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CAl.LENDAE, M.A, Profes.-ors of Physics, McGill University, Montreal. • «•, !• t I • ••' • • • • • . • • • « • • •• . • • • , • •• • • • •• • ; 4f ■♦" • SwrioN III., 181)(). ' [171] • 'Trans. U.S. C. XI. — Some Exfnritnenta on the JC-Rays. By JOHN Cox, M.A., .vni> IIuoii L. Cai.lkndar, M.A. Professors of Phy.sicH, Mc(Jlll University. Montrciil, (Heiid .May 2S, ISlKi.) A few (lays iifter the iirrival of the news of Riiiit^tMi's discovery, on Feb. 7th. the tirst iipplieation of tlie inethod to suri^ery in the McDonald Physics Huihling, was made hy the jtliotographic locatio'i of a hullet in the leg by Professor Co.x. This jdiotogiaph, together with another of a hand, taken by Messrs. King and Pitcher on the same day, has V)eon described and ligured in the ^rontreai j\ledical .foun.;'! for .Nfarch, 1S!)(). The tube used for taking this photograjjli was the phosphorescent lamp tube of Puluj, which has been widely used in Germany for the same purpose. Out of a collection of upwardsof tifty C"ookes tubes, obtained from Messrs. Geissler in 1804, this tube alone was found to retain a sufli- ciontly i^erfect vacuum ibr the pui-pose of X-ray photography. The exposure recjuircd in the case of the hand was 4;") minutes at a distance of 8 inches. Some of the other tubes were Ibund to give faint results, but they were too weak to be of any ])ractical use. Shortly afterwards we received a copy of Nature, of .Ian. 2;}rd, containing an account of some ex])erimenis by Swinlon, who stated that much better results could be obtained by the use of the Tesla coil oscil- lating discharge. t)n trying this method, we found that several of the tubes in which the vacuum was bad, gave much brighter fluorescence than with the Ruhmkortf discharge, but the detinition of the shadows with any of the ordiiuiry tubes' ^as inferior owing to the doulile kathode. We also found !hat the oscillating discharge had a very marked tendency to perforate the tubes. Several of our Geissler tul>es were tem])orarily damaged in this way, with the oscillating discharge, whereas we had no Huch mishap with the direct discharge, although using a ten-inch spark. With a view of overcoming these and other ditiiculties, upwards of .30 tubes of ditt'erent patterns were devised and constructed by Professor Callendar„bolh for the direct and the oscillating discharge. Incidentally a number of anatomical and other photographs, including several surg- ical cases, were taken with these tubes, and most of the experiments of Rontgen and other observers were repeatetl and veritied. Thef.e obser- vations Avero interesting at a time when scmie physicists imagir.od that the rays proceeded from the anode, or that they could be concentrated and brought to a focus by a glass bell-jar, but the main facts with regard to the X-rays are now so firmly established as to need no further corro- - . 1 . . 55966 172 ROYAL SOCIETY OF CANADA l)oratit>ii oi' tliiw kind. Wo ultirnaloly ahiiiidomMi the uso ol tlic oscillut- iri/:? (iiHcliargo, an wc louiul that wilh tlio direct dis('iiari,'o a greater urnount of power could lie cm]>loyo(l, and moi-o brilliani oH'ocIs Hociirod, without risk of perforating the tube. Tlie one-electrode method of Tesla, though attended witii lews risk of pertbration, appeared to require u very extravagant expenditure of jutwer. The tubes in which the kathode rays were nUowed to impinge on tiio glass whIIh were liuhle to a sei'ious defect. If the X radiating surface won' largo, as in the inaltese cross tube of Crookes, a large; volume of rays could be ])i'oduced. giving brilliant etfccts, and readily visible through the human body, but permitting very poor detiiiition. Jfon the other hand, the glass surface were made small, in order tti secure good dotii\ition, very little jiower couKl bo a))plied without melting the glass. Aluminum windows were tried, following Hiintgen, but could not be made |iermancntly air tight. Such devices as the use of a continuous air-blast, or of oil or water for coolin<-- the tube, besides bcinir trouble- some, wei*o open to obvious objections, All these ditticulties wtn-e met by the discovery of the '• Focus Tube." Apjilicdtion of ike Focus Tulic. — The use of the focus tube represents the greatest i»ractical advance which has boon made on the method of Rontgen. The tube is one of the usual Crookes series, in which the kathode rays are concentrated by means of a concave electrode on a plate of platinum. It is generally used to illustrate the production of heat by the kathode rays, it was discovered that this focus was a very powerful source of X-rays, which ])roceedod in straight lines through the glass, and were capable of casting very sharp shadows, since they pro- ceeded from a very small focal point. We found the first illustration of this tube, as applied to X-ray work, in the British Medical Journal, of March 21, 18!)6. We were fortunate in possessing a very fine focus tube, with a bulb five inches in diameter, and a very large concave electrode. The tube was opened, and the platinum plate bent at a more convenient angle, and the tube then sealed and re-exhausted. The results wore found to be far superior in clearness and density to any of those obtained with the glass tube. The