IMAGE EVALUATION TEST TARGET (MT-3) 1.0 ^^ ta 121 I.I III ili m lit s; tis, 12.0 u IJi& Hiotographic Sciences Corporation 23 WIST MAIN STMIT WiBSTIR,N.Y. M5S0 (716)t73-4S03 ^ signif^e "A SUIVRE", le symbole V signifie "FIN". Les cartes, planches, tableaux, etc., peuvent dtre film^s d des taux de reduction diff^rents. Lorsque le document est trop grand pour dtre reproduit en un seul clich6, il est film6 d partir de I'angle sup6rieur gauche, de gauche d droite, et de haut en bas, en prenant le nombre d'images ndcessaire. Les diagrammes suivants illustrent la mithode. D 22X 1 2 3 4 5 6 WITH COMPLIMENTS OF . . t \ N A. l> ^ The University of Toronto and The School of Practical Science. Toronto H ROENTGEN RADIATION By J. c. Mclennan. b,a. Assistant Demonstrator in Physics University of Toronto TMI •nvANTPHIIt, TORONTO >0 lAV ■TRfiT '.^; Qt4SI M3 ) ROENTGEN RADIATION BV J. C. McI.KNNAN, B.A., Assistant Deino:;itrat<)r in Physics at Toronto University. When the announcement was recently made l)y Professor Roentgen, of WurzSurg, (lermany, that he had discovered a new kind of radiation, it excited so much popular interest, and seemed to have such a far reaching influence in the development of physical science, that we considered it advisable to verify in Toronto at once, as far as practicable, the results obtained by the original investigator • > 4 r? "* » mm < 'Wfii f t ^' i • . 1 1 {Ft|^^^^^H hORk:^ 1 M ^^^Ki , ,f^ W ,«•« Hy khul penuibsiun of MASSliV i'KHSS. Fie. I. Apparatus showing Induction Coil and Bell-Jar contaitiing Crookes' Tube. Together with Mr. C. H. C. Wright, B.A.Sc, Lecturer in the School of Practical Science, and Mr. J. Keele, B.ASc, of the same institution, the writer repeated these experiments, and found the results exactly as described, and even more wonderful than we had anticipated. ROENTGEN RAtllATION. As shown in the accompanying illustration, the apparatus used by us consisted of an induction coil of moderate size and a Crookes' tube of special form. 11) Ui.ul iiuriuiiMi'ii ui Massi-.v I'kI'.sS. FIQ. II. Noiihwcst Medal Photographed through a Block of Wood. Crookes' tubes are made of glass, and were originally designed to exhibit properties of the electric discharge when passed through air at different pressures. The electric current is led into and from them by means of platinum electrodes sealed into the glass and carrying discs or caps of aluminium of different shapes to give variation to the form of the discharge. When an electric spark is passed through a tube from which the air is being gradually exhausted, it presents a variety of appearances, each being characteristic of the vacuum obtained. At first it consists of a single line of light. It then breaks up into a number of irregular streaks and this appearance, as the exhaustion goes on, gives place to a bluish colored halo between the electrodes. This halo then breaks up into a \ r?3^S»3l»5!5SI!aHe!ta.-5A^ •'SZJeK=.j.:>.^::-^-r ROKNTCEN KADIATION. series of parallel discs, and, on pushing the exhaustion slill further, these disappear entirely from the netjative, but remain in the region of the posi- tive electrode. I fere a new appearance is presented. When the air has been exhausted to this degree, the part of the tube directly opposite the negative electrode bcfjins to glow with a beautiful fluorescence, which indicates that some peculiar invisible discharge, causing this effect, is ema- nating from the negative electrode. It is the cathode rays, so railed, which are said to form this discharge, and the tube in this condition con- stitutes a Crookes' tube. These cathode rays have been very fully investigated by I.enard, Hertz, Thomson, and others. It is found that, like ordinary light rays.' they travel in straight lines, are capable of producing intense heat, and, unless especial care is taken, there is great danger of melting the tube if the discharge is continued without interruption, even" for a few minutes. By kind permission of Massky 1'KKSS. FIG III. Opera Glasses Photographed Through Case. If a magnet is brought up to the tube when these rays are passing they can be readily deflected from their direct path, and, in fact, a finger presented to the tube is suflficient to deflect them towards the point of contact. KOKNIIiKN KArn.MION, In his early experiments, l»rofessor Roent«en found that on surround- ing a Crookes' tulie while in action with a close-fitting black paper cover, it was possible to see in a completely darkened room a brilliant fluorescence upon paper covered with barium platino cyanide held near the tube. This appearance he found to be still visible, though faint, at a distance of two met rs. Krom this expcrimtnt he concluded that the Crookes' tube was the origin of the action causing the fluorescence, and that this action, whatever it was, passed through paper which was impervious to ordmary light. Kvtending his ex[)eriments by placing other substances between the Crookes' tube and the fluorescent screen, he found that all bodies allowed this new kind of radiation to pass through them in a greater or less degree. Wood, paper, and water were very transparent, aluminium and ebonite fairly so, while copper, lead, gold, platinum, and even glass were quite opaque unless made in very thin plates. Difllrent thicknesses of various materials were tried, and the results obtained showed that as the thickness increased the hindrance offered to the new rays by all bodies also increased. The density of bodies seems to be the only