Petrus van Musschenbroek (1692–1761), man of tribology

Petrus van Musschenbroek was a famous scientist and inventor, natural philosopher, experimental physicist, engineer, instrument builder, experimenter, in the continental Newtonian tradition of Boerhaave and ‘s Gravesande. And: a tribologist. He is one who deserves more fame than he has received so far, and which is well documented in this publication. Van Musschenbroek coined the name tribometer for his device to measure friction in a journal bearing, and some authors rightly refer to this. However, what seems to have remained unnoticed until now is that he also published quantitative results of his friction measurements and tried to arrive at general laws of friction based on them. He reported in detail on friction experiments on sliding, dry as well as lubricated, sliders and journal bearings, a novum in his time, as early as in 1734. When the data from Van Musschenbroek's tables are mapped into graphs, a method which was not in use at that time, two Stribeck curves for journal bearings emerge. Van Musschenbroek's work deserves much more acclaim in the tribology community than it has now.

John Edwin Field. 20 September 1936—21 October 2020

John Field was a brilliant experimental physicist who made major contributions to the physics and chemistry of solids. His research interests spanned a very wide range of topics, most of them involving energetic phenomena. These areas included the strength properties of solids, fracture growth, impact and erosion phenomena, shock physics, reactivity of solids, explosive initiation, lasers, acoustics and medical physics. Within the Physics and Chemistry of Solids Group in the Cavendish Laboratory, he developed the best-equipped high-speed camera facility in any university in Europe, including seven that achieved frame rates in excess of 10 6 frames per second. In addition to the cameras, extensive use was made of ultrasonics, optical and electron microscopy, mass spectroscopy and thermal techniques. He played an important national role in advising the Ministry of Defence on a wide range of topics in energetic phenomena and materials science, which led to practical engineering solutions. He was an outstanding supervisor of doctoral students, who remember him fondly.

Rudolf Ladenburg and the first quantum interpretation of optical dispersion

In 1921, the experimental physicist Rudolf Ladenburg put forward the first quantum interpretation of optical dispersion. Theoretical physicists had tried to explain dispersion from the point of view of quantum theory ever since 1913, when Niels Bohr proposed his quantum model of atom. Yet, their theories proved unsuccessful. It was Ladenburg who gave a breakthrough step toward our quantum understanding of dispersion. In order to understand Ladenburg’s step, I analyze Ladenburg’s experimental work on dispersion prior to 1913, the reasons why the first theories of dispersion after 1913 were not satisfactory, and Ladenburg’s 1921 proposal. I argue that Ladenburg’s early experimental work on dispersion is indispensable to understand his 1921 paper. The specific kind of experiments he performed before 1913, the related interpretative problems, and the way he tried to solve them, led him reapproach the dispersion problem in 1921 in a way that was completely different from the way theoretical physicists had done it before.

New Theories of Nuclear Reactions

Bohr, inspired by Fermi’s discovery of slow neutrons, conceived his theory of the compound nucleus by the end of 1935. He went on to speculate that if the energy of a neutron incident on a nucleus were increased to the fantastically high energy of 1000 million electron volts, the compound nucleus would explode. Using small wooden models Otto Robert Frisch had constructed, Bohr lectured widely on his theory on a trip around the world in the first half of 1937. By then, Russian-born theoretical physicist Gregory Breit and Hungarian-born theoretical physicist Eugene Wigner in Princeton had conceived their fundamentally equivalent theory of neutron+nucleus resonances. Together, their theory and Bohr’s transformed the theory of nuclear reactions. Orso Mario Corbino, Fermi’s mentor, friend, and protector, died on January 23, 1937, at age sixty. Ernest Rutherford, the greatest experimental physicist since Michael Faraday, died on October 19, 1937, at age sixty-six.

James Watson Cronin. 29 September 1931 — 25 August 2016

James (Jim) Cronin had two outstanding careers. The first, in particle physics, included the discovery of CP violation for which he and Val Fitch were awarded the Nobel Prize in 1980. During the second, in cosmic rays, he played a major role in raising the profile of that field, particularly through his leadership in the creation of the Pierre Auger Observatory, the largest cosmic-ray detector ever constructed. He will be remembered for his incisive mind, his modest style, his internationalism and his encouragement of young scientists, as well as for his brilliance as an experimental physicist and data analyst.