by John Carey
The most striking feature of this phenomenon is the fact that an active agent here passes through a black cardboard envelope, which is opaque to the visible and the ultra-violet rays of the sun or of the electric arc; an agent, too, which has the power of producing active fluorescence. Hence we may first investigate the question whether other bodies also possess this property.
We soon discover that all bodies are transparent to this agent, though in very different degrees. I proceed to give a few examples: Paper is very transparent; behind a bound book of about one thousand pages I saw the fluorescent screen light up brightly, the printers’ ink offering scarcely a notable hindrance. In the same way the fluorescence appeared behind a double pack of cards; a single card held between the apparatus and the screen being almost unnoticeable to the eye. A single sheet of tin-foil is also scarcely perceptible; it is only after several layers have been placed over one another that their shadow is distinctly seen on the screen. Thick blocks of wood are also transparent, pine boards two or three centimetres thick absorbing only slightly. A plate of aluminium about fifteen millimetres thick, though it enfeebled the action seriously, did not cause the fluorescence to disappear entirely. Sheets of hard rubber several centimetres thick still permit the rays to pass through them. (For brevity’s sake I shall use the expression ‘rays’; and to distinguish them from others of this name I shall call them ‘X-rays’.) Glass plates of equal thickness behave quite differently, according as they contain lead (flint-glass) or not; the former are much less transparent than the latter. If the hand be held between the discharge-tube and the screen, the darker shadow of the bones is seen within the slightly dark shadow-image of the hand itself … Lead of a thickness of 1.5 millimetres is practically opaque …
I have observed, and in part photographed, many shadow-pictures of this kind, the production of which has a particular charm. I possess, for instance, photographs of the shadow of the profile of a door which separates the rooms in which, on one side, the discharge-apparatus was placed, on the other the photographic plate; the shadow of the bones of the hand; the shadow of a covered wire wrapped on a wooden spool; of a set of weights enclosed in a box; of a galvanometer in which the magnetic needle is entirely enclosed by metal; of a piece of metal whose lack of homogeneity becomes noticeable by means of the X-rays, etc. I have obtained a most beautiful photographic shadow-picture of the double barrels of a hunting-rifle with cartridges in place, in which all the details of the cartridges, the internal faults of the damask barrels, etc., could be seen most distinctly and sharply.
Roentgen’s discovery was publicized in the world’s press, and caused great excitement. A reporter, H. J. W. Dam, interviewed Roentgen in his laboratory and described what ensued for readers of McClure’s Magazine (New York and London) in April 1896.
In addition to his own language he speaks French well and English scientifically, which is different from speaking it popularly. These three tongues being more or less within the equipment of his visitor, the conversation proceeded on an international or polyglot basis, so to speak, varying at necessity’s demand.
‘Now then,’ he said smiling and with some impatience, when some personal questions at which he chafed were over, ‘you have come to see the invisible rays.’
‘Is the invisible visible?’
‘Not to the eye, but its results are. Come in here.’
He led the way to a square room and indicated the induction coil with which his researches were made, an ordinary Ruhmkorff coil with a spark of from 4 to 6 in., charged by a current of twenty amperes. Two wires led from the coil through an open door into a smaller room on the right. In this room was a small table carrying a Crookes’ tube connected with the coil. The most striking object in the room, however, was a huge and mysterious tin [actually zinc and lead] box about 7 ft. high and 4 ft. square. It stood on end like a huge packing case, its side being perhaps 5 in. from the Crookes’ tube.
The professor explained the mystery of the tin box, to the effect that it was a device of his own for obtaining a portable dark room. When he began his investigations he used the whole room as was shown by the heavy blinds and curtains so arranged as to exclude the entrance of all interfering light from the windows. In the side of the tin box at the point immediately against the tube was a circular sheet of aluminium 1 mm. in thickness, and perhaps 18 in. diameter, soldered to the surrounding tin. To study his rays the professor had only to turn on the current, enter the box, close the door, and in perfect darkness inspect only such light or light effects as he had a right to consider his own, hiding his light, in fact, not under the Biblical bushel but in a more commodious box.