original platinum ]ilate, however, was so thin that a hole was melted through it. The limit of power which can be ap]ilied to these tubes depends on the size and thickness of the platinum plate. The larger and thicker the ])late, the greater the power that can be dissi- pated without overheating the plate and spoiling the tube. With our particular coil and tube, the limit appears to be between fiO and 70 watts on the primary. The stage of greatest X-ray efficiency is a little beyond the stage of greatest heat jiroduction. Method of Exhausting Tubes. — The method which we adopted for exhausting the tubes may perhaps be worth mentioning, as we found it loox A cai-lkndak] experiments ON THE X-KAYS 173 to bo very oxi)oditi()UH, and it does not ii])|)oar to bo gcntM-iilly known or einpl'oyod. On tirHl oxbansling ii lubo, llio cdiiof ditliciilty is ifcrioriilly to got rid of tbt^ lust truces ol" gas from tlio t^lootrodos und tbc wails of tlip tuijo wlion liigli vacua aro ro(iuir('d ibr X-ray worl<. II' tliis gas is not thoroughly removed, the vacuum is liable* to subsequent deterioration. The method which we ado])ted for this purpose consisted in maintaining a continuous discharge througii the tube, during the process of exhaus- tion, by meauH of an alti'innfliuj current applied to the induction coil, the strength ot the current being so regulated as to heat the electrodes of the tube as much as ])Ossible without melting them or causing a deposit on the glass. The effect ol' the current was simultaneously to heu^ the walls of the tube sullicientl}' to dry them very completely without any risk of cracking the glass, as may often happen if the tube is artiticially heated by means of a Hunsen tiame. Starting with a live inch bulb, wet and dirty from the bl()W])ipe, we weri* able in this manner to raise it to an X-ray vacuum in irom half an hour to an hour. The pump which we generally used for exhausting the tubes, was a five-fall Sprengcl of (iermau make, which had been fitted in the labora- toiy with a vacuum trap for drying the mercury, and with an aulonuitic arrangement for returning the mercury to tlie upper reservoir. At its maximum rate of working, this pumj) took only ten or fifteen minutes to raise a five inch bulb from one millimetre to a 8})arkle8s vacuum, if the electrodes had been previously freed from gas by the method above described. Wc found it preferable to the (ieissler form of mercury pump, as it permitted the vacuum to be varied continuouslij, and to be maintained at any desired point. We also used, on several occasions, an automatic Geissler pump of the Max Stuhl pattern. P/icnomend presented by the Focus Tube. — The phenomena jiresented by this tube in action, have frequently been described, but the i)ublished descriptions do not altogether agree with our experience. According to one account which we received, the kathode rays vpero regularl}' I'cflected in a small pencil from the platinum i^late, and formed a minute focus jtoint on the glass, from which the X-rays proceeded. On exhaust- ing our focus bulb for the first time, we found on the contrary that a whole hemisphere of the glass surface on the side expo.sed to the kathod . rays reflected from the platinum, became brilliantly and almost uniformly phosphorescent. We furthei- verified, by taking a pin-hole photograph, that practically the whole of the X-radiation came from the focus point on the platinum plate, and passed directly through the glass without further diffusion. According to a statement by Professor Lodge, which wo observed at a subsequent date, the X-radiation is rendered more brilliant by connecting the platinum plate to the anode, and is diminished in intensity by allowing the plate to bocome red hot. We have not been able to observe these effects, and are inclined to attribute them to change in the vacuum, or to some other peculiarity in the tubes used by Lodge. 174 KOYAL SOCIETY OF CANADA Wf Imvo roiiiiil il a imitlcr of /^rt-iit imporiunci^ lor olttuinirm clciir luid Itnlliunt pliotoi^raphs. t<) n-movt^ tlio UmihI tmt'cof water viipoui* from > tim tul)c. 'riuf prOMcnco of waltT vapour has {\h' ott'oct of niakinj^ tho locus point inucli less sharp, ami llu! sparUinn- vci-y irn-i^uhir. 'flic phos- phori'Hct'iici' ot' tlio yhisK is luucli loss lirilliant, wit h occasional sectorial flashes from tho hack of the kathode. Shadows of boncts on the (luoros- cope are much less cleai'y defined, and appear to he nearly uh transparent as the flesh. If much wiiter vapour is present, the platinum plato a|>pears to he more hiu:hly heated for the same power, than if the air in the tuhe is dry. The vacuum at tho sparkiiii;- limit, appears to In- niu(di higher, as measured by the \[cLi'Od giui^i!. •(102 to (1(15 mm. as com]»are(l with 010 to'O.'id niu). for dry air. but these fif^ures, owins;; to the extreme slowness of difl'usion. and the al)sor|>tion of wulei" va]»our by the phos- jdioric anhydride in the ])um|). do not lu-ce.ssarily represent the actual vacuum existing in the tiihe. That these effects are to be attributed to tho ])re8enco of water vajtour, is i-endered |(r<>hablt! by tlu( fact that they are always observed on exhaustini^ a new tid)e, if ])recautions have not been taken to dry it, and that they disappear if a small (|uantity of dry air if, admitted and the tube re-exhausted. The presence of water nuiy also be verified by spectroscopic observations. We have observed these apjjoarances in X-ray tubes of various makers. 