During this century, his discovery has saved thousands of lives, not just by the power of this "invisible light" to picture bones, bullets and other foreign bodies under the skin, but also by its ability to destroy cancerous tumours.
For his achievement, Rontgen received the Nobel Prize in 1901, the first to be awarded. Although medical applications have dominated public perception, what Rontgen called "a new kind of rays" have revealed the underlying structures of many materials and have been at the foundation of many more Nobel prize-winning scientific advances.
In 1953, James Watson and Francis Crick made perhaps the greatest discovery of post-war science: that DNA, the molecular messenger of genetic heredity, had the shape of a double helix. They deduced the structure by using X- ray studies of DNA fibres carried out at King's College in London. At the University of Cambridge, the analysis of many hundreds of X-ray photographs over a period of some 30 years led Max Perutz to uncover the three-dimensional arrangement of atoms within haemoglobin, the first protein to be so analysed.
Rontgen's discovery did not represent the birth of the modern atomic age - that surely came with Max Planck's quantum theory of radiation in 1900 - but it was the moment of conception. It opened the way to Henri Becquerel's discovery of radioactivity on 1 March 1896, with the promise that the nucleus of the atom itself was vulnerable to decay and disintegration. Rontgen's description of his discovery, according to Dietrich Harder of the Institute of Medical Physics at Gottingen, represented "the splintering of the ice heralding the spring that brought forth the flowers of the theory of relativity and of atomic physics". Malcolm Cooper, professor of physics at Warwick University, has a more personal angle: "He didn't do any of this until he was 50, so there is hope for us yet!"
The news travelled fast from Wurzburg. Within a month, the new rays were called Rontgenstrahlung. Rontgen was asked to demonstrate his experiments to the German emperor. The British physicists Lord Kelvin in Glasgow and Arthur Schuster in Manchester received copies of Rontgen's scientific paper direct. The news was reported publicly in Britain by the Daily Chronicle on 6 January 1896, but was passed over by the Times. The formal translation of the scientific paper was published in the journal Nature on 23 January 1896.
One of the first X-ray pictures ever taken was of Frau Rontgen's hand - her wedding ring is clearly visible circling the bones of her finger. Less than a year after the discovery, X-rays were being used not just as a medical diagnostic aid, but in the treatment of skin disorders, including cancer.
There was a darker side as well, though. Burns to the hands of X-ray workers were being reported within four months of the publication of Rontgen's scientific paper. In just five years, 170 cases of radiation injury were reported and by 1922, about 100 radiologists were known to have died of the results of overexposure.
Yet, although it might at first sight seem paradoxical given their potential to cause cancer, X-rays are fundamental to curing cancer in modern medical practice. According to Ann Barrett, professor of radiation oncology at the University of Glasgow, "of the patients who are cured of cancer, 50 per cent will have received radiotherapy either alone or as part of the treatment. Only 2 per cent of cancers are cured by drugs alone, despite the spectacular advances in treatment there have been." Where a cancer is still localised and has not spread, surgery to cut it out remains the most effective treatment, but radiotherapy, almost always X-rays, "is still one of the most important parts of any cancer treatment", Professor Barrett says.
According to her, "the biggest improvement has come with conformal techniques - we can now shape the beam to conform to the shape of the tumour by adjusting rods in the head of the machine". This can be allied to 3-D imaging techniques to display on a computer screen the exact shape of the tumour and the position of surrounding organs so that the clinician can determine exactly how to shape the beam in three dimensions. This delivers the maximum amount of radiation to the tumour, while minimising any radiation damage to surrounding tissues.
One of the biggest advances in radiation therapy for cancer has come from understanding the basic science of the proliferation of tumour cells, Professor Barrett continues. In June this year, a five-year study funded by the Medical Research Council reported that tumours grow very rapidly and concluded that treatment may have to be given more frequently than the current standard of once a day, Monday to Friday, for six weeks. The study concentrated treatment into 12 days where radiotherapy was administered three times a day, including weekends. The results were dramatic, with a 10 per cent improvement in the long-term survival of lung cancer patients, whereas the most that could be expected of new treatments would be a 3 or 4 per cent improvement.
The world's largest X-ray machine, the European Synchrotron Radiation Facility (ESRF), opened for business at Grenoble in France last year. It is difficult to imagine a machine more different from the bench-top apparatus that Rontgen had employed a century earlier. Covering a large site, the first phase of its construction cost Fr2.2bn (pounds 294m); the second phase will cost a further Fr400m, while its annual operating cost is Fr1bn. The ESRF resembles a particle accelerator - popularly known as an "atomsmasher" - not least because the technology has been spun off from the science of subnuclear physics. Subatomic particles - electrons - race round a circular vacuum tube 844m long. As they circle inside this storage ring, they give off intense beams of X-rays, known as synchrotron radiation.
Professor Cooper will be in Grenoble at the end of this week intending to use the X-rays to "look with high resolution at the fundamental structure of high-temperature superconductors". These are materials that lose all their resistance to conducting electricity when they are cooled to temperatures around that of liquid nitrogen. If researchers can understand the atomic structure of these materials they might be able to design compounds that are superconducting at still higher temperatures or that could carry more electric current before losing their superconductivity. Professor Cooper's main aim is "trying to understand the nature of magnetism especially in materials for new magnetic structures". Among the advantages of the ESRF, he said, are that "you can look at materials that are shortlived or make studies of chemical reactions as they proceed and because the beam has a time-structure you can do 'time-lapse' X-ray photography. You don't have these possibilities in the laboratory."
For Professor Jean-Patrick Connerade of Imperial College, London, "the attraction is that if you build a source of X-rays like the ESRF, you attract people from many areas of science that are unrelated by subject but related by the technique they use. They come together round the same machine and this produces a kind of cross-talk among the scientists and new growth in science comes from that kind of exchange."
One hundred years on, Wilhelm Rontgen's discovery is proving as fruitful as ever.