‘Step inside,’ said he, opening the door which was on the side of the box farthest from the tube. I immediately did so, not altogether certain whether my skeleton was to be photographed for general inspection or my secret thoughts held up to light on a glass plate. ‘You will find a sheet of barium paper on the shelf,’ he added, and then went away to the coil. The door was closed and the interior of the box became black darkness. The first thing I found was a wooden stool on which I resolved to sit. Then I found the shelf on the side next the tube, and then the sheet of paper prepared with barium platinocyanide. I was thus being shown the first phenomenon which attracted the discoverer’s attention and led to the discovery, namely, the passage of rays, themselves wholly invisible, whose presence was only indicated by the effect they produced on a piece of sensitized photographic paper.
A moment later, the black darkness was penetrated by the rapid snapping sound of the high-pressure current in action, and I knew that the tube outside was glowing. I held the sheet vertically on the shelf, perhaps 4 in. from the plate. There was no change, however, and nothing was visible.
‘Do you see anything?’
‘No.’
‘The tension is not high enough,’ and he proceeded to increase the pressure by operating an apparatus of mercury in long vertical tubes acted upon automatically by a weight lever which stood near the coil. In a few moments the sound of the discharge again began, and then I made my first acquaintance with the roentgen rays.
The moment the current passed, the paper began to glow. A yellowish-green light spread all over its surface in clouds, waves, and flashes. The yellow-green luminescence, all the stranger and stronger in the darkness, trembled, wavered, and floated over the paper, in rhythm with the snapping of the discharge. Through the metal plate, the paper, myself, and the tin box, the visible rays were flying, with an effect strange, interesting, and uncanny. The metal plate seemed to offer no appreciable resistance to the flying force, and the light was as rich and full as if nothing lay between the paper and the tube.
‘Put the book up,’ said the professor.
I felt upon the shelf, in the darkness, a heavy book, 2 in. in thickness, and placed this against the plate. It made no difference. The rays flew through the metal and the book as if neither had been there, and the waves of light, rolling cloud-like over the paper, showed no change in brightness. It was a clear, material illustration of the ease with which paper and wood are penetrated. And then I laid the book and paper down, and put my eyes against the rays. All was blackness, and I neither saw nor felt anything. The discharge was in full force, and the rays were flying through my head, and, for all I knew, through the side of the box behind me. But they were invisible and impalpable. They gave no sensation whatever. Whatever the mysterious rays may be, they are not to be seen and are to be judged only by their works.
I was loath to leave this historical tin box, but the time pressed. I thanked the professor, who was happy in the reality of his discovery, and the music of his sparks. Then I said, ‘Where did you first photograph living bones?’
‘Here,’ he said, leading the way into the room where the coil stood. He pointed to a table on which was another – the latter a small, short-legged wooden one, with more the shape and size of a wooden seat. It was 2 ft. square and painted coal black.
‘How did you take
the first hand photograph?’
The professor went over to a shelf by the window, where lay a number of prepared glass plates, closely wrapped in black paper. He put a Crookes’ tube underneath the table, a few inches from the under side of its top. Then he laid his hand flat on the top of the table, and placed the glass plate loosely on his hand.
‘You ought to have your portrait painted in that attitude,’ I suggested.
‘No, that is nonsense,’ he said, smiling.
‘Or be photographed.’ This suggestion was made with a deeply hidden purpose.
The rays from the Röntgen eyes instantly penetrated the deeply hidden purpose. ‘Oh, no,’ said he, ‘I can’t let you make pictures of me. I am too busy.’ Clearly the professor was entirely too modest to gratify the wishes of the curious world.