1'hey ha /e ijenerally been ex]>Iained by othci'ctbservers as beinu; due to X rays o'. ilifl'eivnt kiiuls. or to different degrees of vacuum, or to dilfei'ont kinds of dischari^e. No doubt these explanatioi\s are often true. An increase in the vacuum certainly incx'eases the relative trans- pai'ency of tho bones, and the effects are often considerably modified by any change in the character of the discharge. Hut so far as our exper- iments go, the ]»resence of water vapour is a much more serious source of disturbance, and afl'ords in many eases a much more likely explanation of the irregularities. Method of Operating. — For the sake of mo •• completel}' investi- gating the effects with different gases, and imder different conditions, we havi' preferred to keejj the tube permanently connected with the pum|). Incidentally this method ])ossessesthe advantage that it is possible to work tho tube continuously at its point of highest efticiency for anj' length of time. With a good vacunr. and a powerful discharge, the air in the tube a])pears to get used up .so i ipidly that the spark soon refuses to pass otherwise than outsitle the tube. With a sealed tube, it is generally necessary to stop at intervals and warm tho tube. We found it prefer- able, however, to supply small (quantities of dry air occasionally through a tap connected with the j)ump. On one occasion, the tube was operated almost continuously in this numner for nearly two hours, including one exposure of over an hour without any intermission. The admission of air was so adjusted that tho discharge took an alternative path by a six [cox .MAi.LENDAii] EXl'KKI M KNTS ON TIIK X-RAYS 17S inch ^ap in air once in ovoiy five or ten .IIhcIi arises. It was not possiitie t(t keep (lie proportion (initc constant. Iiiit a very lair avcraijc was main- tained. A little air was admitted every one oi- two minutes. The character of the dischari^e. and the X-rudiation appeurod to lie nearly unchanged ihrou^^liout. The inttmsity was, W anythiti" greater at the end of the exposure. At t hc! end of tli«' exposure. Iiowi the pressure of the air in tlie luhe was found to have increased to n. • the same extent as if the air admitted to the tulie had all accumulated in the fuhe, and lui'l not lieen used up hy the diHciuirii;e or occluded hy the walls as is generally suppo.s(>d. Thin would ajtpear to imply that the production of kathodes rays is due in part at least to sdine change in the constitution of the jL^as in the tuhe, and is not meroly a (luestioii of the de,i;;reeof vacuum. After allowing the tube to rest for three hours, the vacuum vvan found to lie almost unchani^etl. hut no kathode rays were produced until the dis(diarife had Imh'u jiassed for neai'ly a <[uartei' of an hour. Similar j>henomena w.-re olisiM'ved on other occasions after prol()ni;ed i-xposiircs. Jt is p!ati'H wliich wo tlrHt UHtMl. Stanley, HcnHilomotoi' 50, H|)pc>ai' to ^ivo ivsultH which from all accountN were at loant «m|UuI to those which wery |)r()loni^iii^ the exposure lu'voiid \i'M minutes or a (iiuirti^:* of an hour. A longer expo- sure appeared togivo i> llivt ovor-exposed result, in which the fuintur biing out slight ditlcrenees of density which wore otherwise loo faint lo be ajtpreeiateil. The X-ray photograph dill'ers from that produced by <o- suro might bo enormously roducud if it were possible to discovcu- a sensi- tive tilm capable of absorbing tho whole onorgy of the X-radiation in a singhi thickness. Son)e advertisers claim to have reduced tho lime tt) less than one-bund I'cdih in this nuinncr, but .so far as we can discover their results do not ai>i'car to bj in any way yuporior to tho.se which wo have obtaineil with oruiiuiry plates. Stereoscopic X-Jiaij Phutoyriipha.— ln locating a small object in tho thicker parts of the body, it is often nect^ssary to know the diiplii at which it is situated. \'arious more or less compli(tatod methods liave boon proposed for ace()m[)lishing this. Tho majority of tho proposed methods turn on securing a pair of photographs cither taken in dilferent directions, so that the coordiiuites of the object jnay be deduced, or else taken 'Vom slightly ver the umbilicus. Two expo- ures of ten minutes each were given on the same plato, and the tubo was shifted an inch and a half between tho two, in a horizontal direction. The patient was lying on his back on the plate, which vvas at a distance of abovit 20 inches from the focus. The shadows of tho ])elvi8 and oLher bones all show sharp and double edges. The shadows of the fine copper ring, cast through the viscera and si)ine, at a distaiice of eight inches from tlie plate, are so sharp that the diameter of the wire can bo measured. The pin, however, was not found on the plate ; either because it was not there, x)r because it was kept moving by the respiration or the peristaltic action of the intestines. Maynetic Experiments. — The only certain jtoint of difference in kind at present rocognized as existing between the kathode rays as investigated by Lenard and the X-vays of Eontgen, is that the latter are not deflected