Photography - Recent Discoveries And Applications
( Originally Published 1898 )
IT would be difficult to name a branch of science—hardly a department of industry—that has not benefited from photography. During the sixty years that have elapsed since the announcement of the joint discovery of Niepce, Daguerre, and Fox-Talbot, light as chemist has not only broadened and deepened our sight, but has revealed to us wonder after wonder, secret after secret. More marvels, indeed, have been the result of the penetrating eye of photography than perhaps of all the sciences combined during the previous hundred years.
Something has already been said anent the triumphs it has achieved in registering " the belted zone of the spectrum," and supplying a perfect method of obtaining visible images of the actinic rays. It has given us pictures also of the moon, the stars, and the nebulae. Eclipses it has recorded for us, and by its aid we have obtained drawings of the transit of Venus. The sun's corona has been depicted for us by means of its magic pencil, while, in like manner, it is giving us day by day the history of the spots on the great luminary's disc which are supposed to mark the birth and development of volcanic movements in the body of the orb that are not without their physical and moral effects upon our daily lives.
One of the latest astronomical triumphs of photography is perhaps Professor J. E. Keeley's " spectroscopic proof of the meteoric constitution of Saturn's rings." All students of astronomy are acquainted with Maxwell's mathematical demonstration that the rings of Saturn consist of an immense number of separate small satellites revolving round the planet in circular orbits. These separate bodies are so small that it is hardly likely we shall ever be able to observe them as such in the telescope, and it seemed probable that we should have to be satisfied with the mathematical demonstration of their existence. It is needless in this place to go into a description of Professor Keeley's method of working. Suffice it to say that by means of photography he was able to clearly establish the meteoric constitution of Saturn's rings. More-over, in addition, his photographs give us " the data for estimating the period of rotation of the planet, the mean period of rotation of the rings, and the rate of motion of the whole system in the line of sight due to the revolution of the planet round the sun."
At all the leading observatories throughout the world the aid of photography is being used for the mapping out of the heavens ; and to its delicate retina has been revealed myriads of stars that were beyond the ken of the most powerful magnifying glasses. This may seem strange when it is considered that astro-photography can only work by means of the telescope. But it ceases to be surprising when we bear in mind that any light or other energy—albeit invisible and impalpable to the senses—capable of affecting the sensitive surface of a photographic plate exerts a cumulative action. Thus, while an astronomical watcher at the first moment of observation may see a hundred stars, as he continues to gaze his eye becomes fatigued and he beholds fewer and fewer. But the photographic plate, in place of tiring, goes on augmenting impressions, until at the end of half-an-hour it may have seen a thousand or more times as many, though it began by noting only the same number.
Analogous to these triumphs in the vastitude of space are the achievements of photography in the realm of the infinitely small. By the aid of photo-micography we have been enabled to take the portraits, so to speak, of disease-bearing germs, and for the better study of their structures to throw them, by means of the optical lantern, greatly enlarged upon screens. In the same way all the various parts and tissues of our bodies may be, and are, studied by the aid of this handmaid of the sciences. These are, for photography, long established achievements; but there is another department of anatomical science in which the triumphs of the art are so recent that the novelty and wonder of them are still fresh in the public mind.
Most persons will remember the sensation caused throughout the civilised world by the announcement that a German scientist, Professor Rontgen of Wurzburg, had succeeded in photo-graphing the bones of the hand through its covering of flesh by means of the rays proceeding from a spherical glass tube or bulb.
Some twenty or more years ago, it should be explained, Hittorf and Goldstein, two German physicists, observed that in tubes of this description the light visible to the eye, going from one electrode to the other, was due to the imperfection of the vacuum in the tubes, and that the more carefully the vacuum was made the weaker the light became, until it totally disappeared when the vacuum was rendered perfect. They noticed, further, that at this moment the glass of the tube became fluorescent, and from the circumstance they inferred that the fluorescence was caused by the oscillating discharges of invisible rays, of which the cathode was the point of origin.
Such spherical tubes—known from the circumstance that Professor Crookes .was the first in England to experiment with them as Crookes'
tubes—were the instruments by which the New Photography was first observed. In the early part of 1894 Lenard, at Bonn, showed that it was possible to secure shadows of objects through optically opaque substances, and to obtain an impression of these shadows on photographic plates which could afterwards be developed and fixed by ordinary photographic methods. So modestly was the fact announced, however, in the midst of other and more striking novelties, that even those who read Lenard s paper when published had well-nigh forgotten that such " shadow-graphs" had been obtained by him, until their attention was called afresh to the subject by the announcement of Röntgen's more sensational discovery.
It was towards the end of 1895 that, experimenting with the spherical tube, Rontgen observed that a hand held betwixt a bulb electrically charged and a sensitized plate did not completely arrest all the cathode rays. He found that the soft parts were transparent, while the bone remained opaque, and that, in a word, it was possible, by means of a Crookes' tube, to obtain an outline of the skeleton of the hand upon a sub-stance ordinarily sensitive to the light. Rontgen gave to these invisible and penetrating radiations the name of X-rays. Within a few weeks of their first announcement there was scarcely a physical laboratory in the world but was the scene of experiments that were soon extending the range of the new Photography.
