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this work were not many in number, but the chief centre of investigation was one known for its microscopes from Tokio to St. Petersburg, and from Buenos Ayres to San Francisco, — the house of Carl Zeiss of Jena. Dr. A. Köhler of their scientific staff designed the apparatus. Dr. M. von Rohr, another member of their staff, worked out the difficult computation of the objectives. At first the work progressed along the lines of violet light, which contains the shortest visible waves of the spectrum. As the research went on, however, it turned gradually but certainly towards the use of the ultraviolet. No simple problem lay before the workers. Microscopes had always depended upon the sun for light, and the use of a new illuminant meant an overturn of the work of many years. To obtain a microscope which should successfully substitute ultra-violet for white light, required a whole series of changes and developed new requirements which appeared in succession.

It was of the first importance to secure a source of energy which would give a constant unvarying supply of ultraviolet waves. Fortunately there was such a source at hand. If we pass an electric current between two poles made up of either metallic cadmium or magnesium, that is to say, if we form either a cadmium or a magnesium arc lamp, there will be given off a number of light waves, visible and invisible. Among these latter waves are some of the shortest and swiftest, and, as a result, some of the most useful of the ultra-violet. One serious difficulty with white light has always been what is known as chromatic aberration, its constant tendency to break down into its component colored parts. Look at an ordinary pin through a common lens, and see the red, yellow, or blue of the spectrum appear around it. The lens, unable to transmit the white light from the pin as a whole, has broken it down into its component parts as it passed through. For that reason, the matter of chromatic aberration has been a fruitful and con

tinual source of trouble in glass lenses. It seemed especially advisable to do away with mixtures of colors in this new microscopic work, and to get rid of illumination made up of waves of different rapidity. That could not be done with white light or composition light, but it could be accomplished by taking a wave of a single length out of the ultra-violet. If that could be achieved, a light of a single tone would be obtained which could not break down when passed through lens or prism, because there was nothing for it to break into.

To separate out such a monochromatic ultra-violet light, to get it where it would illuminate the object below the microscope, and to pass it through the microscope itself, some substance other than glass had to be used. Glass, permeable as it is to white light, is opaque to ultra-violet waves. Place a bit of glass across the path of such rays and you raise as complete a barrier as if you raised a wall of iron. The search for some substance which would transmit these waves was long and arduous. It was ultimately found. Fused quartz would let the waves pass through. With that discovery, the two major difficulties were practically settled. The ultra-violet source of illumination was certain to give a far greater resolving power than white light had ever given. It would pass through quartz as white light does through glass. By quartz prisms the experimenter separated out a single-toned wave of ultra-violet light, passed it up to a quartz reflector, sent it from there through a slide, and finally through quartz lenses. At the slide where the object to be examined rests, be that object what you will, a colony of typhoid germs, or a group of blood corpuscles, opens a whole new set of difficulties. As ultra-violet waves are invisible to the human eye the appearance of an object illuminated by that light makes the word "illuminated seem a misnomer. We see nothing but blackness. That lack of visual power might years ago have been a barrier, but now photo-micrography,

the art of photographing with a microscope, is so advanced that it offers an easy solution of that question. Photography can be accomplished without white light. Not only can it be accomplished, but it is far easier when done with ultra-violet waves, since the essential rays of white light which break down the chemical salts, and impress the image on a photographic plate, are the so-called actinic rays. These are found in greater quantity in the waves above the violet than in those below it. Photo-micrography, which uses the ultra-violet, gives beautifully sharp, clearly-defined images.

There is, however, another lion in the way before this process can be used. A camera or a microscope must be focused, the lenses must be so placed as to give a clear sharp image on the plate. When the eye can bring a sharp image from a blurred outline, focusing is a simple matter; but here, when the eye is of but little avail, it becomes a tedious and difficult process. An approximate focus can be obtained from that property of the ultra-violet waves by which they impart a glow, fluorescence, to uranium glass. In focusing by this process, a piece of uranium glass is placed on the slide on which the object is to rest, the light is turned on, and the microscope adjusted as the glow sharpens or grows dull. This is, however, more or less of an expedient. For more careful work, a series of films are exposed in succession. The focus is changed and noted for each exposure, and the one giving the sharpest image is chosen.

More than one microscopic tool which has proved a useful servant in the past becomes with ultra-violet light a serious hindrance. The ordinary microscopic slide on which the specimen rests is of glass, sealed with Canada balsam, a substance through which light passes exactly as it does through glass. Such a slide. placed beneath an ultra-violet microscope instantly cuts off all illumination. None of the waves will pass through. Therefore the slides, like everything else

through which the ultra-violet waves pass, were necessarily made of quartz. The old liquids which held the specimens were likewise impassable to the rays. To obviate this, a mounting fluid, a substance which would afford a food and home for germ growths, was prepared by using a solution of salt with agar (a nutrient), in distilled water. This mounting fluid gave nutrition, non-distortion, and, most of all, transparency to the rays.