by a magnet to any aj)preciablo extent. The Rihitgon rays far surpass tho Lenard rays in point of penetrative power, but the difterence her- is one of degi'oe only. Accoi'ding to Lenard, kathode rays differing in inten- sity, according to the degree of vacuum, iliffer also in their penetrative power, and in the extent to which they are deflected by a magnet. It appeared, therefore, quite a tenable hypothesis that the X-rays wore really of the same nature ])reeisely as the kathode rays, but that they consisted of that part only of the kathode radiation which was able to survive reflection from the platinum plate and transmission through the glass, and were consequently less liable to subsequent absorption or deflection. With our focus tube (owing to the care taken in adjusting the platinum plate, and the consequent minuteness of the focus point, which was less than two milimetres in diameter), we were able to obtain ex- tremely sharp shadows at a considerable distance from the tube and the object casting the shadow. It was therefore easy to verify the statement of Rontgen to a higli degree of accuracy. We also attempted to rfepro- duce tho ex]>eriment of Lafay, who states that ho obtained a deflection of the X-rays if they were passed through an electrified plate. Wo did not, however, succeed in obtaining any positive evidence of such an effect. It occurred to us that the X-rays might be more amenable to magnetic deflection in a vacuum than in air outside the tube. With this idea wo tried the effect of approaching the magnet very close to the tube with the direction of its lines of force tangential to che boundary of tho IcoxACALLMNDAKj KXPPnilMENTS ON THE X-RAYS 179 intense groon fluoreHconco covering one Imlf of tho walls of tho tube on the sidooxpoHtHl to the roHoction from tlic ])liitiniim pluto. Tlu' boundaiy of this green fluorescence was observed to bulge in or out according to the direction in which, the magnet Avas presented, precise!}' as if caused by rays having the same properties as ordinary kathode ri'.ys, although proceeding fi'om the platinum plate, and not direct from tiie kathode. On making simultaneous observations with the fluoroscope and with tho photographic plate, wo found that the boundary of the X-radiation out- side the tube, which under ordinary conditions coincides exactly with the plane of the platiiuim plate, was also deflected by the magnet, but in tho opposite direction to the boundary of the green fluorescence. This ett'ect was verifled on several occasions in various ways, the deflection amounting in some cases to half an inch on the photographic plate at a distance of eight inches from the tube. We conclude from these observations that the rays causing tho brilliant green fluorescence of the glass, were probably identical with ordinary kathode rays, and were reflected by the platinum according to the same law of difl'uso reflection as the X-rays. This observation is of some interest as establishing a point of .similarity between the X-rays and kathode rays. The other observation would however ap])ear to show that the two are distinct. The fact that the boundary of the X-radi- ation appeared to be deflected, is probably to be explained by a slight shift of the focus point on the platinum jilate, which was not perfectly plane. This explanation receives support from the fact that the shadow of the magnet itself as seen in the same photographs, is not perceptibly double. Further, the sharpness of the boundary both before and after deflection in each case, would appear to lend support to the view that the kathode and X-rays are of two distinct kinds, sharply separated in properties, rather than rays of the same kind, (littering only in degree, and connected by a continuous .series po.s.sessing intei-mediate projierties In the way of jienetration and magnetic refrangibility. We might, there- fore, still suppose the kathode rays to bo streams of radiant atoms, even if the X-raj's were proved to be of the nature of a wave motion in the a>ther. Action of uY'-Rays on Selenium. — Among the negative results which we obtained, there are some perhaps which deserve mention. A selenium cell was prepared by Professor Cox, consisting of copjier wire wound on a plate of mica, and annealed in the usual way. The resistance of the film, when measured with a megohm and a Thomson -Variey slide box, was found to be nearly ten megohms. This somewhat high value was probably due to the thickness and small size of the selenium film. It proved, however, to be veiy fairly sensitive to ordinary light, and, what was more important, to have an extremely constant resistance, and to return very quickly to the original value when the disturbing influence 180 ROYAL SOCIETY OF CANADA was removed. With (ho galvunoinetei- which wo used, u light of ono candle power at a distance of one metro was found to give a doHection of thirty scale divisions. The deflections wore so con.sistent that iho cell would have niado a very fair photometer. The batter}' used was a singla cell of a silver chloride testing i>at(ery, and the variations of resistance Avero observed by the bridge method using the slide box and wire megohm. The same selenium cell was ex])0sed at a distance of three inches from the tube to the most jiowerfiU