not come off. However, they got their bags of sugar plums all the same. The inevitable address was got through in dumb show, and we were followed not only to the water's edge but into the water itself by the affectionate farewells of all the poor people. It was so touching, the way they brought gifts. Modeste was there with oranges and eggs in each hand. Indeed, I may mention here that eggs, however fresh, are very embarrassing tokens of affection when given in dozens. I presented all mine to the fo'castle, as well as sundry sacks of oranges; and as for my bouquets, they would have stocked a flower-shop. It was quite with difficulty we pushed off at last. Fortunately the tide allowed the admiral's barge to come up to the little jetty, for I am sure if we had started on a palm leaf, as we sometimes did, there would have been disasters and wet feet, to say the least of it. By the time the Euryalus was reached, she was found to be ringed round by boats of all sorts and sizes, and it was quite diffi cult to get first on board and then off. Et vivat!' rang out in great force on every side, and even a tremulous' God-save'; but the hearty thanks and benedictions were the pleasantest sounds. At last the screw turned, and the fine old ship headed once more for the wide ocean. The boats and waving kerchiefs were soon dwarfed into so many dots on the dancing waves, and in an hour or two we had looked our last on Rodrigues. The wind was fair for going back, and the voyage proved quite smooth as well as very pleasant. Ces Messieurs avec les trompettes' discoursed delightful music to us after dinner, and the soft moonlight lasted all the way back. The dear old Euryalus has gone the way of old ships, but has happily left a smart successor to her name and fame. Regular communication (that is to say, as regular as the hurricanes will allow) has been established with Rodrigues, and it must be more prosperous, for I see by the latest returns that the population has doubled itself since that delightful visit. IN THE BYRE. THE warm milk swishes in the pail ; Yet, louder than the hissing spurt, One moment, in the pool of light I raised my eyes; then looked no more; With parted lips and foreheads bright. They passed; and, though I, toiling, bide, Round them with creaking wings and slow; I cross with them the roaring burn; They sink, to watch the bobbing coots Then, as he turns to her the light O big, brown kine within the byre, The prey of passion's prisoned fire. WILFRID WILSON GIBSON. MODERN THEORIES OF LIGHT. Ir must be confessed, I think, that the present aspect of some branches of physical science, as they may be supposed to present themselves to the untrained eye, is calculated to suggest the idea of a troubled sea rather than that of a quiet, cultivated plain; that it must seem to most that in these departments the days of ordered regular progress have passed away, and now the times, though not less productive of facts than those that went before them, are stormy and exciting rather than truly illuminating. And yet this is not really a true picture of the state of things. It only seems so if we choose our standpoint badly. Let me give an illustration. Imagine two people watching an express trainone from the platform of a station through which the train has just rushed, the other from a vantage point a little further distant and a little to one side. What do they see? To the first, as the reader will discover if he tries the experiment, the train seems to move away fitfully; to take a succession of jumps, as it were. The second, on the other hand, forms a truer judgment; to him the movement of the flying train appears even and continuous; he sees none of the stops and starts that the man on the platform believes himself to have detected. And so it is in regard to the progress of the branches of science that are in my mind. If we stand too near, or select our standpoint badly, if we concentrate our gaze on the last discovery, or even on the last few discoveries, much will escape our notice, and we shall form a picture very different from that seen by an observer who secures a wider field of view, so that he perceives whence each new departure starts, and can form an opinion as to what the direction of the next movement is likely to be. In short, if we wish to understand the significance of the discoveries in physics and chemistry that have startled the world during the last few years, we must stand back, as it were, so that we may see them in relation to the events which came before them. We must, in fact, know something of the steps which led up to them, something of the history of the group of facts or ideas to which they belong. VOL. XVI.-NO. 95, N.S. 40 If Dr. Thomas Young could have revisited the famous lecture theatre of the Royal Institution in Albemarle Street, where once he taught, on the evening of Friday, April 19, 1901, when Professor J.J. Thomson was demonstrating the existence of particles a thousand times smaller than atoms of hydrogen which move with velocities comparable with the velocity of light, and if he had been shown how these particles generate light when they fall upon dense obstacles, it seems likely he might have jumped to the conclusion that, after all, the wave theory of light which he had done so much to establish was dethroned, and that the corpuscular theory of Newton was about to reign once again in its stead. And yet one may hazard the guess that Professor Thomson was never more convinced than at that moment of the soundness of the wave theory. The present position of the wave theory of light is not, I think, very difficult to understand if once we get the facts before us in their proper relations; but to those who have not had an opportunity for doing this the whole question of the nature of light must by this time have become very perplexing. They have understood for years that light consists of waves or ripples in something called the ether'; but what is this they hear about the light-producing corpuscles in the radiations of radium, about a new theory which teaches that the Aurora Borealis is produced through the impacts of minute corpuscles shot out by the sun on the earth's atmosphere, and about the light-producing powers of the electrons in the cathode streams of the Crookes' vacuum tube? What have these to do with waves and ether? To get the answer to these questions, let us endeavour to trace the history of the wave theory; let us see how it stands at this moment, and what, if any, is the part played by these corpuscles in the generation of light waves. Before we begin our survey, I must ask my readers to remember that light travels in straight lines with a velocity in air of about 186,000 miles per second. That when a ray of light passing through the air meets a solid object, such as a sheet of silver or glass, it may rebound, as it were, or be reflected, as happens when it falls on a polished silver plate, or may pass through the solid more or less completely, as happens when a light ray falls on a sheet of is turned any transparent solid. That in this latter case the ray out of its original course, refracted, at the surface of the solid, unless it fall upon it at a right angle, and that it is again diverted, only in the opposite sense, when, emerging from the denser medium, |