exposed them for several days to sunlight, then brought them into a dark room, and found that this was indeed the case. He thought that the absorbed energy of the sunlight not only produced the fluorescence, which was a familiar phenomenon, but also these penetrating Röntgen-like rays. But one day, when for some reason the exposure to sunlight had been omitted, it was found to make no difference at all. The rays proceeding from the uranium salts were not dependent upon a previous supply of energy from the sun, nor did time bring any diminution of their power. In 1898 G. C. Schmidt was able to show that compounds of thorium send out similar rays. The minerals, which contain, among many other elements, uranium and thorium, may be called natural radio-active substances. From these natural radio-active substances far more powerful radio-active substances have been extracted by chemical means, and new elements have been discovered, the best known being radium, pure salts of which were first obtained by Professor and Madame Curie from the mineral pitchblende, a uranium ore found in Bohemia.

In the present state of our knowledge, when almost every week brings new facts to light, no generalisation on the subject of radioactivity is possible. Suffice it here to quote the words of the Times of the 26th of June of last year: 'Matter in quantities invisible under the microscope, unweighable on the finest balance, and beyond the range of detection even of the spectroscope, can be accurately studied and quantitatively investigated, if it possesses the property of radio-activity.'

Scientists are not agreed as to the source of energy of the Becquerel rays, rays capable of doing 'work' in the scientific sense of that term, without any energy being supplied from without, to our knowledge. Lodge, Crookes, Rutherford, and many others are advocates of the disintegration theory, namely, that the elements in question are disintegrating at an extremely slow rate into other elements, so that the source of energy is the internal energy of the chemical atom. Madame Curie and others think that the energy of the radio-active substances does come to them from without, that they are able to absorb the energy of rays of some sort which pass through other substances unperceived. But on this point all are at one: that the discovery of the radio-active elements is revealing facts hitherto absolutely undreamt of; that, as Professor Grätz says, there apparently is, behind the world of phenomena as we know it, an entirely unknown region the very first coast-lines of which we are only just beginning to perceive.

Such an extension of our knowledge naturally brings with it a shaking of the foundations, and at least one eminent chemist has called attention to the fact that, after all, our chemistry is only the chemistry of the means at our disposal; that our very greatest heat,

the heat of an electric arc, which breaks up all molecules into atoms, is insignificant compared with cosmical heat, and that we have no idea what the effect of other conditions might be.

It has been thought for some time that chemical affinity is really electric in essence, but it has not yet been possible to work out any satisfactory theory. On the electric theory of matter, namely, that atoms are complex-'an aggregate of smaller bodies restrained and coerced into orbits by electrical forces'-chemical affinity should admit of an electric explanation. Experiments with radio-active substances seem about to confirm the electric theory of matter in an astounding way. Of the three principal kinds of rays given off by a radium salt-distinguished by some scientists as a, B, and y-the a rays are the most easily absorbed. A metal plate will shut them off, and enable the more penetrating rays to be studied alone. These rays will produce a dot of light on a phosphorescent screen. If now electrical and magnetic forces act on the rays, then there appear on the screen a fainter, undeflected dot and a band of light; the band and dot being separated by a space. The fainter dot is caused by the undeflected y rays and the band of light by 3 rays of varying velocity. These rays are found to be streams of electrons, like the cathode rays, but with a velocity approaching one-third that of light. And the result of mathematical calculations based on the experiments was, that at velocities so high as this, the mass of the electron was no longer a constant. Now mass, if it really is mass, cannot become a function of the velocity, so it was evident that part at least of the mass was apparent and due to the inertia of electricity known under the name of self-induction. Indeed many physicists consider it proved that not only a part, but the whole, of the mass of the electron is apparent, from which it follows that cathode rays,' whencesoever obtained, consist of pure negative electricity.

And there are men who are now going a step further still. They say: If forces that are purely electro-magnetic produce exactly the same effects as would be produced by the inertia of matter, perhaps all matter is in the same sense only apparent.' At present the phenomena of physics are, as it were, divided into two camps: acoustics and heat, which are explained from the laws of mechanics; and electricity, with its subdivision light, which has not been satisfactorily thus explained. For half a century we have tried to explain electricity mechanically, and may be said to have failed; let us now try to explain mechanics electrically, and see where that will lead us.

Perhaps it is a mere matter of words whether we say that all matter is electrically charged or that all matter is modified electricity. But it may lead to the most far-reaching conclusions if, in explaining phenomena, the laws of electricity should be taken as the premiss from which we start, instead of, as hitherto, the inertia of matter. And, inasmuch as the more nearly any explanation

approaches the truth, the better does it point the way to fresh knowledge, the fact that so radical a change may be about to take place is one of the reasons why there is a feeling of expectancy in the air. It is hoped that light may be thrown upon universal gravitation and other obscure problems, and it is suspected that science is trembling on the verge of something great.

