This brought the study of the cathode rays into prominence, and through the investigations of Professor William Crookes, in 1879 and afterwards, a conclusion was reached that a “Fourth State of Matter” really existed. He perfected tubes of very high vacuum, by means of which he showed that molecules of gas projected from the cathode moved freely and with great velocity among one another, and so bombarded the inner walls of the tube as to render it fluorescent.
Subsequently, Hertz showed that the cathodic rays would penetrate thin sheets of metal placed within the tube or bulb; and soon after, Paul Lenard (1894) demonstrated that the cathodic ray could be investigated as well outside of the tube or bulb as within it. He set an aluminum plate in the glass wall of the bulb opposite the cathode. Though ordinary light could not penetrate the aluminum plate, it was readily pierced by the cathodic rays, to a distance of three inches beyond its outside surface. With these rays, thus freed from their inclosure, he produced the same fluorescent effects as had been noted within the bulb, and even secured some photographic effects. These cathodic rays produced no effect on the eye, which proved their dissimilarity to light. Lenard showed further that the cathodic rays outside of the tube could be deflected from their straight course by a magnet, that they might pass through substances opaque to light, and that in so passing they might cast a shadow of objects less opaque, which shadow could be photographed. Now Professor Roentgen came upon the scene. He had been conducting his experiments in Germany, along the same lines as Lenard, and had reached practically the same results as to the penetrative, fluorescent, and photographic effects of the cathodic rays. But he had gone still further, and, in 1896, fairly set the scientific world aflame with the announcement that all the effects produced by Lenard in the limited space of a few inches could also be produced at long distances from the tube, and with sufficient intensity to depict solid substances within or behind other substances sufficiently solid to be impermeable by light. Professor Roentgen claims that his X ray is different from the cathodic ray of Lenard and others, because it cannot be deflected by a magnet. This claim has given rise to much controversy respecting the real nature of the X ray, a controversy not likely to end soon, yet one full of inspiration to further investigation.
SCIAGRAPH OR SHADOW PICTURE.
By X Ray process.
The essential features of the best approved apparatus designed to produce the X ray and to secure a photograph of an invisible object, are: (1.) A battery or light dynamo as a generator of the electric current, accompanied, of course, by the necessary induction coil, which should be so wound as to give a spark of at least two inches in length in the tube where a picture of a simple object, as a coin in a purse, is desired; a spark of four inches in length where pictures of the bones of the hands, feet, or arms are desired; and a spark of from eight to ten inches in length where inside views of the chest, thighs, or abdomen are desired. (2.) The second essential is the glass tube. The one in common use is the Crookes tube, usually pear-shaped, and resting upon a stand. Into it is inserted two aluminum electrodes or disks, the one through the smaller end of the tube being used as the cathode, and the one from below and near the large end being used as the anode. (3.) A fluoroscope with which to observe the conditions inside the tube necessary to the production of the X ray, to decide upon its proper intensity, and to establish the proper degree of fluorescence. The favorite fluoroscope for this purpose is the one invented by Edison. It is in the form of a stereopticon, in which is a dark chamber after the manner of a camera. In front are two openings, admitting of a view within of both eyes. At the opposite, and greatly enlarged, end is a screen which is rendered fluorescent by means of a new substance (tungstate of calcium) discovered by Mr. Edison after some eighteen hundred experiments. Such is the power of this fluoroscope that it may be used as an independent instrument in cases of minor surgery to locate bullets or other objects buried in the flesh, even before a photograph has been taken. (4.) The photographic plate, which is prepared with a sensitized film and mounted in a frame as in ordinary photography. Upon this film the object to be photographed is laid, say, for instance, the human hand, care being taken to have the film or plate at a proper distance from the Crookes tube. Current is now turned into the tube, the X ray is developed, the film is exposed to its effects, and the result is a negative showing the interior structure of the hand,—the bones or any foreign object therein. This negative is developed as in ordinary photography.
The discovery and application of the X ray has proved of immense value in medicine and surgery. By its means the physician is enabled to carry on far-reaching diagnoses, and to ascertain with certainty the whole internal structure of the human body. Fractures, dislocations, deformities, and diseases of the bones may be located and their character and treatment decided upon. In dentistry, the teeth may be photographed by means of the X ray, even before they come to the surface, and broken fangs and hidden fillings may be located. Foreign objects in the body, as bullets, needles, calculi in the bladder, etc., may be localized, and the surgery necessary for their safe removal greatly simplified. The beating of the heart, movement of the ribs in respiration, and outline of the liver may be exhibited to the eye. It has been boldly suggested that in the X ray will be found an agent capable of destroying the various bacilli which infest the human system, and become germs of such destructive diseases as cholera, yellow fever, typhoid fever, diphtheria, and consumption. Even if this be speculative as yet, there is still room for marvel at the actual results of the discovery of the X ray, and its future study opens a field full of the grandest possibilities.
IX. OTHER ELECTRICAL WONDERS.
The novel idea of keeping time by means of electricity originated quite early in the century, and culminated in two kinds of electric clocks, one moved directly by the electric current, the other moved by weights or springs, but regulated by electricity. The former have the advantage of running a very long time without attention, but as it is impossible to keep up an unvarying electric current, they are not so accurate as the latter in keeping time. Though the latter are popularly called electric clocks, they are really only clocks regulated by electricity, and in such regulation the electric current comes to be a most important agent, as is proved at all centres of astronomical and other observations, as at Greenwich and Washington. At such centres the astronomical time-keeper is set up so as to run as infallibly as possible. This central time-keeper, say at Washington, is electrically connected with other clocks, at observatories, signal-service stations, railway stations, clock-stores, city halls, etc., throughout the country. Should any of these clocks lose or gain the minutest fraction of time as compared with that of the central time-keeper, the electric current corrects such loss or gain, and so keeps all the clocks at a time uniform with one another and with the central one. Electrical devices are also often attached to individual clocks, as those upon city hall towers and in exposed places, for the purpose of meeting and correcting inequalities of time occasioned by weather exposure, expansion and contraction by heat and cold, etc.
The fatherhood of the very useful and elegant arts of electrotyping and electroplating is in dispute. Daniell, while perfecting his battery, noticed that a current of electricity would cause a deposit of copper. In 1831, Jacobi, of St. Petersburg, called attention to the fact that the copper deposited on his plates of copper by galvanic action could be removed in a perfect sheet, which presented in relief, and most accurately, every accidental indentation on the original plates. Following this up, he employed for his battery an engraved copper plate, caused the deposit to be formed upon it, removed the deposit, and found that the engraving was impressed on it in relief, and with sufficient firmness and sharpness to enable him to print from it. Jacobi called his discovery galvanoplasty in the publication of his observations in 1839. It was but a step from this discovery to the application of the electrotyping process to the art of printing. A mould of wax, plaster, or other suitable substance is made of an engraving or of a page of type. This mould is covered with powdered graphite (black lead) so as to make it a conductor of electricity. It is then inserted in a bath containing a solution of sulphate of copper. An electric current is passed through the bath, and the copper is deposited on the mould in sufficient quantity to give it a hard surface capable of offering greater resistance in printing than the types themselves, and also of producing a clearer impression. In electroplating, practically the same principle is employed. The bath is made to contain a solution of water, cyanide of potassium, and whatever metal—gold, silver, platinum, etc.—it is designed to precipitate on the article to be electroplated. The current is then passed through the bath, and the article—spoon, knife, fork, etc.—to be electroplated receives its coating of gold, silver, German silver, platinum, or whatever has been made the third agent in the bath.