When all these changes had been completed, a microscope was obtained of practically the shape and construction of a compound microscope, having eyepiece and objective of fused quartz instead of glass, having quartz prisms for transmission instead of glass mirrors, and slides of quartz instead of glass. The source of illumination had become short, swift, single-toned waves of ultra-violet, instead of long complex waves of white light. What will this instrument do? It will do just double what the old can accomplish. It will show an image of objects just half the size of the smallest the most powerful visual microscope in the world can show. Reduce it to that essential necessity already stated, the ability of the microscope to separate two points near together, and the figures show the tremendous advance. With glass lenses and visible light, the ultimate boundary for separating two such points is one twenty-thousandth of a centimeter. With quartz lenses and ultra-violet waves it is half that, one forty-thousandth of a centimeter. At one bound the new microscope has added one hundred per cent to the power of the old.

If the new microscope did nothing more than that it would be one of the great advances of the century, but there inheres in it another power which promises great future use to medical and biological science, — its action on organic tissue and micro-organic life. The science of microscopy, much as it has given to the world of knowledge which has to do with body-building, with disease, and with the infinitesimal inhabitants of our

world, has been at best a science of dead things. As the astronomer gazes at a dead world on the moon, so the microscopist has gazed through his lenses at a bacterial world made up of dead microorganisms, and of organic tissue hardened and distorted from its natural form. With the visual microscope such conditions were inevitable. The light of day would not show tissue properly until it had been so hardened and fixed by the fluids used in preparation that its normal appearance was gravely altered. It would not show cavity or bacterial form until some colored liquid which mapped out the specimen was injected into it. Such liquid perforce killed the specimen, yet it was essential to proper examination. To recognize the necessity for this, suppose for a moment that we desire to study the structure of a jelly fish. As we hold the semi-transparent mass up to the light, the cavities within by no means show their whole structure or extent. If, however, we could inject into them some brilliant crimson fluid which would fill every channel, we can readily imagine that every tube and hollow would stand out, mapped in red upon the yielding surface. So staining, for microscopic use, mapped out the specimen in the slide and gave clear definition, but as it gave that definition it killed or changed the substance.

As the experimenters carried on the new work and at last forced the light of the ultra-violet through every part, they first tried specimens prepared as for the visual microscope, but, to their surprise, they found that every kind of treatment, such as hardening, mounting, staining, made the specimen absolutely opaque to the rays. No result could be obtained. They went from prepared specimens back to fresh and live specimens. Right there developed one of the most interesting features of the whole matter, the fact that ultra-violet light is selectively absorbing. Just what does that mean? Simply this, that this light is so extremely sensitive to minute

changes in the thickness of any substance through which it passes, that the slightest difference in density makes a marked difference on a photographic plate exposed to that light. Every hollow, every cavity of tissue must have a boundary wall to separate it from the flesh or tissue about it, and those walls must be thicker than the surrounding mass. With rays far more potent than those of white light the ultra-violet maps out the whole interior of a specimen, and shows the boundaries of every part. In like fashion a red staining fluid might map our jellyfish example, or would map a microscopic specimen. That opens instantly, not only the world of organic tissue, unhardened, unmounted, and unstained, but it also opens a wide untrodden field, the study of the living bacteria. Sunlight would not reveal the history of the living germ.

The ultra-violet can trace that history from its beginning to its end.

With the new microscope we can imbed a typhoid bacillus in a solution where it can live its allotted time of existence under constant observation. We are able to study germ processes of growth, methods of reproduction, the spread of disease, and the effects of inoculation. The winding way of the blood corpuscles, of those myriad travelers which carry with them disease and cure, can be traced as never before. The struggle between the toxins and the anti-toxins opens to our view. Once more, the ultra-violet microscope has not opened up a single road. It has opened up a new world.

No advance in science moves with ordered ease. Each new achievement comes from constant struggle, from a persistent overcoming of obstacles. The new microscope has been no exception to this rule. The effect of ultra-violet light upon living matter seemed at first a barrier which might check the onward movement. It was claimed that these rays, having serious physiological effects, would kill protoplasm and render it opaque to the short waves of light. This theory has now been proved incorrect. In recent experi

ments typhoid bacilli were exposed to ultra-violet rays without harm for some forty minutes, an exposure distributed through a period of three hours. The focusing still remains a serious obstacle. Whether it be done by fluorescence, or by the taking of a series of photographs, the two methods already described, the process is long and vexing. The preparation of specimens has been difficult in the extreme, and the evolution of satisfactory mounting media, a matter of recent development, is still under discussion.