Berlin

ANTONIA ZIMMERN.

A KNIGHT OF THE SANGREAL

'SAMSON placed this cross for his soul,' runs the legend on one of the old carved stones at Llantwit Major which have the virtue, like the stone the damsel gave Peredur, of making the invisible visible. Their power comes of the names they bear, and of one in particular, more wonder-working still than that of St. Samson of Dôl, the name of a knight, 'Iltuti,' carved above a panel of interminably woven Celtic ornament. Iltutus or Illtyd is the patron saint of the church; but he is much more than that, for I believe we have in him the type and prime of those shining men that grew in medieval fantasy into the questing knights of the Holy Grail.

As one deciphers the letters on the stone shaft, and turns to look round the empty church with its air of some medieval sculptor's workshop long dismantled, and recalls his story, Illtyd seems to rise from the oppressive multitude of the Welsh saints and show himself in his natural colours. He starts to life, a Breton knight, young, ardent, hot from the chase, and dressed in a semi-barbaric dress, part Roman, part British: just as he was on the day when he gave up his hunter's quarry to follow a great mystery. That was at Llancarvan, and to understand this primitive Knight's Tale you must range further than Llantwit, and explore some of those miniature valleys, or shallow cwms, which are so like the hermit's retreats-the hollow with the cell or 'cuddigl meudwy' of the Welsh Arthurian tales; and you must certainly visit that of the Carvan where the princely hermit, Cadoc the Wise, met his young kinsman at an ominous hour. The cwm at Llantwit itself, where the churches stand by the brook Hodnant, is one of the same kind; but to-day it reminds one too strongly of the medieval people who used Illtyd's cross as a centre round which to build to let one easily translate the scene back again to its wildness. Five or six years ago, Illtyd's stone stood out in the churchyard, and then its power over the past was more certain. You could stand before it then, just as its sculptor Samuel did, when he saw it set up, and found it, I dare say, very good to look on, with its wheel-top-now unluckily lostsuperbly crowning it. You could look away from it into the trees, the actual descendants of those he and Illtyd knew, or hear the

brook babbling precisely the same busy mysterious babble to the sea below Colhugh. Or, turning away from it some autumn evening, you could hear a hoof strike on the St. Donat's road, and believe it indeed a knight that came riding down the bank: a wilder knight than that told of in the French romances, with skins of animals and feathers of birds wrought into his dress below his Roman breastplate and his torque; with a deer-skin belt, the reddish hair still on it, to carry his knife; and a great hurling spear to eke out his sword and the ringed and bossy targe at his saddle.

Arriving in Llantwit to-day, you get there by the newest of railway lines; but once arrived you pass, descending gradually, through a village that used to be a Tudor town; and street by street you knit up antiquity as you go, till you reach the churchcwm where hide-oldest things of all-the crosses of Illtyd and Howel. On the way you pass small buildings of almost every age; old thatched cottages of the true Glamorgan style, with yellowwashed walls, old inns like the Swan,' or a diminutive Tudor townhall, with an outer stair under the pent-roof and belfry where hangs Illtyd's bell. Then comes the market-square, really a squandered triangle, and more inns and more cottages, white and yellow, and a long-deserted one-story building, with a sad little Henry the Eighth window, boarded up and mysterious, out of which the last monk might have hurriedly looked on the eve of the great disruption. This points the way to the dip in the road and the deeper hollow under it, populous with graves and brown stone and broken walls. There what might be three churches set end to end stand stretched in a diminishing line, with a good Norman tower keeping guard.

Now the relation in time of these medieval remains to the old stone shaft of Illtyd, which stands in the middle church, is very much the relation which the mediæval stories, written by men of the same temper with the builders, bear to Illtyd's real story. Stripped of its pious adornments in the Vita Sancti Iltuti, it becomes one of the most moving of what may be called the renunciation episodes' to be found in all the Arthurian cycle, early or late.

Illtyd Farchog, Illtyd the Knight, came of noble Breton stock. His father, says the monkish chronicler, was a soldier most famous, and found his way presently across from Brittany to Arthur's court. In that day the people of Siluria and Armorica were drawn closer together than they are now. Fostering winds and favouring seacurrents apparently made their intercourse habitual. When wars gave out, or tribal feuds grew too deadly, or the wolf-hunting was over in the deep forest beyond Carhaix, the Breton chief thought nothing of crossing to some ancient port like Porthkerry, on the wild Glamorgan coast, having some claim or tie of kindred to help him to his welcome in the Welsh regions of a hospitable King Arthur or King Saul. In that way Illtyd came, and we can gather