X-radiation which we could ])roduce, but no etlect whatever could be observed. The sensitiveness to light was tested both before and after exposure several times, but no change could be detected. It may be necessary to remark tluit the selenium was pro- tected from the light and from the electric discharge by a double thickness of one-mil aluminum foil, which though absolutely opaque to light, did not cast a perceptible shadow on the tluoro.scope when tested by the X- rays. The scrcoii of foil was connected to oaitli and to one polo of the galvanometer. It is necessary to emphasise these precautions as it appears that other observers have obtained ])0sitive results by neglecting them. The galvanometer which we used v/^as adjusted to give a deflection of 1 scale division for 1 volt through 50,000 megohms. It had a resis- tance of 110,000 ohms, and a ])eriod of 15 seconds. Eicctrostatic effects of the X Rays — Within a short time of the publication of Eiintgen's discovery, it was shown by J. J. Thomson that the X-rays possesseil the same [)roperties as the kathode raj's of Lenard, of discharging an electroscope, however, carefully insulated. He expressed this result by saying that any substance through which the X- ra3's passed, was rendered for the time a partial conductor. Tlie beha- viour of paraffin wax in particular was given as an instance of this etfect. The time of discharge of an electroscope or of a small condenser has been suggested as a means of measuring the intensity of the X-radiation at various distances and under various conditions. Some very surpris- ingly exact proofs of (he law of the inverse squai-e were obtained in this manner by some French physicists. It appeared from some of our photograj)hs, that the X-rays were not ditfused from the platinum plate according to the same law as obtains in the case of the diffuse i-etlection of ordinary light. We endeavoured to use the discharge method for measuring .the intensity of the rays diffused in different directions. We found, however, that it was not possible to operate the tube at a perfectly constant intensity, and the rate of dis- charge itself did not appear to be always uniform oven if there were no apparent change in the tube. It therefore occurred to us to try whether with a very sensitive galvanometer the leakage current itself might not be directly observed. Kor this purpo.se wo constructed small condensers of very thin aluminium foil and paraffined paper. The foil was so thin rcx)X A cAU.BNUAR] EXPERIMENTS ON THE X-RAYS 181 that ll>e X-i'iays wore ublo to i)enetrate a thickness of a quarter of an inch of condenser with little absorption. We hoped in this manner to be able to obtain readings with greater rai)idity and accuracy, and also to bo able to u?o a balance method for com])aring the intensities of the radiation in different directions simultaneously. The condensers thus made were inclosed in a screen of aluminium foil connected to earth, in order to protect the galvanometfir from the direct otfccLof tho electrification due to the discharge. Four condensers . were made of different sizes and capacities. Some trouble was expe- rienced at first in making the leakage sufliciently small. When this difficulty was overcome, and asnuiU ccjudenser had been made of suitable capacity and sufficiently free from leakage, it was found that tho effect to be observed, although measui-able, was very transient. The X-rays apparently did not render the dielectric a conductor so long as they were passing through it, but produced only a temporary effect ecjuivi-lent to an absor])tion cur»_i-t. AV^e did not, however, determine whet'.ier the * ■ , absorption were actually increased by the incidence of the raj's, our main object being to test a method of measurement of the intensity of the rays, ,3 which the experiment proved to be impracticable, or at least to have no advantages over the electrometer methoil. Absorption of X-Iiaija by Li, !* ■ material of an organic nature. The absorption was considerably increased by the presence of acids or salts, in proportion to the strength (jf the solution. The opacity did not appear to depend upon the electrical conductivity, but rather on the atomic weight of the metallic constituent of the salt. For instance, a 182 ROYAL SOCIETY OF CANADA woaU I'dlution of copix'i" Hul|ihiilo wiis imieli inoro o|mquo thiin ii similar Holulioii of Hiilpliiii'ic acid, allhoii^h Iho conductivily of llii' co|)|)er suipliatc was imicii Ichs. In no case could wo dotoet any ovidence ol any ditlusion of the rays an by pasisai^o tliroui;li a tiivliid nicdium. The kathode rays investigated l»y Lonard showed this elfeel of dill'usion in a very marked manner in atmospheric air. Some ohservers have stated that tliey found the same oft'ect with the X-rays, ft is po.ssible that an etVoct of this kind might be found in the case of a fluorescent liquid. The rays in their passage through the liquid, certainly ap])eare(l to undergo a kind of tiltering process. In passing through the last milli- metre of the .solution, a much smaller proportion of the surviving rays wore absorbed than in the first millimetre. The weakening of the I'ays was, however, much more i-apid than in simple proportion to the thick- ness. Doubling the thickness of the layer in all cases a])peared to diminish the intensity by much nu)re than half, but the ratio of reduction a|)pearcd to vary to some extent, according to the intensity of the source as well as the thickness of the layei-s considered. Vclocifi/ of the A'-/i!