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Filipp fon LenardPhysicist
Date of Birth: 07.06.1862
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Content:
- Early Life and Education
- Scientific Breakthroughs
- Phosphorescence and Cathode Rays
- Lenard's Experimental Findings
- Nobel Prize and Later Career
- Weitere wichtige Entdeckungen
- Later Life and Legacy
Early Life and Education
Philipp Eduard Anton von Lenard was born in Pressburg, Austria-Hungary (now Bratislava, Czechoslovakia) to wealthy wine merchant Philipp von Lenard and Antonia Baumann. After his mother's early death, Lenard was raised by his aunt, who later married his father. He received his early education at home until age nine, then attended the city grammar school and the Pressburg Gymnasium, where he excelled in mathematics and physics. Lenard supplemented his studies by reading university textbooks and conducting physical and chemical experiments.
Despite his strong affinity for science, Lenard's father insisted that he pursue the family's winemaking business. He enrolled Lenard at the technical universities of Vienna and Budapest to study chemistry, a subject considered essential for viticulture. Lenard reluctantly joined his father's firm in 1882.
Scientific Breakthroughs
A year later, Lenard used his savings to travel to Germany, where he attended lectures by renowned chemist Robert Wilhelm Bunsen (inventor of the Bunsen burner). This visit further solidified his resolve to become a scientist. In the winter of 1883, Lenard enrolled at the University of Heidelberg, where he studied physics.
Lenard spent four semesters at Heidelberg and two at the University of Berlin, where he studied under esteemed scientists Bunsen and physicist and physiologist Hermann von Helmholtz. In 1886, he earned his doctorate with summa cum laude honors for his dissertation on the vibrations of water droplets. For the next three years, he worked as an assistant to German physicist Georg Quincke in Heidelberg.
Phosphorescence and Cathode Rays
During his university years, Lenard collaborated with his high school physics teacher, Virgil Klatt, to investigate phosphorescence. They discovered that certain materials exhibited phosphorescence only when they contained traces of certain metals. Lenard continued to study phosphorescence throughout his career, spanning over four decades.
After leaving Heidelberg, Lenard briefly worked in London and Breslau (now Wrocław, Poland). In April 1891, he became an assistant to Heinrich Hertz at the University of Bonn. Hertz, famous for experimentally confirming electromagnetic radiation predicted by James Clerk Maxwell, had discovered the photoelectric effect (emission of electrically charged particles from a surface struck by radiation, in this case ultraviolet).
One phenomenon that particularly interested Hertz was cathode rays, which traveled from the negative electrode (cathode) to the opposite end of a well-evacuated glass discharge tube. They had been studied by many scientists, notably English physicist William Crookes. Lenard's fascination with cathode rays began in 1880 when he read Crookes' article "Radiant Matter, or the Fourth Physical State."
Lenard's Experimental Findings
Hertz and Lenard decided to investigate cathode rays in a more convenient setting, outside the discharge tube. Since Hertz had discovered that cathode rays could penetrate thin aluminum foil, Lenard constructed a glass discharge tube with a small aperture at the anode (positive electrode) covered with such foil (later known as Lenard windows). By placing a second discharge tube in the path of the cathode rays instead of ordinary air, Lenard was able to obtain a longer beam of rays, part of which was isolated from the source, allowing for easier experimentation.
By deflecting the beam with electric and magnetic fields, Lenard demonstrated that cathode rays consisted of negatively charged particles. He was able to measure the ratio of their charge to their mass. Initially, Lenard believed that cathode rays were an immaterial radiation. He also found that these particles penetrated air and other substances to varying depths, with absorption roughly proportional to the thickness and density of the absorbing material. Rays emitted from discharge tubes operating at higher voltages, corresponding to higher particle velocities and energy, had greater penetrating power. Lenard pursued cathode ray research for the next twelve years.
Nobel Prize and Later Career
After Hertz's death in 1894, Lenard briefly served as acting director of the Institute of Physics at the University of Bonn. He taught at the universities of Breslau, Aachen, and Heidelberg for a year or two each. He was then appointed professor and director of the physics laboratory at the University of Kiel in 1898.
Despite the recognition his work received, Lenard often felt disdain and envy towards the achievements of other scientists. He held great respect for Hertz but, as his assistant in Bonn, sometimes felt that he was not treated with sufficient deference.
