Wilhelm Wien is best known for his studies of radiation. Of the two laws he developed dealing with this topic, one was later confirmed, and is now known as Wien's displacement law. The second law was later shown to be inadequate and was replaced by Max Planck's brilliant theoretical analysis of the quantum nature of energy emission. Although Wien never made discoveries later in life of the quality of those from his early career, he eventually became a highly respected leader of German science in the early part of the twentieth century.
Wilhelm Carl Werner Otto Fritz Franz Wien was born on January 13, 1864, on his family's farm at Gaffken, near Fischhausen, in East Prussia. He was the only child of Carl Wien and the former Caroline Gertz, both descended from land-owning Prussian aristocracy. When Wien was two years old, the family moved to a smaller farm at Drachenstein, in the district of Rastenburg. As a young child, Wien received private tutoring and learned to speak French before he could write his native German. He was quite introverted, however, and spent a great deal of time by himself riding and swimming. Wien's mother was a particularly strong influence in her son's life. She was responsible for operating the Drachenstein farm after her husband had become ill, and according to Wien's entry in the Dictionary of Scientific Biography, "her excellent knowledge of history and literature stimulated [Wien's] interest in those subjects." Wien was sent to the local Gymnasium at Rastenburg in 1875, but he showed little interest in his classes and was brought home five years later without graduating. For a period of time, he stayed at home learning agriculture and studying with another private tutor. He then returned to formal classes at the Königsberg Altstädtisches Gymnasium, graduating in 1882.
Undecided about Becoming a Farmer
At his mother's urging, Wien then enrolled at the University of Göttingen to study mathematics and natural science. After only one semester, he became bored and left the university, setting off for an extended vacation through the Rhineland and Thüringen. He returned home once again, convinced that as the only child in the family he should take over the farm from his parents. That commitment lasted only a few months, however, and he headed back to school again in the fall of 1883, this time to the University of Berlin.
His academic experience this time was very different. He came under the tutelage of the great German physicist, mathematician, and physiologist Hermann von Helmholtz and, according to his own reports, "really came into contact with physics for the first time." He now applied himself vigorously to his studies and in the spring of 1886 received his doctorate. His dissertation dealt with the behavior of light diffracted by the sharp edge of a piece of metal.
After receiving his doctorate, Wien returned yet another time to the Drachenstein farm. The occasion for this trip was a disastrous fire that had destroyed some of the farm buildings. For four years Wien remained in a mood of indecision, feeling that he should continue to operate the farm, but still maintaining an interest in physics and continuing to do research on his own.
Joins Helmholtz at Charlottenberg
In 1890 a decision was made for Wien. An extended period of drought forced the Wien family to sell the farm, and Wien decided to take a job as Helmholtz's assistant at the newly established Physikalisch-Technische Reichsanstalt in Charlottenberg, outside Berlin. His parents also moved to Berlin, where his father died less than a year later. In 1892 Wien was promoted to lecturer at Berlin and then, four years later, he was offered a position as professor of physics at the Technical University in Aachen. He remained at Aachen for three years before moving on to the University of Giessen in 1899 and then to the University of Würzburg in 1900.
Wien's most productive period was the decade of the 1890s, when his main area of interest was the nature of blackbody radiation . The term blackbody refers to a theoretical substance that absorbs all of the radiation that falls on it; the fact that it reflects none of the radiation makes it black. In the 1860s, Gustav Kirchhoff had thoroughly studied the thermal properties of blackbodies. He pointed out that they are a perfect tool for studying radiation since when heated they emit radiation of all wavelengths. This fact makes it possible to study in great detail the nature of radiation emitted at different temperatures.
In about 1893 Wien began a theoretical analysis of the characteristics of blackbody radiation beginning with the fundamental laws of thermodynamics. He eventually developed two important conclusions. The first of these, now known as Wien's displacement law, says that the wavelength of radiation emitted by a blackbody is inversely proportional to the temperature of the body. That is, at low temperatures a blackbody will radiate energy with a long wavelength (red light). As the temperature rises, the most abundant wavelength radiated becomes smaller, and the color of the emitted light changes to orange, yellow, and then white.
Wien next attempted to find a mathematical formula that would fit the empirical graphical representation of the relationship between the amount of energy radiated at each wavelength for various temperatures. He obtained a complex equation that works fairly well at short wavelengths, but not very well at long wavelengths. He published this result in June 1896. In the meantime John William Strutt (Lord Rayleigh) in England had derived a formula that worked well at long wavelengths, but not at short wavelengths. It was not until Max Planck introduced the concept of a quantum of energy in 1900 that the problem of blackbody radiation was finally solved.
By 1897 Wien had moved on to a new field of interest, cathode rays. Although he completed some excellent studies in this field, he did not produce any major breakthroughs. His two most notable accomplishments were probably his confirmation of the nature of cathode rays as rapidly moving negatively charged particles (1897-98) and of canal rays as rapidly moving positively charged particles (1905). He also carried out some of the earliest studies on the diffraction of x rays by crystals, anticipating the discoveries of Max von Laue in this area by at least five years.
Wien's tenure at Würzburg lasted for two decades, during which time he was awarded the 1911 Nobel Prize in physics for his work on radiation. He also traveled extensively, including trips to Norway, Spain, Italy, and England (in 1904), to Greece (in 1912), to the United States (where he visited Columbia, Yale, and Harvard in 1913), and to the Baltic states (in 1918). Wien's last academic position was at the University of Munich, where he became professor of physics in 1920. There he supervised construction of a new physics institute and served as rector from 1925 to 1926. He died in Munich on August 30, 1928.
Wien was married to Luise Mehler in 1898. They had two sons, Waltraut and Karl, and two daughters, Gerda and Hildegard. In addition to the Nobel Prize, Wien was honored with membership in the scientific societies of Berlin, Göttingen, Vienna, and Stockholm. He was also a member of the U.S. National Academy of Sciences. From 1906 until his death, he was joint editor with Planck of the prestigious Annalen der Physik and later, with F. Harms, of the Handbuch der Experimental Physik.
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