When the Dutch physicist and physical chemist Petrus Debye first arrived from Europe at Cornell University, Ithaca, New York, in 1939-1940 to deliver the Baker lectures in Chemistry, he was 55 years old, already a Nobel Laureate, and acknowledged as one of the greatest scientists of the twentieth century. He had been awarded the Nobel Prize in Chemistry for his contributions to the study of molecular structure through his investigations on dipole moments and on the diffraction of X-rays and electrons in gases.
After coming to the US, he accepted the position of Professor of Chemistry and Principal of the Chemistry Department of Cornell University in 1940 and took American citizenship in 1946. On retiring from this post in 1952, he was appointed as Emeritus Professor of Chemistry at Cornell.
Peter Debye, as he now came to be called, had achieved such a towering stature as a physical chemist internationally, that the American Chemical Society decided to name its annual award for an outstanding physical chemist as the ‘Peter Debye Award in Physical Chemistry’. In a tribute to him after he died, F. A. Long, the Vice-President and Professor of Chemistry at Cornell University said Peter Debye’s influence on the Cornell Chemistry Department and on Chemistry in the US was profound. It wouldn’t be too far-fetched to accept that his influence on chemistry in the world to has been immense.
Early education and distinguished academic career in Europe
Petrus (Peter) Josephus Wilhelmus Debye was born at Maastricht in the Netherlands on March 24, 1884. He completed his early education at the elementary and secondary schools in his hometown, and in 1901, joined the Aachen University of Technology, focusing on the study of mathematics and classical physics. In 1905, he completed his degree in electrical engineering, and two years later, published his first paper – a significant mathematical solution to a problem involving eddy currents. While at Aachen, he studied under the celebrated theoretical physicist Arnold Sommerfeld, who later openly referred to Peter Debye as his most important discovery.
In 1906, when Sommerfeld received an appointment at Munich, he took Debye along with him as his assistant in theoretical physics. In 1908, Debye got his Ph.D. in Physics with a dissertation on radiation pressure and thereafter qualified as a University lecturer in 1910. That same year, he derived the Planck radiation formula coming up with a method that even Max Planck agreed was simpler than his own.
In 1911, Debye took up the professorship at the University of Zurich, Switzerland that Albert Einstein vacated on joining the German Charles-Ferdinand University in Prague. After that, he changed universities every few years. He returned to the Netherlands as Professor of Theoretical Physics at Utrecht University in 1912, then moved to Göttingen, Germany in 1913 to lecture in experimental physics, thereafter to the Swiss Federal Institute of Technology (ETH), Zurich in 1920 as the Principal of the Institute and Professor of Physics, and then to the University of Leipzig, Germany in 1927 where he held a similar position. In 1934, he succeeded Einstein as the Director of the Kaiser Wilhelm Institute for Physics (now called the Max Planck Institute) in Berlin and was also Professor of Physics at the University of Berlin. From 1937 to 1939 he served as the President of the German Physical Society (DPG). The positions he held from 1934 to 1939 were during the years that Adolf Hitler ruled Nazi Germany.
Interestingly, despite his recurrent appointments as a theoretical physicist, Debye had also spent several years lecturing on experimental physics at Göttingen. It is believed that his close association with the experimental physicist Max Vien while studying at Aachen University helped him excel in experimental physics as well in later years. His last appointment was in the US at Cornell University where he continued engaging in research work till he died.
Remarkable scientist, brilliant teacher
The earliest of Debye’s several major scientific contributions was in 1912 when he developed equations to calculate the size of the molecular dipole moments and also determined information regarding the structure of molecules. The measurement of dipole moments plays a significant role in understanding the nature of the chemical bonds between the atoms in a molecule, distinguishing between polar and non-polar molecules, and determining the shapes of molecules. Debye’s work on the measurement of molecular dipole moments was so crucial that the units for these measurements are named Debye Units after him.
In 1912, the same year in which he studied the concept of dipole moments, Debye developed the Debye model for vibrations of atoms in solids extending Albert Einstein’s theory of specific heat to lower temperatures by including contributions from low-frequency phonons. In 1913, he extended Niels Bohr’s theory of atomic structure by introducing elliptical orbits. In plasma physics and colloid chemistry, the Debye length is defined as the distance over which mobile charge carriers such as electrons screen out electric fields. In 1923, together with his assistant Erich Hückel, he developed the Debye-Hückel theory of electrolytic solutions, an improvement over Svante Arrhenius’ theory of electrical conductivity in electrolyte solutions. In 1923, Peter Debye also developed a theory to explain the Compton Effect, named after American physicist Arthur Compton, discovering independently that collision with electrons causes the wavelength of X-rays to increase. All of these contributions bearing Debye’s name are significant extensions of the models proposed earlier by major scientists.