^///.s.— AVe made someractically a negative result, like the result of so many other experi- ments on these rays, but it may be of value so far as it goes. Since the X-rays are not amenable to reflection or refraction, the problem is not capable of so complete a solution as in the case of light. The only ]iro])erty, in fact, w'lich we were able to use for the purjiose of the experiment, was that of alisorption by a metallic screen. The method adopted was somewhat analog.- to that used by Fizeau in the case of light, but with certain modifications necessitated by the different proper- ties of the rays. The rays were made to pass between the teeth of two rapidly revol- ving wheels fixed on a rigid axis at a distance of a metre apart. If the time occupied by the rays in traversing the distance between the wheels wei-e an appreciable fraction of the time of one revolution of the wheels, certain aberration effects would evidently bo introduced, the magnitude of which would depend upon the velocity of the rays. We were restricted to a distance of the order of a metre, both on account of the necessary lightness and rigidity of the connecting shaft, and because of the impossibility of obtaining a parallel beam of rays which could be transmitted over greater distances without too great a loss of intensity. The wheels were made nearly a metre in circumference, and we found ii possible to drive them at a speed of 25 revolutions per second without; [oox 4 CAttENDAR] EXPER%.IENT.S OxI THE X-RAYS , 183 apprtjciablo vibration. Assi. ming that it would 1k' possible to observo an aberration displaconu'nl of ono-tiitb of a niillini. on tlio cirt-uniforoncu, wc miglit cx()cct to obtain somo edbct providcMl that ti>o velocity did not exceed 100 kilometres per second. Construction of the Apparatus. — The wheels wei-e made of brass one- sixteenth of an inch thick. The discs were flattened and turned true on a suitable hill), and were then soldered together at the ed^es so that the radial slots to be cut in the edges might exactly corres})ond. The slots were each a sixteenth of an inch wide, and half an inch deei>, and num- bered one hundred. The metal left between the slots was nearly four times the width of a slot. This proportion of slot to s])ace was necessary in order to secure a total ecliiwe, beciuso the ray.s necessarily formed a conical pencil. When the .slots had Ijen cut, the discs were separated, and fixed on a brass tube axis, at a distance of a nietre aj)art. with the . corresponding slots in each on a line parallel to the axis of rotation. This precaution was essential for the method which we ])roposed to adopt, because although the slots were cut on a very good riiilling machine, it is doubtful whether the accuracy of the divi.sion would have Ijeen sutli- cient to make each ]iair of slots give exactl}' similar etlects unless they had been simultaneously cut. The brass tube carrying the discs, wastitted with steel pivots tui'ning in suitable bearings in the end of a long wooden box, which was covered with tin plate and at the entls with thick sheet lead. The X-rays were admitted at one end of the box through a small tube titted with a lead cap. After passing through a pair of corres))onding slots in the two wheels, they were observed b}' means of a small tluoroscope. or by means of a small camera, each protected by a doub''> thickness of aluminum foil, at the other end of the box. The ad justraent and setting of the ap]iaratus in each case could be very easily and exactly performed by the aid of common light. In this manner wo tested the exact correspondence of the slots, which was found to be very satisfactory, and also the steadiness of the apparatus when driven at a high speed. With this a])paratus it was possible to use three ditferent but closely related methods, for the attempt to measure the velocity. These methods may be called (1) the method of Aberration, (2) the method of Total Eclipse, and (3) the method of Partial Eclipse. The methods all gave the same resiilt, but of the thne the third method appeared to be the mo.st satisfactory. (1) The Method of Aberration. — For the application of this method, the axis of observation was aligned by optical observation of the small red-hot focus point on the platinum plate, in such a manner that the focus point was just visible through a pair of corresponding slots when the latter were in the centre of the tield of view. The distance from 184 ROYAL SOCIETY OF CANADA tho focus point to the ticiiror whcid was 51) cm., and the (litiiii. of tlio focus point was about Ifiiniii., being as nearly aw could be judged tho Munie UH tho width of one of tho slots in the wheels. Uiulor these con- ditions, it was plain that tho apj)oarance presented on tho photographic plate, if the wheels were slowly rotated, should 1 e that of an umbra 1(1 mm. in width, fringed on either side by u penumbra of tho same extent. More exactly, if h is tho width of a slat, and c the diam. of tho focus point, the widtli of tlio umbra slK)uld be 'Ib—r. and