also, and in a recent murder trial in Berlin such a test was admitted as evidence for the prosecution. Scotland Yard and the Bank of England both have an apparatus available for making tests of this kind, and a wellknown authority has declared that for this purpose ultra-violet lamps are more serviceable than a microscope.

The health of silkworms may not be considered a very important matter, but upon it is dependent the quality and quantity of the thread produced. Ultraviolet light is now used to test whether the worms are healthy or not. The secreting organ of a healthy silkworm gives a white fluorescence, while the blood shows a yellow one. Any variation from this denotes an unhealthy insect. A possiblity of the future may be an adaptation of this method to the human body also.

Students of history have found the rays invaluable in deciphering palimpsests. In olden days a manuscript was not destroyed when time had rendered the document worthless owing to the labour and cost of manufacture. Instead, it was carefully cleaned by mechanical or chemical means and used a second and even a third time. In many cases the original script would be of far greater value to historical research than the superimposed and visible text, but hitherto this material has been unavailable. By using filtered ultra-violet rays it is possible not only to see the original writings, but also to obtain a photograph, for the tints and dyes used in the first text fluoresce differently from the later writing and also from the parchment itself. This method was perfected by Prof. G. R. Kogel of Vienna, and in a photograph which he has taken the overlying text appears as if in outline type, white lettering with a thin black edge, and underneath can be seen quite clearly the dark grey lettering of the older script. While imperfections due to the varied action of the cleaning processes must be expected, it is seldom that there are any difficulties in deciphering due to visibility.

Textiles are tested for mildew and bacterial damage, while like, but actually different, fabrics can be identified. Eggs are examined for fertility, because sterile ones fluoresce differently from fertile ones, while in dentistry the rays are used to detect decayed teeth. The ways in which fluorescence is being applied and the value of this

method to industry and technical research are incalculable, and descriptions of the many interesting uses could be continued indefinitely.

It is quite possible to take a photograph in total darkness. The camera is focussed on to the desired object and the line of the lamp beam similarly directed. Visible light from the lamp is filtered away and all other illuminations are extinguished. A simple instantaneous exposure is made with the camera, and after development the negative is fully exposed and equal to one taken by magnesium or other artificial illuminant. This is possible because the photographic plate is especially sensitive to the rays, so much so that visible light can be dispensed with altogether. An adaptation of this method is used in the making of microphotographs in metallurgy. Difficulties are experienced in focussing, which has to be done by means of a fluorescence screen and must be very exact. The advantage of the method lies in the fact that some of the constituents of steel which look very much alike when photographed by ordinary light absorb ultra-violet light selectively, and so appear sharply differentiated when a micrograph is made under this illumination.

The rapidity of many chemical reactions is greatly increased by the action of ultra-violet light, some chemical actions going on exceedingly slowly in the absence of light, but proceeding with explosive violence under ultraviolet light of short wave-length. In those industries employing chemicals largely, enormous benefit has been gained by expediting chemical processes and the sterilisation properties are also being used extensively. Recent developments in our knowledge of the action of ultraviolet light have been followed by results of great scientific and economic importance. Instead of being only a method used medicinally on the treatment of disease or even a valuable therapeutic cure, ultra-violet light has now become a most potent factor in national life, and its ramifications are continually increasing with extraordinary rapidity.

LEONARD V. DODDS.

Art. 4.-THE SUBSTANCE OF GREEK TRAGEDY.

1. Aristotle. The Poetics. Loeb Classical Series. Heinemann, 1927.

2. Tragedy. By F. L. Lucas. Hogarth Press, 1928.

FIRE and Time's 'injurious hand' have spared for our consideration a very minute part of the mass of Greek literary criticism. The great centuries of Greece were singularly free from any theorising about the principles or meaning of art and literature, for the artist was the humble and unquestioned servant of the state, active at the great public festivals or in the adornment and building of the city's temples or for occasions of social union and enjoyment. It was only when the vitality of the citystate began to fail in the fourth century B.C. and disintegrating forces made themselves painfully evident in public life, that Plato accused Art of being one of those forces and preached the necessity of putting it in leadingstrings. The fourth century was the first to hear the deceptive and distracting message of Art for Art's sake with all its isolating influence on the individual, and to witness the detachment of literature and sculpture from the service of the state, and their transformation into a grace or solace of private life. The Middle Comedy and the sculpture of Praxiteles mark the first stage in that journey by which Art passed from being the common enjoyment of the whole people in national theatre or temple into the secret delight of the solitary reader or the private collector. Art may still serve to adorn temples and amuse a public gathered in the theatre of Dionysus, but the dignity of solemn and serious feeling, which sprang from its union with the life of the state and religion, had for ever passed.