When Wilhelm Röntgen discovered X-rays in 1895, Lenard was disappointed not to have made the discovery himself. He subsequently referred to them as "high-frequency radiation" but never used their widely accepted name "X-rays" or "X-radiation." Moreover, Lenard claimed that, by lending Röntgen his discharge tube, he had contributed significantly to the discovery. After J.J. Thomson's discovery and recognition of the electron in 1897, Lenard asserted that he had priority. While Thomson provided a modern description of the electron, Lenard, even in 1906, described the electron as "electricity without matter, an electric charge without charged bodies," referring to it as "electricity in its pure state."
Weitere wichtige Entdeckungen
One of Lenard's major scientific achievements was his 1902 experimental observation that a free electron (which he called a cathode ray) must exceed a certain minimum energy in order to ionize a gas (render a neutral gas electrically charged) by knocking out a bound electron from an atom. Lenard called the ejected atomic electrons secondary cathode rays. He made a remarkably accurate estimate of the ionization potential (energy required to eject the electron) for hydrogen.
In the same year, Lenard demonstrated that the photoelectric effect produced the same electrons found in cathode rays. He found that photoelectrons were not merely liberated from the metal's surface but ejected with a definite energy (velocity). The number of electrons emitted by the metal increased with increasing radiation intensity, but the velocity of the electrons never exceeded a certain limit. Albert Einstein (1905) explained these experimental results using Max Planck's quantum theory. According to Einstein, light was composed of tiny discrete packets of energy, later called photons. The energy of a photon was proportional to the frequency of light. In the photoelectric effect, each photon transferred its energy to an electron in the irradiated metal surface, potentially allowing the electron to "escape" from the metal. The greater the light intensity, the more photons and the more liberated electrons, but the fixed energy of the photon sets an upper limit on the speed of each electron.
Later Life and Legacy
In 1903, Lenard proposed that an atom was mostly empty space. He arrived at this conclusion by observing how electrons passed through Lenard windows and penetrated air and other substances. Lenard suggested that the positive and negative electrical charges within an atom (whose quantities must be equal to ensure its electrical neutrality) occurred in tightly bound pairs, which he called "dynamids." Lenard's concept was an interesting and significant step forward from previous views, but it was incorrect, as proven eight years later by Ernest Rutherford, who proposed an atomic model where negatively charged electrons orbited a very dense, positively charged nucleus at relatively large distances.
Although Lenard often came tantalizingly close to making discoveries that brought great recognition to others, the 1905 Nobel Prize in Physics was awarded to him "for his work on cathode rays." In presenting the award, Arne Lindsteadt of the Royal Swedish Academy of Sciences remarked, "It is clear that Lenard's work on cathode rays has not only enriched our knowledge of these phenomena, but has also laid in many respects the foundations of electron theory."
In 1907, Lenard succeeded Quincke as professor of experimental physics at the University of Heidelberg. In 1909, he also assumed the duties of director of the newly established Radiological Institute in Heidelberg. The most significant work conducted under his leadership at this institute involved spectral analysis of light emitted by excited atoms and molecules.
While Lenard's reputation in some scientific circles in Germany remained high, it began to decline. His 1910 lecture on the ether permeating space, an idea by then largely discredited, was characterized by Einstein as "infantile." Moreover, from the outbreak of the First World War, Lenard became an ardent nationalist and repeatedly attacked the English, accusing them of unjustly appropriating the achievements of German scientists. After Germany's defeat, he condemned the Weimar Republic for "tolerating Germany's disgrace" and encouraged students to rebel against the regime. Lenard was among the earliest supporters of Adolf Hitler and became an anti-Semite.
Lenard had a natural inclination for experimental research, which he called "pragmatic, truly German physics," and he harbored a distaste for physical theories laden with complex mathematics. Lenard referred to such theories as "dogmatic Jewish physics." He held particular animosity towards Einstein, fiercely attacking him (with "an unmistakable anti-Semitic undertone," according to Max Born) at a scientific congress in 1920. He even overrated Hertz's scientific legacy, dividing it into good experimental work and bad theory, which he attributed to the scientist's Jewish ancestry.
After the Nazis came to power in 1933, Lenard was appointed head of Aryan, or German, physics and became a personal advisor to Hitler. He presented the Führer with his own racially oriented version of physics. Lenard had married Katharina Schlenner in 1897. After leaving Heidelberg in 1945, he settled in the village of Meßhausen, where he died two years later.
Most scientists condemned Lenard's ideological biases, which clouded his judgment about physics in his later years. Karl Ramsauer, Lenard's student and colleague for over thirteen years, called him a "tra
