Hand with Ring

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Hand with Ring

X Rays Discovered by Accident


By: Wilhelm Conrad Roentgen

Date: December 22, 1895

Source: Wellcome Trust Medical Library.

About the Photographer: Wilhelm Roentgen (1845–1923) was a German experimental physicist who was educated at Zurich Polytechnic and went on to teach at several universities in Germany. While he was professor of physics at Würzburg, he discovered x rays in 1895. In 1901, he was awarded the first Nobel Prize in physics for this discovery.


It is widely believed that this photograph shows the hand of Roentgen's wife, complete with ring. However, this is an image created by x rays rather than visible light. In 1895, Roentgen had discovered what he described as eine neuer art von strahlen (a new kind of ray) completely by accident. He was, at the time, working on the conduction of electricity in gases using a device called a Crookes tube. He noticed that something emitted from the tube created a strange glow on a card coated with a fluorescent chemical.

Quickly, he proceeded to investigate the properties of this new form of radiation, which he called x rays. He found that they traveled in straight lines and could pass through objects that were impervious to light. In fact, x rays penetrate the human body to a greater or lesser extent depending upon tissue density. They pass through skin, fat, blood, and muscle more easily than through bone. So, as the picture here shows, the bones cast a shadow. X-ray images can be captured on a fluorescent screen or upon film. Their ability to help physicians see inside the body was quickly realized by Roentgen and others. As early as March 1896, a doctor in Chicago described x-ray plates showing "bones of the hand and leg and a few coins and keys in a pocketbook."

Roentgen subsequently investigated other properties of x rays. He believed they were a source of electromagnetic radiation, like light and ultraviolet radiation but with a much shorter wavelength. They were produced in the Crookes tube when the electrons emitted from the tube's cathode struck the edge of the tube. Today, x rays are produced when a stream of electrons strikes a heavy metal target.



See primary source image.


Roentgen's discovery of x rays is a famous example of serendipity—lucky chance—in science. He was not looking for a new form of radiation but when he found it, he dedicated himself to understanding its nature, properties, and applications. Since their discovery, x rays have found increasing use in medicine—from diagnosing broken bones to screening for tuberculosis (TB) and breast cancer. Indeed, one of the earliest applications of x rays was to revolutionize the diagnosis of TB. Before antibiotics, TB was treated by rest in a sanatorium and it was widely thought that early diagnosis was essential if this treatment was to have a good outcome. Using x rays to look for a "shadow" on the lung proved far easier than the traditional method of TB diagnosis—listening for supposedly characteristic chest sounds.

Today, computed tomography (CT) scans are a more sophisticated version of the traditional x ray. To create a CT scan, a series of x-ray images taken from different angles are analyzed by a computer to produce a cross-sectional picture of the part of the body under examination. CT scans produce more detailed imaging, and they are increasingly used in planning more precise surgeries.

X rays are high-energy radiation and, as such, they can be damaging to healthy tissue with excessive exposure. After Roentgen's discovery, it was soon noted that prolonged exposure to x rays would burn the skin. Many patients and health workers suffered ill effects because the early x-ray machines were used without protection. The damaging effects of x rays, however, were used to advantage as well. Within a year of Roentgen's discovery, a doctor in Vienna had applied x rays to burn a mole off a patient's skin. Today, x rays are still used in one form of radiotherapy for cancer. A beam of x rays, narrowly focused, can destroy tumor tissues. The more precise the targeting of the x rays, the more healthy surrounding tissue is spared their damaging effects.

The British father and son team William (1862–1942) and Lawrence (1890–1971) Bragg used x rays to investigate the three-dimensional structure of molecules and developed a technique known as x-ray crystallography. The Braggs found that x rays are deflected by the electrons in a crystal, creating a pattern on film that is related to the structure of the crystal. X-ray crystallography was used to determine the structure of DNA in 1953, a discovery that lies at the heart of modern biology and genetics. Determining the structure of biological molecules by x-ray crystallography also is increasingly important in drug discovery.



Lock, Stephen, John M. Last, and George Dunea, eds. The Oxford Illustrated Companion to Medicine. Oxford: Oxford University Press, 2001.

Porter, Roy, ed. Cambridge Illustrated History of Medicine. Cambridge: Cambridge University Press, 1996.