In these experiments there is no question of a camera, or even of a lens, so that they are photo-graphic only in so far as a sensitive surface is changed by the action of light, and as the result an image of the object is left upon the plate, and made permanent in the usual way.
Most persons are now familiar with the photo-graphs obtained by means, of the Rontgen radiations, which, at first an object of curiosity only, were soon found to be of great use in surgery by rendering it possible to discover the exact position of a foreign body, like a bullet, a needle, or other metallic substance in the system, or to examine a fracture or malformation.
But the importance of Professor Rontgen's accidental discovery—for it appears in the first instance to have been a happy chance—does not rest with its applicability in surgery. It opens up questions of enormous magnitude. Several theories have been advanced to account for the phenomena. One is that the X-rays may be ultra-violet light with vibrations about a million times greater than ordinary light; another, and the most sensational, is the supposition that the Rontgen radiations may be the missing longitudinal waves in the ether—a theory which, if true, would open up a department of physics as large as those of light, sound, electricity, or even the theory of gravitation itself. Whatever hypothesis may prove to be the right one, there is no question that the phenomena involved in the new Photography have "brought us face to face with facts which would only a short while ago have been considered improbable, if not impossible." Thus a new realm for scientific exploration has been disclosed, and no one knows whither it may tend or what fresh surprises it may have in store for us.
Hardly less of a surprise than the X-rays to the general public was the development of photography in the form of the Kinetoscope, the Cinematograph, the Theatrograph, etc., but in general popularly referred to as animated photography." The idea was not new ; it had long been known as the wheel-of-life or the zootrope. Marey made use of it in his researches touching animal locomotion. Muybridge carried the matter a step further by means of a battery of cameras. Mean while the highly sensitized film was introduced, making it possible to secure an image of a moving object in the smallest fraction of a second.
The moment was ripe for a further advance in regard to the photographing of objects in action, and W. Friese-Greene appears to have been the first in the field with his patent for an apparatus, half camera, half optical lantern, whereby he proposed (1) to take a series of instantaneous photographs of moving scenes upon a long band, and (2) to throw them, enlarged, upon a screen, whereon, by means of a handle, the successive pictures would be moved so rapidly as to give the appearance of life.
But, although Friese-Greene's original patent was taken out in '889, he was anticipated as regards the actual production of his invention in public by Edison's Kinetoscope. This may be called the animated photograph in little. It was soon followed by the Cinematograph of M. Lumiere of Paris, whose exhibitions of this form of photographic realism in London caused no small surprise in the early part of 1896. Previously, however, Mr. Birt Acres had exhibited similar animated pictures before the Royal Photographic Society by means of a specially designed optical lantern. At first the lifelikeness and substantiality, so to speak, of these living pictures were greatly marred by vibrations and a general jerkiness of motion ; but modifications and improvements in the apparatus soon eliminated these imperfections, and the verisimilitude to the actual moving scene became almost perfect.
The development of motion pictures during the last decade has been stupendous. In 1912 there were about 16,000 "movie" theatres in the United States, with a daily attendance estimated at 7,000,000. They have become a force, not only in popular recreation, but in education as well.
Among the more notable things connected with photography of late years has been the great advance made in regard to developers. Much has been said about these in the foregoing pages; but it will be necessary to say a few further words about them. To many operators a developer is simply a chemical compound which brings out the latent image when applied to the exposed plate. But in truth the developer is more than that, and the sooner anyone who takes up the study of photography frees his mind from such an idea the better—if, that is, he would be an artist as well as a wielder of the camera.
Captain Abney has said that the development of the latent photographic image is both an art and a science in one, and anyone who has had much experience with the developing bath will readily endorse the statement. In short, development is to the photographer much what the brush is to the painter, or the chisel to the sculptor: it gives him the power of drawing out his picture from the hiding-place on the plate, and in-fusing life or lifelikeness into it.
To the eye of course the exposed plate presents nothing by which it may be distinguished from the unexposed one. The impression it has received through the chemical action of the light is said to be latent; and it is for the combined science and art of the photographer to bring this to view by reducing the silver in those parts that have been acted upon by the light to the metallic state. This he is enabled to do by means of the various developers at his disposal.
There are so many that the question as to which developer it would be best to employ in a given case is not an easy one. The true crafts-man, however, does not quarrel with the wealth of implements or material at his command, but rather sets about making himself thoroughly acquainted with them one by one, and having satisfied himself as to the best for his purpose for the time being lays the others aside.
As already shown, the developers in more general use are pyrogallic acid and ferrous oxalate, to which may be added hydroquinone. These are usually found enough for all ordinary requirements. The last few years, however, have seen a number of new developers brought to light, and all of them have their special uses, and, it may be added, their special admirers.