Until we have one vital piece of evidence, complete proof of what this microscope can do will be impossible. For that we should possess a complete series of comparison pictures, showing numerous instances of the same subject taken by ultra-violet and by white light under precisely similar conditions. An apparatus which will give us such an ocular demonstration is now under process of construction, and we shall in time have plates which show the exact relative values of old and new. Then pictures will tell the tale. Until that time we

shall have to do our best with words.

So ends the beginning of the story. Only the beginning, for years of patient labor, tens and hundreds of researches, will not complete the tale. Yet a great thing has been done. The black spots on the earth-maps that stand for unexplored countries are growing smaller and smaller. The light is vastly greater than the shrinking dark. Few strange lands are left for the geographer to chart or for the explorer to search out. But in another world, the world of science, all about the light of the explored hang heavy clouds of the unexplored. Not a science but is inclosed by a blackness of unknown extent, which hides many of the basic truths of each individual branch of the study of nature and her laws. What is electricity? What is the ultimate composition of matter? What is life? How that list could be extended! Every now and then by patient search a key is found that unlocks a door in the black wall, and a great new country is opened to the explorer. Such a key has been found in the ultra-violet microscope.

UPON READING AN APPRECIATION OF ALDRICH

BY HARRISON S. MORRIS

FROM the hard clamor of the brazen throat,
Man's moving legions in the metal street,-
How shall we find the tranquil old retreat
With thatchen quiet and the robin's note?
How shall we fly from millionaires that bloat
The yellow acres into pits of wheat,
Distilling commerce from the crocus sweet,
Straining a profit from the Shepherd's oat?

Ah, into thy cool close of verdurous verse,
Aldrich, I turn and find a green recess
Where the pure simples of Parnassus nurse
Mine ear offended, and 'my heart's distress
Where rumble of the inevitable hearse
Stirs not a leaf of life's seclusiveness.

--

THE REVIVAL OF THE POETIC DRAMA

BY BRANDER MATTHEWS

THE divorce between poetry and the drama is acknowledged to be most unfortunate for both parties to the matrimonial contract; and those of us who have a warm regard for either of them cannot help hoping that they may be persuaded soon to make up their quarrel and get married again. The theatre is flourishing more abundantly than ever before; and the prose-drama of modern life, dealing soberly and sincerely with the present problems of existence, has at last got its roots into the soil, and is certain soon to yield a richer fruitage. Perhaps it is even not too much to foresee the possibility of a speedy outflowering of the drama in the next half-century, in the English language as well as in the other tongues. In all the earlier epochs of dramatic expansion, in Athens, in London, and in Madrid, in France under Louis XIV and again under Louis Philippe, the masterpieces of the art have been truly poetic, in theme and in treatment. Have we any reason to suppose that our coming drama will also be poetic, both in essentials and in externals?

If the law of supply and demand were as potent in the arts as it is in commerce we should be justified in expecting that return of the poetic drama which is eagerly awaited by all who cherish the muses. But when we station Sister Anne on the watchtower and when we keep on asking if she sees any one coming, we ought to have in our own minds a clear vision of the rescuer we are looking for. When we cry aloud for the poetic drama, what is it that we stand ready to welcome? Of course, we do not mean that bastard hybrid, the so-called closet-drama, the play that is not intended to be played. A mere poem in dialogue, not destined for performance by actors, in a theatre, and be

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fore an audience, may have interest of its own to the chosen few who can persuade themselves that they like that sort of thing; but it is not what the rest of us The poetic drama, in its most splendid periods, has always been adjusted to the playhouse of its own time. It has always been dramatic, first of all, and its poetry has been ancillary to its action. In the theatre, and not only in the library, do we desire now to greet the noble muse of tragedy with her singing

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The closet-drama is like poverty in that it is always with us; and it is far removed from the poetic drama which we hoped to see revived in our language. But what is the exact nature of this poetic drama that we long for? It is not or at least it ought not to be a sort of dramatized historical novel, full of high deeds and pretty words, a costume-play in blank verse, as empty of true poetic inspiration as the Virginius of Sheridan Knowles or the Richelieu of Bulwer-Lytton. In the illuminating address on "Literature and the Modern Drama " which Mr. Henry Arthur Jones delivered at Yale in the fall of 1906, he asserted that playgoers on both sides of the Atlantic have a notion that a costume-play, with its scenes laid anywhere except in the last half-century and its personages talking "a patchwork diction, compounded of every literary style from Chaucer to a Whitechapel costermonger," has a literary distinction and a profound significance "which rank it immeasurably above the mere prose play of modern everyday life," and which give to the ravished spectator an elevation of mind and "a vague but gratifying sense of superiority."

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Probably this notion is to be found in the heads of not a few playgoers, pleased

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