chapter 6 (New York: Doubleday, Page & Co.).

CHEMISTRY AND PHYSICS: Smokeless Powders.

"In recent years smokeless powders have largely superseded all others. These contain usually nitro-cellulose (gun cotton), or nitro-glycerine, or both, made up into a plastic, coherent, and homogeneous compound of a gluey nature, and fashioned into horn-like sticks or rods by being forced under pressure, through a die plate having small holes, through which the plastic material is strained into strings like macaroni, or else is molded into tablets, pellets, or grains of cubical shape. Prominent among those who have contributed to this art are the names of Turpin, Abel and Dewar, Nobel, Maxim, Munroe, Du Pont, Bernadou and others. In the recent years of the Nineteenth Century great activity has been manifest in this field of invention. In the United States more than 600 different patents have been granted for explosives, the larger portion of them being for nitro-compounds which partake in a greater or less degree of the qualities of gun cotton or nitro-glycerine."

_E. W. Byrn, Progress of Invention in the 19th Century, page 419._

CHEMISTRY AND PHYSICS: X Rays. The Discovery of Professor Rontgen.

"Fresh proofs await us of the supreme rank of both electricity and photography as resources of art and science as we observe the transcendent powers evoked by their union. From this union no issue is more extraordinary, more weighty with meaning and promise, than the X-ray pictures due to Professor Wilhelm Konrad Rontgen. In these pictures he has but crowned labours which began when Sir John Herschel noticed that a peculiar blue light was diffused from a perfectly colourless solution of quinine sulphate. Professor (now Sir) George Stokes explained the phenomenon by showing that this blue light consists of vibrations originally too rapid to be visible, which are slowed down within the limits of perceptibility as they pass through the liquid. …

"One path of approach to the achievement of Professor Röntgen was opened by Sir John Herschel; another, as important, was blazed and broadened by Professor (now Sir) William Crookes. In 1874 and 1875 he was engaged upon the researches which gave the world the radiometer, the tiny mill whose vanes rotate with rays of light or heat. The action of this mill depends upon its being placed in a glass bulb almost vacuous. When such a bulb incloses rubies, bits of phenakite, or other suitable objects, and electrical discharges are directed upon them, they glow with the most brilliant luminescence known to art. Excited by a cathode ray, that is, a ray from the negative pole of an electrical machine, a Crookes bulb itself shines with a vivid golden green ray which reminds the onlooker of the fluorescence of earlier experiments. … "Year by year the list of substances excitable to luminosity in a Crookes bulb has been lengthened, and in 1894 it was the good fortune of Professor Philipp Lenard to discover a wonderful power of such a bulb. Emerging from it was a cathode ray which passed nearly as freely through a thin plate of aluminium as common sunshine does through a pane of glass. Hertz had, a few years previously, discovered that metals in very thin sheets were virtually transparent (or, to use Mr. Hyndman's term, transradiable) to his electric waves. This property was found by Professor Lenard to extend to the cathode ray and in a much higher degree. … The ultra-violet ray of ordinary light has the singular power of causing the gases which it may traverse to become conductors of electricity, with the effect of discharging an electrified metallic plate; this property is shared by cathode rays. Associated with them are the rays of still more extraordinary powers, discovered by Professor Röntgen. In his own words let his achievement be recounted, as published in 'McClure's Magazine,' April, 1896.

"'I have been for a long time interested in the problem of the cathode rays from a vacuum tube as studied by Hertz and Lenard. I had followed their and other researches with great interest, and determined, us soon as I had the time, to make some researches of my own. This time I found at the close of last October. I had been at work for some days when I discovered something new.' 'What was the date?' 'The 8th of November.' 'And what was the discovery?' 'I was working with a Crookes tube covered by a shield of black cardboard. A piece of barium platino-cyanide paper lay on the bench there. I had been passing a current through the tube, and I noticed a peculiar black line across the paper.' 'What of that?' 'The effect was one which could only be produced, in ordinary parlance, by the passage of light. No light could come from the tube, because the shield which covered it was impervious to any light known, even that of the electric arc.' 'And what did you think?' 'I did not think; I investigated. I assumed that the effect must have come from the tube, since its character indicated that it could come from nowhere else. I tested it. In a few minutes there was no doubt about it. Rays were coming from the tube which had a luminescent effect upon the paper. {437} I tried it successfully at greater and greater distances, even at two metres. It seemed at first a new kind of invisible light. It was clearly something new, something unrecorded.' 'Is it light?' 'No.' 'Is it electricity?' 'Not in any known form.' 'What is it?' 'I don't know.' And the discoverer of the X rays thus stated as calmly his ignorance of their essence as has everybody else who has written on the phenomena thus far.

"'Having discovered the existence of a new kind of rays, I of course began to investigate what they would do.' He took up a series of cabinet-sized photographs. 'It soon appeared from tests that the rays had penetrative power to a degree hitherto unknown. They penetrated paper, wood, and cloth with ease; and the thickness of the substance made no perceptible difference, within reasonable limits.' He showed photographs of a box of laboratory weights of platinum, aluminium, and brass, they and the brass hinges all having been photographed from a closed box, without any indication of the box. Also a photograph of a coil of fine wire, wound on a wooden spool, the wire having been photographed and the wood omitted.

"'The rays,' he continued, 'passed through all the metals tested, with a facility varying, roughly speaking, with the density of the metal. These phenomena I have discussed carefully in my report to the Würzburg Society, and you will find all the technical results therein stated.' He showed a photograph of a small sheet of zinc. This was composed of smaller plates soldered laterally with solders of different metallic proportions. The differing lines of shadow caused by the difference in the solders were visible evidence that a new means of detecting flaws and chemical variations in metals had been found. A photograph of a compass showed the needle and dial taken through the closed brass cover. The markings of the dial were in red metallic paint, and thus interfered with the rays, and were reproduced. 'Since the rays had this great penetrative power, it seemed natural that they should penetrate flesh, and so it proved in photographing the hand, as I showed you.'" …

"Provided with a Röntgen bulb, the photographer passes from the exterior to the interior of an object, almost as if he were a sorcerer with power to transmute all things to glass. Equipped with a simple X-ray apparatus, dislocations and fractures are detected by the surgeon, diseases of bones are studied, and shot, needles, and bits of glass or corroding wire within the muscles of a patient are located with exactitude. Thanks to the work of Mr. Mackenzie Davidson, the like detection of renal calculi can be looked forward to with a fair degree of certainty. The same means of exploration offers equal aid to medicine: it demonstrates the calcification of arteries, and aneurysms of the heart or of the first part of the aorta; with improved methods it may be possible to study fatty degenerations of the arteries and larger blood-vessels. Dr. C. M. Mouillin, addressing the Röntgen Society of London as its president, states that the fluorescent screen has now reached such a degree of perfection that the minutest movement of the heart and lungs, and the least change in the action of the diaphragm, can be watched and studied at leisure in the living subject. He considers it probable that the examination of a patient's chest with this screen may become as much a matter of common routine as with the stethoscope to-day. …

"Manifestly, the unseen universe which enfolds us is steadily being brought to the light of day. The investigations of Hertz established that the light-waves which affect the eye are but one octave in a gamut which sweeps indefinitely far both above and below them. In his hands, as in those of Joseph Henry long before, electric waves found their way through the walls and floors of a house; in the Marconi telegraph these waves pass through the earth or a fog, a mist or a rain-storm, with little or no hindrance. What does all this mean? Nothing less than that, given its accordant ray, any substance whatever is permeable, and that, therefore, to communicate between any two places in the universe is simply a question of providing the right means."

_G. Iles, Flame, Electricity and the Camera,