The reception of the discovery by the public was not entirely favourable. Photographing the skeleton of a living person was felt to be eerie. A Professor Czermak of Graz was so appalled to see an X-ray photograph of his skull that he could not sleep. ‘He has not closed an eye since he saw his own death’s head,’ reported the Grazer Tageblatt. The possibility of seeing other people’s internal organs was widely considered a threat to privacy. But enthusiasm outweighed disapproval, and many potential uses of the new technique were suggested. In Paris a Dr Baraduc claimed that he could photograph the human soul with X-rays, and presented 400 such plates at an exhibition in Munich. During 1896 the use of X-rays in medical diagnosis was rapidly explored worldwide, especially in the USA. Photographs of a human foetus, of a tubercular patient’s lungs, and of the stomach, heart and other organs were published, and a Harvard professor, W. B. Cannon, watched pearl buttons pass down the oesophagus of a dog. The harmful effects of exposure to X-rays were soon noticed. Many cases of severe skin burns and loss of hair were reported, but no one appreciated the real danger. Noting their depilatory effect one enterprising Frenchman, M. Gaudoin of Dijon, offered to use X-rays to remove unwanted hair from women’s faces, and had many clients.
Dramatic use is made of early responses to X-rays in Thomas Mann’s novel The Magic Mountain (1924), which is set in a Swiss sanatorium in the years before the First World War. A student, Hans Castorp, has come to the sanatorium to visit his cousin Joachim, a patient there. The resident physician, Hofrat Behrens, takes him to the room containing the X-ray apparatus, where Joachim is to be examined.
They heard a switch go on. A motor started up, and sang furiously higher and higher, until another switch controlled and steadied it. The floor shook with an even vibration. The little red light, at right angles to the ceiling, looked threateningly across at them. Somewhere lightning flashed. And with a milky gleam a window of light emerged from the darkness: it was the square hanging screen, before which Hofrat Behrens bestrode his stool, his legs sprawled apart with his fists supported on them, his blunt nose close to the pane, which gave him a view of a man’s interior organism.
‘Do you see it, young man?’ he asked. Hans Castorp leaned over his shoulder, but then raised his head again to look toward the spot where Joachim’s eyes were presumably gazing in the darkness, with their gentle, sad expression. ‘May I?’ he asked.
‘Of course,’ Joachim replied magnanimously, out of the dark. And to the pulsation of the floor and the snapping and crackling of the forces at play, Hans Castorp peered through the lighted window, peered into Joachim’s empty skeleton. The breastbone and spine fell together in a single dark column. The frontal structure of the ribs was cut across by the paler structure of the back. Above, the collar bones branched off on both sides, and the framework of the shoulder, with the joint and the beginning of Joachim’s arm, showed sharp and bare through the soft envelope of flesh. The thoracic cavity was light, but blood vessels were to be seen, some dark spots, a blackish shadow.
‘Clear picture,’ said the Hofrat … ‘Breathe deep,’ he commanded. ‘Deeper! Deep, I tell you!’ And Joachim’s diaphragm rose quivering, as high as it could; the upper parts of the lungs could be seen to clear up, but the Hofrat was not satisfied. ‘Not good enough,’ he said. ‘Can you see the hilus glands? Can you see the adhesions? Look at the cavities here, that is where the toxins come from that fuddle him.’ But Hans Castorp’s attention was taken up by something like a bag, a strange, animal shape, darkly visible behind the middle column, or more on the right side of it – the spectator’s right. It expanded and contracted regularly, a little after the fashion of a swimming jelly-fish.
‘Look at his heart,’ and the Hofrat lifted his huge hand again from his thigh and pointed with his forefinger at the pulsating shadow. Good God, it was the heart, it was Joachim’s honour-loving heart, that Hans Castorp saw!
Sources: Charles Nootnangle, ‘How Roentgen Discovered the X-Ray’, The Electrical Engineer, New York, 22, 125, 5 August 1896; H. J. W. Dam, McClure’s Magazine, New York and London, April 1896. Both quoted in Otto Glasser, William Conrad Roentgen and the Early History of the Roentgen Rays, London, John Ball, Sons and Danielsson Ltd, 1933. George F. Barker, tr. and ed., Roentgen Rays, Memoirs by Roentgen, Stokes and J. J. Thomson, Harper and Bros, New York and London, 1899. Thomas Mann, The Magic Mountain, tr. H. T. Lowe-Porter, London, Penguin Books in association with Secker and Warburg, 1960.
