Popular Science Monthly/Volume 28/November 1885/Two Wonderful Instruments

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THE eye is the most wonderful organ existing in the higher forms of animal life. It is the window of the brain; through it, the creature obtains knowledge of that which lies beyond the reach of its other senses.

But there is really nothing very mysterious about the structure of the eye when considered as an optical instrument. It is simply a tiny chamber, with one little window through which light passes, making a reversed picture upon the wall beyond. The same effect may be obtained by a lens so fixed in the window of a darkened room that the only light from without must pass through it. As in the illustration we present herewith, the picture of the scene without, the peasant-girl afoot, the rustic laborer, the thatched cottage—all appear on the screen in the dark chamber, but reversed in position.

The same effect is produced by the eye. The eyeball is a little globular room. The window is so contrived that it can be made small or large, as the light is strong or feeble. From the wall in the rear upon which the picture is made, a nerve carries the impression backward

PSM V28 D060 Image seen by the brain versus the eye.jpg
Fig. 1.

to the brain, and by means of that impression we perceive. This is the mystery, how the brain gets its impression; not how the eye gets its image.

In the present article I shall not describe the structure and functions of the eye, except to show how human ingenuity has contrived an instrument almost exactly resembling it, and capable in some respects of doing far more wonderful work. Man has invented in reality an artificial eye which sees farther, with infinitely greater distinctness, and in a very much shorter space of time, nearly everything which lies before it. Almost every particular in the structure of the human eye must be imitated by this instrument. When in its most perfect condition its work is quite as wonderful as the eye of an animal.

In the first place, we must have a perfectly dark box, say about a foot high, a foot wide, and about eighteen inches long. This is the dark chamber, and corresponds to the eyeball. In one end is an opening in which is inserted a peculiar arrangement of optical glasses. These will correspond to that part of the human eye which is called the crystalline lens.

What is this? Just in front of the main body of the eyeball, behind the curtain which we see, is a transparent, circular and flattened body, thicker in the middle and thinner at its edges, the exact shape of a burning-glass. It is held in its position by a very delicate membrane which suspends it in its place in front and behind. If it were not for this crystalline lens of the eye, we should be able only to have an indistinct impression of light. This lens enables us to see the forms of things; defining them in the same manner as the lens of spectacles, or the lenses of the telescope or opera-glass. Now, in the artificial eye which we are considering, we must place, in the front part, glass lenses through which the picture or view can pass into its interior.

PSM V28 D061 Vertical section of the eye.jpg
Fig 2.—A Vertical, Section of the Eye.A, the cornea; E, the crystalline lens; I, the choroid; K, the retina; M, the optic nerve leading to the brain.

In the human eye the entire inner surface of the eyeball is covered with a brownish-black membrane called the choroid coat. Its use is to absorb light which reaches it and to prevent reflections. Now, in our artificial imitation, we must cover the entire interior of the box with black paint, so as to absorb every ray of light, except that for which we have a use.

In the back part of the human eye is the termination of the optic nerve called the retina. It is that part of the eye which is especially sensitive to light; it receives the rays entering through the front window, forms a picture of the scene, and communicates the impression through the fibers of the optic nerve to the brain behind it. How it does this we do not know. It is certain, however, that an exact picture of anything we see is created upon this membrane in the back part of the eyeball.

Doubtless the reader has already guessed the name of the artificial invention I have been describing—the photographic camera. But what shall take the place of the nerve or retina of the eye? What shall stand in place of the mysterious cells of gray matter in the brain, which receive and retain the visual impressions? After all, this is the only really wonderful part of either instrument.

In modern photography that which answers to the retina of the eye is called a "sensitive plate." It is a small plate of glass, coated with a chemical solution, so sensitive to light that it darkens the moment it is exposed to the faintest ray of sunlight. Let us take one of these plates and, with due precautions, carefully put it in the camera exactly where in the human eye the retina is situated. The camera, or dark chamber, is covered in front exactly as though the eye were closed; not a ray of light under any circumstances is yet permitted to enter it.

Now comes the mysterious part of its execution. Let us suppose that a man blindfolded, and this artificial eye, a photographic camera, are set down in the open air in the bright sunshine before the scene of some great ceremony—a procession of a thousand persons, the moving panorama of a city street, or a wide extent of landscape. Suppose that, the bandage being removed, the man were instructed instantaneously to open and shut his eyes as quickly as possible, and then to describe what he had seen in that twinkling of an eye. What would be the result?

Try the experiment yourself. Go to the window, with your eyes closed. Open and shut them just as quickly as possible, and then try to describe what you have seen in that time. It will be very little, besides that which you remember from previous familiarity with the scene. For the most part there will be nothing beyond a confused idea of light and shade. The time of this momentary vision will be too short to enable the human retina to perceive or the human brain to register any definite impression of anything.