tho total width of the band including ))enumbra 2/>-f '• Tliis, in fi'-^, proved to be tho case. The etlect of aberration sho\ild 1 ave been to shift the bands in the direction of rotation by a displacement ecjual to tlio distance turned through by tho wheels during tho time taken by the rays to traverse the interval between them. By means of a horizontal slot a little less than a quarter of an inch wide in a brsiss plate, it was |)o.ssible to expose one half of the jjlate while the wheels were tui'iiing very slowly, and tho other half at the highest speed. Hx[)osures were made for one minitto intervals alternately on the two halves in order to eliminate tho oilect of any possible change in the discharge, or in -tlie relative jiosilionsof the focus tube and box. In general, each half was thus exposed for five minutes. No displacement could in an}' case be detected, using a circum- ferential velocity of 2") metres per second. (2) Method of Total Eclip&e. — For tho application of this method, a brass tube was fitted along the axis of observation between the two wheels. Tlie ends of this tube were closed by discs having slots cut in them of the same width and size as those in tho edges of the wheels, '['he slots in the ends of the tube wore set very close to those on tho wheels, and accurately parallel to them. The end of tho tube nearest to the i)hotographic plate, was provided witii a screw adjustment, by which it could be shifted in a direction at right angles to the slots, while at the same time the parallelism of tho slots was maintained as accuratel}' as possible. If the position of the tube was adjusted so that any part of the slot in the end of the tube nearest the X-ray focus, was open at the moment when a slot in the wheel coincided with tho slot in tho tube at the other end, the image obtained on the photographic i)lato was un exact outline of tlie whole width of tho slot in the end of tho brass tube nearest to the plate. Wy tlie aid of ordinary light it was very easy to make the adjust- ment so that one slot just began to open at the moment when the other dosed! Uuder these conditions, the two slots wore never open together, and the light was just totality eclipsed. A movement of a thousandth of an inch in the screw adjustment, was sufficient to restore a very a])preci- able amount of light. It was therefore very necessary that the slots in the wheels should be cut to correspond as accurately as possible. For- tunately this had been foreseen, and the cutting of the slots was found to be sufficiently exact, when tested in this manner. tcox A CAixHNDAKl EXPEUIMENT8 ON THE X-KAYS '. 188 Tilt' totiil I'cIipsH having hooii udjustod in such ii rnnnruM* tliat tlu'slot at the caiiusra oiid wuh jiint on tho |)(iint of opeiiinjif at tho iiioinont wln'n the other dosod, five minute oxpowuros wci'i' tuUcn allcrnatt'ly as hcd'oro ul a low and high speed on the two halves of a plate (or the s|)aee of more than an hour. Both halves of the i)late developed |)erfectly eleur. Tho setting was so tine that if the velocity of the rays had In-en less than 200 kilometres per second, some light must certainly have been restored by tho rotation. (3) The Mel hod of Partial J^rlijisr. — The method of total eclipse, if the setting wer(» suftioiontly tine, ntlbrded jierhaps the most delicate to.«t of the velocity of the X-rays. At the same time, it was so far unsa- tisfactory that it gave only a i)erfectly clear ]>lato showing no record whatever of tlio time and trouble spent in producing it. If tho velocity had been measurably small, it could have been iletermiiiod by tliis method, either by observing the width of the baml of light I'eslored at a given speed of rotation, or by observing the sjieed required to rej)roduce the total oclipso at tho other side of the slot. To secure this latter result with our a])i)aratuH at a speed of 25 revolutions per second, the velocity of tho X-rays must have been as low as 1 kilometres per second, or not more than about 20 times the velocity of sound. That we had succeeded in reproducing the ecli])so, was a ])ossible, though not a liUely. inter])r'.'- tation of our failure to secure any result by the total eclip.se methou. Tho intensity of tho rays is of course excessively weakened by tho dis- tance, and n\ore particularly by the pas.sage through so many tine slots. Tho failure to atlect the jjlale might have lieen attributed to lack of intensity of the rays, or to want of ])ropcr alignment on the focus point. Wo thorefore used the most powerful radiation which wo could produce without molting the platinum ])lato, and we veritied the setting of the axis on the focus ])oint both before and aitei- the ex])Osuro. In rejx'ating tho experiment on two subsequent occasions, wo adopted the method of partial eclipse. The tube was set so that the near slot had already opened by about half a millimetre or one-third of its width at the moment when the far slot closed. The shadow of the slot ob'^ained in this way on tho plate, would bo conclusive evidence with regard to tho alignment and tho sufficiency of tho exposure. Tho velocity of the rays, if measui-able small, could also be measured by the widening of tlio shadow. The method of partial eclipse was tried in this manner on two occasions with