this glass is as beautifully clear as a jewel. There are a great variety of shades, from purest white to the deep yellow of the heavy lead glasses, the prices of some of the glass reaching as much as $20 a pound. At the lens manufactory this glass is ground into lenses and prisms of every conceivable size and form, some lenses being not larger than a pin-head and as costly almost as a diamond of the same weight. Great skill is required in this work, because an error of more than one ten-thousandth of a millimeter in the curve of a lens makes it unsuitable for use in the highest grade of instruments.

Another picturesque feature of the glass works is the great corridor where the thermometer tubes are blown and drawn. In the early days of its work the Eeichsanstalt (with the governmental normal-measure commission) joined with Professor Abbe and Dr. Schott in trying to produce more perfect glass for use in making thermometers, the glass formerly used being subject to the influence of heat and cold. The result has brought all the world to Germany for high-grade scientific thermometers.

We saw this glass in process of manufacture. A boy workman caught a bit of molten glass from the furnace on the end of a blowpipe. It was hardly larger than a walnut, but by twirling and blowing and molding, it grew to the size of an orange, with the shape of an acorn. More glass was then added, and there was more rolling and blowing, and when the proper stage was reached the blowpipe was passed quickly to the brawny master workman. He in his turn added glass, blowing from time to time with cheeks outpuffed until it seemed as though they must burst, and then rolling the great ball of glass on his iron kneading board until it looked like a huge yellow gourd. Faster and faster he worked, keeping the ball always symmetrical, and yet white-hot. At length he lifted the glowing mass quickly in the air, and a second workman attached his blow-pipe to the bottom. Then the two men ran in opposite directions, twirling the pipes and blowing lustily from time to time. From a thick, portly yellow globe the glass thinned out quickly as the men ran apart, until it became a dull red tube not larger than a man’s little finger, and nearly 300 feet long. Sometime s in drawing these tubes one of the blowers would not only run the length of the corridor, but far outside on the hill. And that is the way a thermometer tube is blown and drawn. It requires only a moment in cooling, and then it is broken up into short lengths and sent to the ovens for tempering and annealing. In these rooms also are blown the finest glass for chemical apparatus, for incandescent-gaslight chimneys—30,000 of these per day—and for other purposes requiring high-grade glass.

Both of these business institutions, founded on scientific investigation, still continue their scientific work. The lens manufactory has no fewer than twenty scientists on its staff, and the glass works has five, all thoroughly schooled investigators and mostly university doctors. These men devote their entire time and attention to experimenting along chemical, optical, mathematical, and technical lines, seeking to discover new processes and establish new principles which will be of value in the business. In this way the whole institution is kept on a thoroughly scientific basis and in the foremost van of progress. This idea of a scientific staff for a business institution has its most perfect development in Germany. Indeed, science lies at the root of some of the most progressive and profitable business enterprises in the empire.

The lens manufactory, especially, has its own unique methods of doing business. A large telescope is looked upon as an artist would look upon his newest picture. It must be as perfect as it can be made, time and cost of materials notwithstanding, and when it is finished it is billed on the basis of its cost. Cheap instruments are made to provide work and training for the younger and less experienced workmen. And yet so great is the demand for the fine products of the factory that it cannot be supplied. Curiously enough, also, no patents are taken on instruments and processes, like microscopes and microscope attachments, which are used solely for the advancement of science, the men behind this unique institution having their hearts too deeply set on the advancement of human knowledge to hinder it by monopolies. The product of high-grade microscopes alone at this factory is over 1,800 a year, and each microscope comprises the work in some detail of over fifty men.

And now I come to what is, perhaps, the most interesting feature of all in these astonishing business enterprises, the feature which makes the lens manufactory in particular really more of a public institution than an enterprise for private gain.

Professor Abbe lives just across the street from the huge buildings of the lens manufactory. His home is a little one-and-a-half-story building, old-fashioned and Germanlike. It is thickly surrounded with trees and shrubs, and laid out with flower beds. At the time I saw it the lilacs were in full bloom, and the fragrance, drifting across the street, filled the rooms where the glass polishers bent low to their work. Here Professor Abbe has worked year by year, in his favorite fields of optics, mathematics, social economy, invention; and although now well along in years, he is not lacking in his zest for new and more difficult problems. Every summer he takes a short vacation in Switzerland, where the people of the village at which he stays know him merely as “the German professor.” Thus quietly he has lived, watching the factories rise around him and win him a fortune. From the first he was deeply interested in the welfare of the workingman—an interest hardly second to his love for science—and out of this interest grew the Carl Zeiss Stiftung (Institution), named from his friend, Carl Zeiss, which now controls the entire lens manufactory with its 1,200 or more workmen and owns a half interest in the glass works with its 400 workmen.

