Robert John Strutt, fourth Baron Rayleigh: a brief tribute

Abstract

Robert John Strutt, (1 875 — 1 947), fig. I was an experimental physicist of such exceptional skill and ingenuity in optics that, had he lived today, he would undoubtedly have made significant contributions to the fields of laser physics and laser spectroscopy. Eldest son of the Nobel laureate John William Strutt, third Baron Rayleigh (1 842 — I 91 9, Nobel prize I 904 together with Sir William Ramsay for the isolation of argon), he enrolled for the Natural Science Tnpos at Cambridge in 1894, completing both parts with first class honours before commencing research at the Cavendish Laboratory under Sir J. J. Thomson (Nobel prize I 906 for the discovery of the electron). Rapid progress and publication in his earliest fields of research, electrical discharges in gases and radioactivity, ensured his election as a Fellow of the Royal Society in I 905, 'at the exceptionally early age of 29', and he was one of the first (1 904), after Rutherford, to publish a book on the new field of radioactivity, i.e. Nuclear Physics at its inception1'2. A striking demonstration of the charge carried by /3 -rays was invented by Strutt, and shown at the family home (Terling Place in Essex, figs. 2 and 3) to both Ernest Rutherford and Lord Kelvin, the latter being 'wildly enthusiastic' at seeing a process which appeared to him to violate the Second Law of Thermodynamics1. Later dubbed Rayleigh's radioactive clock, this was an ingenious modification of the gold-leaf electroscope to incorporate radioactive samples of different concentration. In these early years, Strutt also provided the spectroscopic evidence that the radioactivity released in the natural springs in Bath in fact yielded the newly isolated atmospheric constituent helium (1904). A later discovery (1906), that the radium embedded in the earth's crust released sufficient thermal energy to account for the temperature gradient observed near the surface, was instrumental in overturning Lord Kelvin's calculation (1862) of the age of the Earth, and in bnnging the physical picture much closer to that provided by geological evidence (some 4 billion years).