How is it with the photographic camera and lens, our artificial eye? We will suppose that everything is in readiness, that its retina or sensitive plate is in perfect condition, and that not a ray of light has yet entered within the darkened chamber. Instead of being "the twinkling of an eye," we shall arrange so that the time elapsing between the opening and closing of the artificial eyelid shall be less than one tenth of a second, or far less than the time necessary for our eyes to open and shut. It shall be as nearly "instantaneous" as possible. Everything is ready. Click! It has opened and shut. What has it seen in that little instant of time?

If anything is in motion, it has been perceived in that fragment of a second as if motionless. Men walking along the street are pictured with uplifted feet. A trotting-horse may be caught with all of its four legs in the air, viewed just at the moment when he was clear of the ground. A man leaping with a high pole may be pictured in mid-air, precisely in the position in which he appears at the highest altitude. Motion seems rest.

But this is not the most wonderful of its powers. Far beyond the keenest of human vision is its range of sight. If the light is good, this sensitive plate of glass will have recorded and discerned a thousand uplifted faces as perfectly as the human eye perceives the features of a single countenance. Every expression of joy or sorrow, every peculiarity of dress or attitude, the leaves of a forest or the grass by the wayside, will have been seen and delineated and retained perfectly in far less than the briefest possible twinkling of a human eye.

Before me as I write is an instantaneous photograph upon glass of one of the principal boulevards of Paris, taken about noon-time. I seem to be looking down a broad avenue of lofty houses, each six stories high. I can see seven street crossings or blocks. The avenue is lined with shade-trees on either side. The street is filled with a moving panorama. So exquisitely fine are all the details that, to bring them out, I must use a small hand-microscope. Nearly fifty vehicles of every kind are in sight, all in position of arrested motion. A block distant an omnibus is approaching; the very foot-board slats upon which a passenger rests his feet I can count with my microscope. The sidewalks are crowded with every variety of Parisian costumes. Near me is a soldier touching his hat to his superior officer as he passes him, and three blocks away I can see a man sweeping the street. Schoolboys and clerks, shop-girls and mechanics, soldiers and street-sweepers, gentlemen of leisure and rambling travelers, representing every type of Parisian life, are all here. It is a picture of a Moment of Existence. Ten minutes later, and it may be not a single person here represented will be walking or riding along this street, yet the scene itself will be unchanged. The crowd continues; the atoms change.

Here is another Paris view, of a spot infinitely interesting to the historian, the Place de la Concorde. Almost in exact range we see the two fountains on either side of the Obelisk of Luxor; a quarter of a mile beyond is the Church of the Madeleine. The same ever moving crowd of human activities is here again unconsciously arrested on this plate of glass! There rises the Egyptian Obelisk, every hieroglyph as clear as when first raised in Egypt two thousand years ago. Ah! if human invention could have caused this eye to preserve for us but one glance of the awful tragedies which have been enacted on this spot! In place of those romping school-boys or laughing sightseers, once gathered on this place an eager, hungry, and bloodthirsty crowd of men and women; where that obelisk points to heaven once stood a platform, and thereon the guillotine. And one day this arresting eye might have seen Louis XVI, bending his head to the axe; and another day caught Marie Antoinette's look, as she glanced backward toward the Tuileries; or Madame Roland apostrophizing the Statue of Liberty; or Charlotte Corday murmuring, "The crime, and not the scaffold, makes the shame!" And imagine the upturned faces of that crowd!

But not only is the range of vision vastly more comprehensive by the photographic camera; it is far keener. The sensitive plate of the photographer is to-day of special use in the observatory of the astronomer. Far out in infinite space are stars which the human eye, looking through the most powerful telescope, fails to see; they are beyond its range. Yet this simple plate of glass can see them. It has a power beyond that of any human retina! Dark spaces, once considered blank, are to-day known to be full of suns, each perhaps with its retinue of planets, tilled it may be with beings like ourselves.

The future possibilities of this wonderful invention are beyond conception. It may be that for centuries hence, before war ends, and civilization triumphs in peace, the instantaneous photographic apparatus will be a part of every army equipment. There is no reason why a great battle could not be taken—aside, perhaps, from smoke-obscurity—as well as any great concourse of people. To-day the photographic artist is content to catch the movements of a race-horse or an athlete, or the panorama of a city crowd; then, perhaps, our distant posterity will be only satisfied with the instantaneous record of more important events. To-day, history is made up of confused and disputed statements; then, it may be read in the living pictures of the deeds themselves.