Of the eikonogens, amidols, metols, rodinals, etc., it is not necessary to speak in any great detail. Are not their constitution and qualifications set forth in all the photographic journals and manuals ?
Eikonogen, which was introduced in 1889 (though discovered by Professor Meldola in 1881), is accounted a good developer for quick exposures. It gives fine detail, and a soft, albeit somewhat thin, black picture, with delicate half-tones. For density (that is, opacity), the solution should be strong in eikonogen, with potash carbonate added as an accelerator; while citric acid is recommended in preference to bromide for preventing fog and correcting over-exposure. Some hold it specially useful to portrait negatives.
Amidol acts with great rapidity, especially when dissolved in a solution of sodium sulphite, which acts as an accelerator. It yields excellent detail and good density, and is a specially useful developer for " snap-shots " and lantern-slides. Mr. J. A. Wilson considers amidol superior to any other developer for bromide paper. Metol gives a fine soft negative, is rapid in action, and capable of bringing out good detail. With pot-ash carbonate as an accelerator, fair density is obtainable. Metol is peculiarly useful for plates that have received a minimum of exposure, and is, perhaps, along with amidol, better qualified for hand-camera work than for time-exposures, where-in the image is produced with so much force that development is not so easily kept in hand as with a more deliberate agent like pyrogallic acid.
Hydroquinone is intimately allied with pyrogallic acid—or, briefly, in photographic parlance, "pyro "—in chemical composition. It was suggested by Captain Abney, the doyen of photo-graphic experts, in 188o, in place of pyrogallic acid ; and gradually, year by year, it has gone on superseding that developer, especially for films —experience showing that the negatives developed by it not only show more detail, but a crisper and cleaner image. It is somewhat slower, however, than pyro, while it gives greater density than either amidol or metol. Indeed, some object to it because of what they consider its tendency to yield harsh negatives. This is a fault which is easily overcome by careful management, using a dilute solution and proceeding with de-liberation. It shows less tendency to fog than most developers, and is, without doubt, capable of producing excellent results.
Glycin, another of the newer developing agents, acts more like pyro than like either amidol or metol. It is very slow in action, and, like hydroquinone, has a tendency to hardness if not kept well under control. Bringing out the image very gradually, and gathering opacity with the appearance of the details, glycin is specially well adapted for copying maps and drawings, and for photo-mechanical work generally. It has also been recommended for very brief exposures, as, for in-stance, those varying from a hundredth to a thousandth of a second. The colour of the negative is a clear greyish black, and there is great freedom from veiling. With glycin, bromide of potassium acts as a restrainer.
Rodinal is a very concentrated form of paraamidophenol, with which is combined sodium sulphite and caustic alkali. It is a good all-round developer, very well adapted for hand-camera work, and, generally, for getting as much as possible out of a plate. Seeing that it does not act as an agent to fog the picture, development may be considerably protracted, not only without detriment, but greatly to the advantage of the negative as regards softness and harmony of detail. The colour of the deposit given by rodinal is of a bluish-black.
All the above-named developers are used in solution, in conjunction with either an alkali or an alkaline carbonate, apart from which they can hardly be said to have any developing power at all. They all require the presence of sodium sulphite or of potassium metabisulphite to obviate staining of the film; and, if allowed to act upon the plate for a sufficient length of time, they would reduce some of the silver salt which had escaped the action of light. In the case of ferrous-oxalate, however, we have an agent of a totally different type.
This compound was first suggested as a developer for dry-plates by Carey Lea, of Philadelphia, twenty years ago. It was slow, however, to gain popular favour in England—partly, as would appear from the difficulty of preparing it ; and it is still very much in the background in comparison with the position it holds on the Continent and in America, although in both places it is giving way before late corners of the metol order. In England, however, it has been found extremely useful for bromide paper—" a purpose," says the Year Book of Photography, " for which it is still extensively employed, and for transparencies, and in scientific work where a clear black image is required, and where its inertness as regards an unexposed plate may be taken advantage of." Amongst its other good qualities may be named the extreme simplicity of its use, its cleanliness, and the ease with which it is worked. The energy of ferrous-oxalate as a developer is enormously augmented by the addition of a few drops of sodium hyposulphite. The negative is thereby greatly increased in strength, while the high lights of the picture appear almost at once.
Notwithstanding all these powerful rivals, it is due to pyrogallic acid—the first and, for a time, the only developer—to say that it still holds a fair position in the race, and proves itself very hard to beat. Many, indeed, prefer it to all other developers—partly, of course, because they are so used to it, but in no small degree because it possesses a very wide range of usefulness.
It need hardly, perhaps, be added that to use these and the many other substances useful for development—and every powerful absorber of oxygen, soluble in water, is such to a greater or less extent—to the best advantage, a sufficient knowledge of chemistry is essential; and anyone taking up photography as a serious study cannot be too strongly urged to prepare himself by a thorough grounding in that useful science.