exposures of upwards of half an hour. Tho photographic image obtained was a sharp narrow band half a millimetre wide, coi'res- ponding exactly with tho sotting of the slot. The two halves of tho band, corresponding to the exposures at tho high and low 8])eed respec- tively, coincided so exactly that no break could be detected at the point where they met. The fedgo of the band was so well defined, and the 186 ROYAL SOCIKTY OF CANADA l)iiii(i itsolf HO luiiTOW, that ti widening of a qiiiirlur of ii niilliiiiotro, corrospoiidiiijf to un X-ray velocity of 100 kiloiiietn's per hocoiuI, could not fail of hciuff readily detcctod. In fact, tho lower liir't of tho velocity HO far as may lut jiuli(t'(l tVoin tlu' evidence of these exporiiuonts, is in all pvobaliility not less than 200 kilometres per second. While theses experiments cannot be rcf^u'-ded as proving that tho X- niys do not consist of olot'trilied atoms, as some physicists Hnpi)osod at tho time when experiments wore undertaken, they tit least appear to render it more improliable than wiu: at Hrst supposed. Such a stream of atoms in air at atmospheric pressure, miifht l»u expe(^ted to sutler ditfusion or absorption like the kathode or Tifnard rays. The velocity found is so many times <>[reater tliaii ordinary mol 'c\dur velocities, as to appear impi'ol>able even for an elect ritied atom. It is in the hi<.rhest dcijreo improbable that such atoms could penetrate solitl b(j(lies with the facility shown by the X-rays. The inference is eitlier that the ]»ropagation of tho X-rays is a process of exchange, if ])ropagated by tho aid of material particles, or much mcn-e probably that it is .some kind of wave motion in tho ether, of a frequoncy too groat to sutler regular refraction or reflec- tion. It is inlm-esling to compare tho present result with the lower limit of 314"4 kilometres per second given by Ilelmholtz in 1871 for the velo- city of propagation of electrical oscillations. Tho application of more refiiuMl niDtlioils to the X-rays, may succood in .showing that this velocity is the .same as that of light. Phijaioloijlral Effoc.ts of the X-Raijs. — It was natural to try whether tho X-rays produced any effect upon the retina or tho skin or parts of tho body ox)tosed to their action. Positive results have boon claimed in many cases though not by any observers of much repute. As stated by Ilontgen, we could not detect that the retina was sensitive to tho smallest extent to tho most powerful X-radiation which we could produce. This shows that the |)igment of tho retina does not fluoresce appreciably under the influence of the X-rays, as it does under the influence of tho ultra violet rays of the spectrum. Tho X-rays have also been credited with ])ro(lucing blisters and peeling of tho skin, and falling out of the hair. AVe l-.ave not observed those effects in tho most prolonged expo- sures. It is evident, however, that such ettbcts might be produced by tho electric sparks from the tube, if it wore placed too close to the skin, as is sometimes done with the object of shortouing the exposure. The direct light from the tube also contains a proportion of ultra-violet rays which are known to produce blistering if sufficiently intense. It was natural to imagine that the X-rays might possess germicidal properties similar to those of ultra-violet light. That this is not the case, however, has been shown by the agreement of tho negative results of many competent observei-s. With the assistance of Dr. AVyatt Johnston, we submitted cultures of typical bacilli in jelly to the action of (oox A callksimk] rXF'KKIMENTS ON THE X-RAYS 187 tho mos* ntenao X-ru • • 3 6 • « • » * • • f 188 KOYAL SOCIETY OF CANADA Dbscrm'tion of Plates. The accompiinyiniz; illustnitlons rcferto tlio ciiho (if tlio ciivily in tho lun^ mentioned on l>ai^e 174. By way of'contnist, ii similar photograph of u healtiiy lung is given in IMato II. Hoth pholograplin are reduced about two-thirds from tlio original negatives. The cavity in Plate I is bounded aliove and below by the shadows of the ribs, and on the outer side by tiie shadow of the scapula. On the inner side its margin is less sharply detined. The cavity is whown by an extremely dense black jiatch in the original negative, and remains white after most of tlie other detail has vanished in the printing. The litferencos of density in the negative are, in fact, so great, that it is practically impossible to reproduce them by any process of printing. In jtrinting these negatives sutticiently to sliow the cavity, the fainter detail of the spinal column is wholly lost, and, yet, the cavity is far less clearly shown than in the original. In reducing the plates it was necessary, first, to print them on ordinary silver pajier, then to obtain a reduced negative by the wet process, which was printed on the xinc ])late. Since it is possible to obtain X-ray nega- tives of almost any degree of density, it is very likely that it will be found possible to print direct from the original negative in many cases, and thus to avoid the excessive loss of detail incidental to repeated copying. .• ♦ / ♦ • • * • • • • * • •••••• • • t • • • 190 KOYAL HCKIKTY OK ( ANAI>A PLATE I,-CAVITY IN LUNG. [cox .» rAU.KNDAu) SOM K KXI'KKIMKNTH ON THK X-UAYS Idl i'LATE ll.-HEAl/fHY LUNG.