One day in 1895, a physicist named Wilhelm Conrad Roentgen began fiddling with a cathode-ray tube in his laboratory at Wuerzburg University in Germany. The tube itself contained a glass bulb surrounded by positive and negative electrodes; when high voltage was applied, the tube produced a fluorescent glow. Intrigued, Roentgen covered the tube with heavy black paper and observed that crystals located near the tube emitted that same greenish fluorescent hue.
He knew he had discovered something major — a new type of ray that could pass through most substances while casting shadows of the solid objects it could not pass through. Most importantly, he found that while the ray could pass through human tissue, it could not make its way through bones and metal objects. This laid the groundwork for a huge component of modern medicine — what we know today as the fields of radiography and radiology. Not yet knowing exactly what he had stumbled upon, however, Roentgen named his mysterious discovery the “X-ray.”
The Variable X
“X” has long stood as a substitute for an unknown variable. This phenomenon most frequently appears in algebra, where the letter “x” often represents an unknown quantity. This traces back to algebra’s roots in the Middle East; the letter itself traces back to the Arabic word for “thing,” which is šay'. In the Al-Jabr, a mathematical manuscript written in Baghdad in 820 CE, author Muhammad ibn Musa al-Khwarizmi referred to variables as “things” or أشياء (ashya) — for example, “three things equal 12,” with the “thing” in question being the number four. Later, when the Al-Jabr was translated into Old Spanish, the word šay' became xei, which was eventually abbreviated to “x.”
The use of the letter “x” as a variable isn’t limited to mathematics, though. Other contemporary examples include Malcolm X, who chose the symbol to represent the forgotten names of his African ancestors, or the popular talent show The X Factor, which alludes to that mysterious characteristic one must have to achieve fame — you've either got “it,” or you don’t.
The X-Craze
Roentgen’s X-ray discovery immediately created a stir, both in the medical community and the popular culture at large, although no one really understood the technology yet. One newspaper headline read, "New Light Sees Through Flesh To Bones!" and much of the craze surrounding the new technology arose from a fear that the rays would allow people to see underneath one another's clothing. In New Jersey, an Assembly member introduced a bill prohibiting the use of X-rays in opera glasses, to ensure that patrons couldn’t see the naked bodies of the performers. Some companies even began marketing lead “X-ray-proof” underwear.
The letter “X” remains an enigmatic reference in marketing, such as using “Brand X” to refer to a generic product. Microsoft also used the letter for its Xbox 360 product to promote the idea of a generic video game console that could play a wide range of games.
The Mystery Remains
Scientists today understand X-rays a lot more, to the extent that entire fields of medicine revolve around the technology — radiography and radiology. Researchers eventually discovered that X-rays were merely another type of wave. Gamma rays and X-rays are both forms of electromagnetic radiation, widely used in medical treatments. The other types of radiation are called alpha, beta, and neutrons.
Roentgen himself was a mysterious man. He was awarded the first-ever Nobel Prize in physics in 1901 for his discovery, but upon his death, his will stipulated that all of his papers and notes be destroyed. Little did he know the mysterious ray he named “X” would eventually uncover some of the greatest mysteries in our universe.
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