The history of the determination of the velocity of light to the mid twentieth century

Abstract

The thesis looks at the various attempts at measuring the velocity of light from ancient times to 1940. It concentrates on astronomical and optical methods apart from mentioning electrical methods where this was considered necessary in the historical development. In the early part of the study the ancients considered that light travelled faster than sound and controversy aroseas to whether it had a finite or infinite velocity. A brief look is taken at the theories of Alhazen and Roger Bacon before turning to the work of Galileo and his attempts to produce an experimental verification of the finite velocity of light. The experiments of Roemer and the first astronomical verification of the finite nature of the velocity using the satellites of Jupiter are considered in some detail. Here mention is made of the work of Descartes and the independent verification by Bradley in 1729.Next the rival wave and corpuscular theories of light are considered as in trying to explain the phenomena of refraction each theory gave rise to a different value for the velocity of light as it travelled through a more dense transmitting medium. Thus the velocity of light became a crucial factor in deciding which theory had more merit. Wheatstone's use of a revolving mirror to measure small time intervals is mentioned as well as the Fizeau method on comparing the velocity of light in air and water. The main part of the thesis concentrates on the various terrestrial optical methods of the nineteenth century starting with the experiments of Foucault, Cornu and Fizeau. The work of Young and Forbes is given in detail since their series of experiments were made so that each observation was to be an accurate measurement of the velocity. The classic experiments of Michelson spanning 1879 - 1930 are considered in detail as well as mentioning the work of Newcomb and Perrotin. The work of de Bray is mentioned along with a comparison of modern determinations. The concluding chapter draws attention to the emergence of the 'experimental method in Renaissance times and the requirement of progress in scientific technology before accurate measurements can be taken. The transition from the single scientist working in isolation developing into the team effort as is common practice today is also mentioned.