property which aflecis their permeability, and yet their densities alone do not determine com- pletely their trans[)arency, as plates of aluminium, glass, cjuartz and Iceland spar of e(pial thickness were interposed between the tube and the screen, and it waij (piite evident that, although their densities are about the same, the resistances they off'ercd to the passage of the rays were ([uite different. Although these new rays can be passed through many substances which are opaque to sunlight, no evidence has yet been obtained which would show that they can be refracted. On passing them through prisms, or lenses, of water, carbon bisulphide, eboniie, aluminium or wood, there is no indication, or, if any, but slight, of refraction at these surfaces. Since many metals and glass of ordinary thickness are found lo be im|)ermeable to these rays, it is but natural to expect that these substances would reflect them ; but all experiments so far stem to show that the oidinary law of reflection does not hold for these new rays, and that if they can l)e reflected at all it is only in a very general and irregular manner. Although this unknown radiation was at first detected and studied by means of a fluorescent screen, it was soon found that ordinary photo- graphic dry plates were sensitive to it, and it is owing to the developments in this direction that such intense interest has been aroused The reproductions illustrating this article are from photographs taken in the course of our own investigations, and they will indicate some of ROKNTC.KM H.\OI\TIOfl. ihe possibilities of the new discovery. Fig. II. wa« oblaineil by placing on the cardboard box containing' the sensitized plate a silvci medal, over which was jjlacel a block of wood one inch thick. The screws also shown in the picture* were driven into the wood, and from the appearance of the FIO. IV. /nslriimciils Pholos;ra[ih u Thtounh Chh: cut it is (juite evidint that while the wood offjred but lillle resistance to the passage of the rays the melals were quite opacjue. Fig III. repre- sents a pair of opera glasses taken in their case. The metal parts were of aluminium, and it can be seen that, while the rays passed through the tubes at all points, they did so to a much greater extent where there was only one thickness of the iiitlal. I'he objtct lenses are clearly defined, showing that the glass is quite opaque, and the outlines of the kCtKNU'.KN KAIIIATlnN. irawing case are indicated but faintly. Kig. IV. shows a stt nients inclosed in a thick leather case. The action u|)on the sensitized Olin of the dry plate seems to he the same as that due to the liKl.t of the sun. The developers used were nietol, hydro(iuinone, pyrogallic acid, and oxalate of potash and iron Tyro' developer seemed to give best results. The images came up rather more slowly than with ordinary light, and the density as seen before fixing the plate was somewhat misie.iding, as the chenncal action seems to be connned to the surface of the film only. The color of the deposit upon the plate by the various developers is the same as that given by sunlight- \anous types of dry plates were tested, but, though we were unable to detect any difTerence in the action upon them, it may be possible, when more properties of the new radiation are known, to produce a more sensi- tive film than those now in use. During our early experiments we found that the tinie reciuired to obtam good impressions on a plate was so long tiiat the utility of the new- discovery seemed to be very limited, even if not doubtful. We therefore directed our efforts to reducing, if possible, the time of exposure, and this we succeeded in doing to a very marked degree. On making a careful test of all the lubes in the Thysicil Laboraloiy, we found one which gave a much stronger radiation than any of the others. This tube, constructed by Scguy, of I'aris, was penr shni)ed, and as It had one electrode inseited in the smaller end, and the other in the side, we were ab'e, by making the formtr the negative terminal, to obtain a large glass surface exposed to the action of the cathode rays. This lube was employed in all our later experiments. Thinking that probably the action would vary with different sensitized films, we conducted a series of tests to determine the relative sensitiveness to the rays of various types of plates, but observed no marked difference, and concluded that any reduc- tion in the time of exposure must be otherwise obtained. As experiments made with prisms and lenses of wood, pilch, and other materials, gave no indication cf refraction at their surfaces, the only remaining method for the concentration of the rays seemed to be an application of the principle of reflection. In order to determine whether the rays could be reflected, a surface of clean mercury was prepared, and it ivas found that when the raj's uy some action coming from the mercuty. To test this apparent reflection still further, a sensitized film, protected by a plate- holder, was placed at a distance of about tivenfy centimetres bclaiv the Crookes' tube. A thick plate of glass was then inserted midway between the '. Mi^.'BlTat'wm-y K0KNT(;KN RAl»IAiION. 7 tubt and thejilni, parallel with the latter, with the intention 0/ screening the plate in part from the action of the rays. The tube was then excited for some time, and on dtvelopini^ the film it wjs Joiind that the rays evidently travelled in straight lines, since the part of the film protected by the ,i,'lass plate 7t