In that wonderful outpouring of a life's experience and reflexion known as the Laws, Plato is still buoyed up with the thought that the small city-state is a possibility in Greek politics. While he was writing, the power of Macedon was already established and threatening Greece in unmistakable fashion. And Aristotle, who died little more than twenty years after Plato, still clings to the outworn forms of Greek political life,

summarising the achievements of the past for the instruction of future generations. And as in the great philosophical treatises he traces the development of the Hellenic mind in ethics and politics and metaphysics so in the 'Poetics' he reflects upon the course of drama and formulates certain rules and practices which the dramatist and tragedian in particular-for we no longer have his criticism of comedy-must observe if his work is to be successful. Even if the thought came to him that Greek tragedy had attained the true fullness of growth, he gives no sign of recognising that it was already moribund, and that even in his own lifetime and for some time before, the plays publicly performed at Athens were either bloodless creatures formed of artificial rhetoric, or tragedies from the great past briefly galvanised by the art of the theatre into a second life.

Brief and fragmentary as Aristotle's book on poetry is, it is the only piece of criticism on a definite form of art, which has come down to us from antiquity, composed by one who had spoken with men who had seen and known something of the greatness of Athens in the fifth century B.C. Dionysius, Demetrius, and the author of the treatise on the Sublime are separated by centuries from the works which they discuss. Literary criticism had become a business in itself, and the feeling for the relationship of literature and life was hardly present to their minds. They concentrate too much on the verbal or formal perfection of the Greek writers, and break up that original unity of life and art which is the precious and unique quality of the creative artistic spirit in the fifth century B.C.

The preservation of Aristotle's criticism on any particular form of art is a piece of good fortune, and our sense of that good fortune is tremendously increased when the object of his criticism is Greek Tragedy. For Tragedy which has attained such an astonishing position in European literature is the peculiar creation of the Greeks. Epic and Lyric poetry are found in the writings of the East. Architecture and sculpture achieved magnificent form long before the golden age of Athens. Tragic drama seems the distinctive flower of the Greek genius into which all their other literary forms were gathered together, so that it contains the splendours of

epic narrative and the varying moods of lyric inspiration, blended into a vaster and deeper harmony than any one of those forms could achieve by themselves, the symphonic poem of life. After the repulse of Persia from Greece in 479 Tragedy becomes the supreme form of literary art in Athens. He who reads the plays of Sophocles can hardly avoid feeling how natural it is that the youthful energy and lyric flights of an earlier and youthful age should pass away into this mature form of summer beauty. Tragedy is the final experience of life as something serious. Epic and Lyric poetry may be conscious of that seriousness, but they are concerned chiefly with the slighter and more transient experiences of life, which are obscured or pass away with the years.

Tradition relates that Aristotle wrote the 'Politics' after a preliminary study of a hundred and fifty-eight constitutions. How many tragedies he had seen or read before writing the 'Poetics' it is impossible to conjecture. During his long residence in Athens he must have seen a very large number performed and have supplemented that experience by reading. We know that the three great tragedians wrote over three hundred dramas in all, and when we recall the many other writers of the fifth and fourth centuries, some of them most prolificAstydamas, for instance, is credited with two hundred and forty plays-the full roll of tragedies must have been immense, more than any critic, however voracious his appetite, could possibly digest. If his reading was extensive, Aristotle makes no parade of it in the 'Poetics.' In addition to Eschylus, Sophocles, and Euripides, he mentions by name seven or eight other dramatists and about a dozen plays by the great Three which are no longer extant. And in harmony with this simple list of references and quotations is the simplicity of dramatic principle and structure which his criticism brings to light and approves as the most successful. Indeed, so simple are his requirements for a good tragedy, that it is hard to avoid the surmise that Attic tragedy except in the hands of a very great master must have been a barren and uninteresting flat, the rehearsal with monotonous reiteration of an oppressive theme.

In reading the 'Poetics' it is well to remember that Aristotle's purpose in writing is not only to set the