As a teacher, Debye’s devotion to his students and science was unmistakable. He was always courteous and friendly and always happy to discuss an interesting new idea with his students or visitors. He could as easily explain complex scientific ideas to school children as to his colleagues. F. A. Long, who was a freshly appointed assistant professor when Peter Debye first came to Cornell University had also written this in his tribute: ‘Those (Debye’s) lectures were lively, vigorous, and filled with that sense of intellectual excitement which I came to realise was a Debye hallmark.’ He said Debye’s lectures were greeted with much enthusiasm and that the Cornell faculty were overjoyed when he accepted the offer to stay on as Professor and Chairman of the Chemistry Department.
It is believed that the pressure from Hitler’s government to give up his Dutch nationality had made Debye decide to try to move to the US. A lot of his work at Cornell involved the use of light-scattering techniques, following on his X-ray scattering work done years earlier, for determining the size and weight of polymer molecules. When World War II broke out synthetic rubbers had been invented but it was essential to know their molecular weight. This was made possible by Debye’s research during the war on small angle light scattering. This research was later extended to include the study of proteins and macromolecules.
A book in Dutch by the Dutch writer-scientist Sybe Rispens published in 2006 insinuated that Peter Debye was a Nazi sympathiser who had removed several Jewish employees from the Kaiser Wilhelm Society during his directorship and as President of DPG and even signed off his letters with ‘Heil Hitler’. However, several in-depth investigations carried out subsequently in the Netherlands and the US revealed that Debye was apolitical. The earliest of these carried out by the Cornell University’s Department of Chemistry and Chemical Biology issued a report in May 2006 that states:
Based on the information to-date, we have not found evidence supporting the accusations that Debye was a Nazi sympathizer or collaborator or that he held anti-Semitic views. It is important that this is stated clearly since these are the most serious allegations.
Even decades before Rispens, several writers had clearly mentioned Debye’s staunch resistance to Nazi activities. Many scientists and scholars have pointed out that the DPG had succeeded in retaining their threatened Jewish staff as long as possible despite increasing pressure from the Nazis, and that as a civil servant, even Max von Laue, a leading opponent of the Nazis was obliged to sign letters with ‘Heil Hitler’. Besides, the help Debye and his colleagues extended at great risk to themselves and their families to their Jewish colleague Lise Meitner to cross the Dutch-German border and go to Sweden to escape Nazi persecution is well documented.
Others point out that when Debye received the Max Planck medal of the DPG in 1950, nobody, not even Einstein, Max von Laue, and other Jewish scientists who knew Debye closely, objected.
Awards and recognition galore
The honours bestowed on this outstanding scientist are too many to list here, running into scores, some of the prominent ones being the Nobel Prize in 1936, the Rumford Medal of the Royal Society, London in 1930, the Lorentz Medal of the Royal Netherlands Academy in 1935, London, the Max Planck Medal in 1950 by the West Germany Physical Society, and the Priestley Medal of the American Chemical Society in 1963.
Debye was a Visiting Lecturer at universities across the US and Europe and associated with numerous scientific academies across the world including the Indian Academy, Bengaluru, and the National Institute of Science in India.
We owe a number of the concepts in chemistry that we often take for granted today to Debye who proved these after meticulous experimental measurements. His passion for scientific work never flagged until the end. He died of a heart attack on 2 November 1966 at the age of 82 and is buried in the Pleasant Grove Cemetery at Ithaca, New York.
- Nobelprize.org: Peter Debye – Biographical – Nobel Media AB 2014 – https://www.nobelprize.org/nobel_prizes/chemistry/laureates/1936/debye-bio.html
- Elangannan Arunan: Peter Debye – Resonance, December 2010, Indian Academy of Sciences.
- FamousScientists.org: Peter Debye – https://www.famousscientists.org/peter-debye/
- F. A. Long: Peter Debye – An Appreciation – Science, 24 Feb, 1967: 979-980.
- European Synchrotron Radiation Facility: Historical Notes on Peter Debye.
- ChemViews: 50th Anniversary: Death of Peter Debye – ChemViews Magazine, 02 November 2016.