No Sun in Paris
Henri Becquerel (1852–1908), Professor of Physics at the Ecole Polytechnique in Paris, read about X-rays soon after their discovery. He thought that similar penetrating rays might be emitted by phosphorescent substances when exposed to sunlight. So he took some phosphorescent crystals of a uranium compound, in the form of a thin crust, and placed them on a photographic plate which he had previously wrapped in thick black paper to keep the light out. Then he exposed the whole thing to the sun for a few hours. When he developed the photographic plate he found a silhouette of the crystals in black on the negative – which seemed to confirm his idea that sunlight made the crystals emit radiation.
His discovery that they emitted radiation even in the dark was a matter of chance. The sun did not shine in Paris for several days, but, as he had set up his apparatus, he decided to develop the plate nevertheless – as he explains in his paper ‘On the Radiation Emitted by Phosphorescence’ (1896).
I particularly insist on the following fact, which appears to me exceedingly important and not in accord with the phenomena which one might expect to observe: the same encrusted crystals placed with respect to the photographic plates in the same conditions and acting through the same screens, but kept in the dark, still produce the same photographic effects. I may relate how I was led to make this observation: among the preceding experiments some had been made ready on Wednesday the 26th and Thursday the 27th of February and as on those days the sun only showed itself intermittently I kept my arrangements all prepared and put back the holders in the dark in the drawer of the case, and left in place the crusts of uranium salt. Since the sun did not show itself again for several days I developed the photographic plates on the 1st of March, expecting to find the images very feeble. The silhouettes appeared on the contrary with great intensity. I at once thought that the action might be able to go on in the dark, and I arranged the following experiment.
At the bottom of a box of opaque cardboard, I placed a photographic plate, and then on the sensitive face I laid a crust of uranium salt which was convex, so that it only touched the emulsion at a few points; then alongside of it I placed on the same plate another crust of the same salt, separated from the emulsion by a thin plate of glass; this operation was carried out in the dark room, the box was shut, was then enclosed in another cardboard box, and put away in a drawer.
I did the same thing with a holder closed by an aluminium plate, in which I put a photographic plate and then laid on it a crust of uranium salt. The whole was enclosed in an opaque box and put in a drawer. After five hours I developed the plates, and the silhouettes of the encrusted crystals showed black, as in the former experiment, and as if they had been rendered phosphorescent by light. In the case of
the crust which was placed directly on the emulsion, there was a slightly different action at the points of contact from that under the parts of the crust which were about a millimeter away from the emulsion; the difference may be attributed to the different distances of the sources of the active radiation. The action of the crust placed on the glass plate was very slightly enfeebled, but the form of the crust was very well reproduced. Finally, in passing through the plate of aluminium, the action was considerably enfeebled but nevertheless was very clear.
It is important to notice that this phenomenon seems not to be attributable to luminous radiation emitted by phosphorescence … The radiations of uranium salts are emitted not only when the substances are exposed to light but when they are kept in the dark, and for more than two months the same pieces of different salts, kept protected from all known exciting radiations, continued to emit, almost without perceptible enfeeblement, the new radiations. From the 3rd of March to the 3rd of May these substances were enclosed in a box of opaque cardboard. Since the 3rd of May they have been in a double box of lead, which has never left the dark room. A very simple arrangement makes it possible to slip a photographic plate under a black paper stretched parallel to the bottom of the box, on which rest the substances which are being tested, without exposing them to any radiation which does not pass through the lead.
In these conditions the substances studied continued to emit active radiation.
All the salts of uranium that I have studied, whether they become phosphorescent or not in the light, whether crystallized, cast or in solution, have given me similar results. I have thus been led to think that the effect is a consequence of the presence of the element uranium in these salts, and that the metal would give more intense effects than its compounds. An experiment made several weeks ago with the powdered uranium of commerce, which has been for a long time in my laboratory, confirmed this expectation; the photographic effect is notably greater than the impression produced by one of the uranium salts.