is taken from it every few weeks. It may be likened also to Draupnir, the ring of Odin, which, after being placed by him upon the pile of his son Baldur, acquired the power of dropping every ninth night eight rings of equal weight with itself. Whatever may be the atomic changes by which the energy manifested by radioactive substances can be explained, we have the fact that radium salts continually produce sufficient light to be observed readily in semidarkness, heat enough to be appreciably warmer than other objects near them, rays which have an energetic action upon photographic plates and by which radiographs can be taken, and emissions which blister the skin and produce other remarkable physiological effects. It is, perhaps, fortunate that the new element is probably the rarest in the universe. Pitchblende, from which radium is obtained, is comparatively rare, and only about one and a half grains of a radium salt can be extracted from a ton of pitchblende ore. Röntgen rays, radium and radium emanation are all now largely used by physicians, not merely as means of diagnosis, but for curative purposes. Early experimenters with Röntgen rays did not realise the extraordinary powers of the rays to produce virulent effects upon the skin long exposed to them. The X-ray burns thus caused are most intractable, and usually the hand or arm badly affected by them has to be removed to prevent further extension or death. Odin bought for himself wisdom at the price of his right eye, but it was Tyr who, among all the Aesir, was held by the Norns or Fates of northern myths to be worthy of the highest honour, for he sacrificed his strong right hand not for himself but for others. This is what was cheerfully done by several early workers with X-rays, notably Dr. Blacker, of St. Thomas's Hospital, and Mr. Harry W. Cox, who were the first martyrs of the rays, and Dr. Hall Edwards, whose left arm had to be removed. Mankind should not forget the names of these and other experimenters by whose sufferings increased knowledge has been attained. Operators with X-rays now protect themselves from injury by using screens which shield them, but in the early days the necessity for such precautions was not understood. The rays are now kept under control, and their power of affecting animal tissue is used to cure instead of being harmful. In certain diseased conditions, local application of Röntgen rays has been used with marked success, and the field of their utility will certainly extend as improvements are effected in their technique. Radium has proved to be a valuable agent for the removal of certain ulcers and small cancerous growths, but neither it nor X-rays can at present be looked upon as a cure for cancerous growths of large size. In many cases, radium emanation is more convenient to use than its parent; for it can be inhaled, and when dissolved can be injected into the body tissues, or swallowed. We are only just beginning to learn something of the biological significance of the new rays; and no one can yet predict with confidence the beneficial action which the next generation will discover in them. CHAPTER XII TOWARDS INFINITY Go, speed the stars of thought On to their shining goals. Emerson. God has placed no limits to the exercise of the intellect He has And still your eye is looking on the ground. Dante. A thorough advocate in a just course, a penetrating mathematician facing the starry heavens, both alike bear the semblance of divinity. Goethe. Trees in their blooming, Tides in their flowing, Stars in their circling Tremble with song. God on His throne is Eldest of poets: Unto His measures Moveth the whole. W. Watson. WHEN the stars sparkle upon the azure canopy of heaven, the human mind seeks silence and solitude to contemplate them. It is upon such an occasion that man realises he is face to face with infinity; and, as his soul is uplifted, a sense of helplessness fills him, and the spirit of David makes him ask of his Creator," What is man, that thou art mindful of him? and the son of man, that thou visitest him?" If these devout thoughts inspired the Psalmist when he considered the heavens, what words are now adequate to express the feelings to which increased knowledge of the universe should give rise? Less than three thousand stars can be seen when a watcher, unaided by optical power, looks upward on the finest night; but even a small telescope or field-glass will show many times this number. With the great lenses which are directed heavenward in these days, it is possible to see one hundred million stars in the whole celestial sphere, instead of the few thousand visible to the naked eye. Carry your mind back to pre-telescopic times, and consider what was then conceived to be the content and extent of the universe visible to man. Nothing could be known of the stars and other celestial objects beyond the range of unaided vision, and not the boldest of the speculative philosophers imagined that there were millions of celestial bodies in addition to those which were within their bounds of knowledge. What they saw seemed to be the beginning and end of things celestial, and there was no thought of anything beyond it. Astronomy, more perhaps than any other science, teaches the imperfection of human understanding, and hesitates to set limits to the planes which may be attained in the future. Celestial things are rarely what they seem. A brilliant sky at night gives the impression of infinite calm and peace, and we speak of the "fixed" stars, whereas not a single one is at rest, and many are moving through space with velocities greatly in excess of any express train on the Earth. It is difficult also for anyone unacquainted with astronomy to believe that the Earth, and other members of the Solar system, in addition to their movement of revolution around the Sun, are being carried by the Sun into unknown regions of space at the rate of nearly a million miles a day, yet that is certainly the case. Through every year, every hour, every minute of human history from the first appearance of man on the earth, from the era of the builders of the Pyramids, through the times of Caesar and Hannibal, through the period of every event that history records, not merely our earth, but the sun and the whole solar system with it, have been speeding their way towards the star Vega, on a journey of which we know neither the beginning nor the end. During every clock-beat through which humanity has existed, it has moved on this journey by an amount which we cannot specify more exactly than to say that it is probably between five and nine miles per second. We are at this moment thousands of miles nearer to Vega than we were a few minutes ago; and through every future moment, for untold thousands of years to come, the earth and all there is on it will be nearer to that star, or nearer to the place where the star now is, by hundreds of miles for every minute of time come and gone. When shall we get there? Probably in less than a million years; perhaps in half a million. We cannot tell exactly; but get there we must if the laws of Nature and the laws of motion continue as they are. To attain to the stars was the seemingly vain wish of the philosopher; but the whole human race is, in a certain sense, realising this wish as rapidly as a speed of six or eight miles a second can bring it about. Prof. Simon Newcomb. The Sun itself deceives us by its appearance; for what we see of it is relatively small in comparison with the vast sheets and rays of luminous matter that surround the brightly visible disc, and are revealed only during a total eclipse. If the Sun could be seen from a point outside the Earth's atmosphere, it would appear more blue than the yellow tint with which we are familiar. Surrounding this bluish ball would be seen a brilliant scarlet layer like a sea of flame, from five thousand to ten thousand miles deep, out of which enormous masses of incandescent gas would be tossed |