edited by
JOHN H. WOTlZ Southern iilinois University
Carbondale, Illinois 82901
X-Rays and After Ronald A. Brown The Polytechnic of North London Holloway, London N78DB England The way in which science advances has been an intriguing topic for many years. Breakthroughs often result from accidents, near accidents, serendipity, or what Harold Rugg ( 1 ) termed the precisely needed juxtaposition of events. For those who regard the scientific enterprise as an essentially orderly and methodical process, such chance occurrences sometimes seem difficult to accept. In Novemher 1942. H. R. Robinson was lecturing on the life and work of Krnesr Rutherford at the Physical Society. As an aside. Professor Hot~insonmentioned that Riintren had come u p o i X - r a y s largely by accident (2). Almost hmediately, Russ (3) took issue with this oninion. Suhseauentlv, there was a smail flurry of corresponden>e (4-6) concerningihe validity of this viewpoint, together with somediscussion on thegeneral role of accidents in scientific discovery. Professor Russ ended his note with the following remark. "Did Rontgen really discover X-rays, and if so, was it an accident? My usual answers until now have been Yes and No." These questions and answers are ones which I should like to re-examine in the present article. In addition, we shall consider the impact of Rontgen's findines in various areas. u Tracing the genesis of an event or concept in science is not alwavs straiehtforward. In the case of X-ravs, there is little doubt that many factors contributed to their jnitial exposure.' Perhaps an appropriate place to start is with "kathode" rays. Following on from the work of Hittorf, Crookes, Hertz, Thomson, Lenard, and others on what we would recognize now as cath#,derays, many inwst~ystorstook up studic.~ on this type enlanation. R). the lncf yrtirs of the nineteenth century cathode ravs were in widesnread use. not onlv for the nroduction of discharges in gas&, but also to exciteuluminescence in solid materials. Sometime during the summer of 18952 Wilhelrn Conrad Rontgen, Professor i f Experimental Physics and Director of the Phvsical Institute a t the Universitv of Wiirzburg, decided to start work on cathode rays, since it seemed likelv that there was still much to uncover in this exciting fir,ld. k t this stage of his carrer Runtgen hnd already ptthlished .48 paprrs in different areas of physics;' had prwed t u he a wrv citpahle, prrcise cxperimental~it,and was highly regarded 11yhis peers. His workingspuwcompristnl taosmall luhurntories set mart from tht, main Cn~veriitvhuildincs. and attached to his own living quarters. This arra&ementUsuited his rather retiring nature. The apparatus assembled consisted essentially of a Ruhmkorff induction coil equipped with a Duprez interruptor, which produced sparks of some 10-15 cm in length. Connected to this coil were the two electrodes of a Hittorf-Crwkes device (forerunner of the modern cathode rav tube). A Raps vacuum pump, screen coated with barium platinocvanide which was known to fluoresce under cathodoexcitation, and photographic plate to record effects of the cathode rays, completed the assemblage. Although this type of eauioment was auite . common and found in manv laboiatories or lecture rooms, it is likely that ~ i n t g e n ' sexp&imental capabilities produced some improvements over his contemporaries, for example in attaining better evacuation of the tubes (7.8). ~
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As was his custom when beginning a new enterprise, the first experiments were designed to reproduce the work of others who were emininent in this field. On the evening of Friday, Novemher 8. 1895. this . ohvsicist was working alone on a . project carried out originally by Lenard ( 9 ) .In this work on glow discharges in evacuated tubes, Lenard had shown that cathode rays pierced aluminum foil, and penetrated air to a depth of a few centimeters. Apparently, Rontgen wished to shield the fluorescent substances outside the tube from the effects of the glow discharges inside the Crookes-Hittorf apparatus. Consequently, the whole of the equipment was surrounded completely with a light tight c ~ v e r i n gand , ~ the room was darkened. While carrying out some preliminary tasks intended to test the effectiveness of the coverings, Rontgen noticed quite suddenly that the screen" coated with barium platinocyanide, which was lying on a bench approximately 1 i awav from the rest of the aooaratus. showed a soot of luminescence. Rontgen realized immediately that he gad found somethine strange. .. . for it was well known a t that time that cathode rays were atmorhed hy nu mure that1 a few c e t i t i m e l r ~ of air. This accidental uccurrrnce was the start da11 u i the activities associated with Rdntgenstrahlen., That night Rdntgen worked furiously, to an extent where he upset his wife ~ e r t h a by e failing to appear for dinner. For thenext seven weeks he was absorbed completely in his studies-working feverishly, eating and also sleeping in the laboratory. No one was told of the discovery. Even his two senior assistants had ' I n "Physical Foundations of Radiology" by 0 . Glasser ( 2 3 ) Chapter 1has a genealogy of events that led to the discovery of X-rays. This listing commences with the work of Gilhert in the 16th century on electricity and runs to Thomson's studies on gaseous discharges in 1893. l t m cath,dr r a w h~ The onwt uf Rmtgen'\ i t j i t i > ~ inte;rw~tim< hrrn irr nsenrly a\June Ir(!Jl.ornsl a t e ; ~ i O c t ~ . lii!(i. ~ c r I hare, htmn a flXQW ~ I L ~ \ C P1 0~beS the muzt generall? acceptro. whwh is summer 1895. :'At this stage of his career Professur Riintgen had worked in areas as diverse as specific heats of gases; calorimetry;thermometry; effect of electricity on the plane of polarization of light; had shown that magnetic effects are produced in dielectrics moved between the charged plates ofa condenser; had published papers on surface tension and aptical properties. After his X-ray investigations, he wrote a further seven articles on coefficient of thermal expansion,electrical conductivity of crystals, piezoelectricity. Reference ( 8 ) lists all of Riintgen's papers but does not give full bibliographic details. Rontgen was well regarded by his contemporaries,such as Hertz, Helmholtz. and Lorentz. Rihtgen, an avid reader of scientific publications, hed a great depth of knowledge. Notice that it was not unusual for him to complete one area of work, then progress to something almost completely unrelated. Perhaps such an attitude might benefit a modern researcher! ' A covering of black paper, black cardboard, or black paper surrounded by tinfoil is suggested in various sources. According to the first paper, black cardboard was used. One of the reasons fur excluding light was that R"ntgen had very poor color perception, since he was in fact color blind tu the color green. Wne account states that the item which caught the attention of Rlintgen was the letter "A" painted in harium pbtinoeyanide on a screen. " T h e marrinye 10 Anna Hcrthu I.oduy t w k plrw