The Stiftung is unique among institutions It is the creation of a law of which Professor Abbe was the author, and it is in the nature of a corporation under state control. To this Stiftung Professor Abbe turned over all his interest in both of the great plants at Jena, retaining only a directorship. A commissioner of the grand duchy visits the works every week and assists the local directors in carrying out the tenets of the law. The purpose of the Stiftung is two-fold. First, it provides for the comfort of the personnel of the works from the directors to the lowest apprentice boy, by means of a unique system of pensions, sick benefits, profit sharing, and educational advantages. Secondly, it provides for large contributions toward the advancement of science. No one connected with the institution receives any of the private profits of ownership. Professor Abbe himself receives merely the salary of a director, which, according to the law controlling the Stiftung, can never be more than ten times the average salary of the “standard” workman of the shop—the workman who is more than twenty-four years of age and more than four years in the service of the firm. This standard workman now receives less than $500 a year. But Professor Abbe is entitled to a pension when he shall cease his active connection with the business, the same as every other employee. If it should be absolutely necessary to discharge a workman, he must not only be given due notice, but the Stiftung must pay him, if he has been employed for more than three years, a sum equal to his total wages for from six months to two years, according to the length of time he has been in the Works. And after five years’ service every workman who retires for age or invalidity receives a pension, or should he die, his family is pensioned. In this way he is absolutely secure in his work. The Stiftung sets aside a certain definite sum from its earnings every year, and this is so invested outside of the business that it will pay all pensions and discharge advances, thus making the pension system independent of the vicissitudes of the business, for even though the business failed, the money would be on hand to pay the regular pensions of old and faithful servants. Every workman is given a two weeks’ vacation every year with pay for half of it, and he is also paid in full for all holidays except Sundays. Moreover, the whole lens manufactory, with Professor Abbe at its head, is like a great family. Every month a delegate from each of the departments, thirty in all, meets with the directors and discusses the conduct of the work. These delegates are never foremen, but represent the men themselves, and the suggestions they make are from their own point of view, not from that of the foreman. Last spring the subject of shorter hours of labor came up, a subject of which Professor Abbe and the other directors had already been thinking. The workmen delegates to the conference suggested eight and one-half hours a day: the directors promptly responded, “Why not try eight hours?” Every workman was questioned, and six-sevenths of them asserted that they could do as much work in eight hours, working faster, than they could in the longer day. Lens grinding is very confining work, especially fatiguing to the eyes, and even more so to the nerves. So on April 1,1900, the experiment of an eight-hour day—a very great innovation in Germany—was begun. If at the end of one year it is successful, the plan will be continued indefinitely. The hours of work are now from 7 to 11.30 A.M. and from 1.30 to 5 P.M., the long nooning giving the men ample time to go home to dinner and to rest thoroughly for the afternoon’s work. Director Fischer informed me that the plan so far as it had been tried was a great success, fully as much work being accomplished in the short day as had hitherto been accomplished in the long day, and he thought that the work was of better quality, although the experiment had not then been in progress long enough to permit of positive assertions.

In addition to these advantages to the personnel within the works themselves, the Stiftung has spent large sums of money in other directions. I visited an extensive and highly popular free reading-room, said to be the largest institution of its kind in Germany, the Germans having always depended on the cafes for their periodical literature. A fine library building to contain a good collection of books as well as this reading-room is soon to be constructed. The Stiftung also contributes largely to the local hospitals that its workingmen may be cheaply treated; it has established special courses of instruction for its men in mathematics, physics, drawing, mechanics, and in the German, English, and French languages; it has instituted a free swimming bath in the Saale River; and it is helping to build walks and summer houses along the mountain-sides and in the forests around the town—those strolling and social spots which a German so dearly loves.

All of these advantages help to attract to the lens manufactory an unusually intelligent and productive class of workmen—and indeed for these fine operations great intelligence is required. So far as possible young men are taken and specially trained to the requirements of lens-making, and as they grow older, the cumulative advantages of the pension and profits system, as well as the short hours, tend to keep them where they are, even though tempted elsewhere by offers of higher wages.

These are by no means all the advantages which the Stiftung offers its workingmen, but they will suffice to indicate its purposes in this direction. In its other activities, science has already felt the influence of the Stiftung. It has established and equipped a fine astronomical observatory in the University of Jena, it has founded a new chair of mathematical physics, and will build a fine laboratory for experimental physics, and it is a large contributor yearly to other departments of investigation at the university. Nor are its interests confined alone to Jena, but extend to science in general, even to the considerable assistance of a recent Polar expedition. Such activities as these, and they are as much a part of the business of the Stiftung as the making of glass and lenses, seem odd enough as looked upon from the exceedingly practical point of view of ordinary business life.

The Stiftung has now been in existence nine years with great success. The profits of the business have been large, and its activities in science and in benevolence have been correspondingly large. It was the state that helped the work in the beginning by its liberal contributions of money, and enabled Professor Abbe and his associates to carry on their experiments, and now the German people, and, in fact, humanity in general, are reaping the reward. And in case the Stiftung should ever go out of business, for whatever reason, one-half of the proceeds remaining after the debts are paid will go to the city of Jena, to be used for the good of its inhabitants, and one-half to the University of Jena. Not a cent is reserved for private disposal.

Professor Abbe devotes most of his time to the working out of this great philanthropic idea. Anticipating, at the time he drew up the law governing the Stiftung, that forethought could not provide for every possible condition, he reserved to himself the right, until the year 1906, to make changes in the statute. In this way he is able to correct any errors or injustices as time and experience point them out. After 1906, however, there can be no more changes: the law will be absolute and perpetual, and as long as lenses are made at the Carl Zeiss Works, so long will its workmen enjoy advantages almost without equal anywhere in the world, and so long will science have a strong and faithful ally.


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