Along with the media and scientific publication inherent to the expedition to the observation of the solar eclipse of the 29th of May of 1919, Eddington’s presence on the island of Principe for this purpose, and in particular his stay at Roça Sundy, was documented by him in letters addressed to his mother and sister.

What did Eddington see?

In this communication we aim to present a possible modulation of iconic sceneries  through which Eddington went, founded on the integration of arguments from the History of Science, Mathematics and Architecture. The virtual visit to these sceneries is part of a scientific education experiment which, throughout the route in the island of Príncipe, invites the visitor to interact with different dimensions of knowledge and the local reality.

The photographs taken during the eclipse by the British expeditions to Príncipe island and Sobral in Brazil showed the order of magnitude in the light deviation that concorded with Einstein’s general relativity. The quality of the photographic plates was critical for the argument published in the Philosophical Transactions article and its authors invited other astronomers to apply for copies to ‘assure themselves’ of this quality.

Today copies of these epoch-making British pictures are to be found in many places around the world, for instance in the Landessternwarte Heidelberg-Königstuhl (Heidelberg), the Niels Bohr Institute (Copenhagen), and in several more places. Some of the images are copies from Sobral others from Príncipe, some are on paper others on glass plates. What stories does each of these copies tell? Can the circulation pattern of these pictures teach us anything about the appropriation of the eclipse results by further scientists in different local and national contexts?

The observations of the total solar eclipse made by the Royal Society expeditions of 1919 are one of the greatest experiments in physics.nThe observations from the two expeditions (to Sobral and to Principe) were made in different meteorological conditions, with different instruments and at different local times. This led to datasets of different quality and sizes that required different data analysis procedures. We revisit the original paper by Dyson, Eddington and Davidson published in the Philosophical Transactions of the Royal Society in 1920, with two goals in mind. On one hand, we examine the two data analyses procedures presenting a comparison of the two methods. The data from Principe was analysed in an ingenious way, making use of external data, trying to make the most of a small dataset. The larger dataset from Sobral was analysed in a more standard manner and provided the strongest constraint on the deflection of light at the Sun’s limb (1.9800±0.1200). The paper, however, does not detail the method used to compute the error. This leads to our second goal: to make a new computation of the uncertainties using the data available in the paper. For this, we carried out a Fisher matrix computation in a four-dimensional parameter space and found a consistent tighter constraint of (1.9600 ± 0.0600).

The success of the 1919 eclipse expeditions relied to a great extent on a network of laborers who organized, managed, and made those expeditions possible, and whose work often passed unnoticed. This paper aims to study those networks animated by the eclipse committees established in Portugal and Brazil. Among other activities, those committees played an intermediary role between the British astronomical teams, the local governments, social elites, and colonial representatives (in the case of Portugal). A comparative view of the role of the Portuguese and Brazilian eclipse committees provides an insight into different invisible laborers, from the local worker who carried the instruments to the member of Parliament who smoothed the travels of foreign astronomers (in the case of Brazil), as well as into the invisible (logistics’) labor of the local astronomers who led the eclipse committees. In the process, it sheds new light on the Brazilian and Portuguese scientific communities.

Break and Refreshments

This paper addresses the legendary total solar eclipse of 29 May 1919. Two British teams confirmed the light bending prediction by Albert Einstein: Charles R. Davidson and Andrew C. C. Crommelin in Sobral, Brazil and Arthur S. Eddington and Edwin T. Cottingham on the African island of Príncipe, then part of the Portuguese empire.

By jointly analyzing the two astronomical expeditions supported by written and visual sources, I show how, despite extensive scholarship on this famous historical episode and the historiographical emphasis on the plural dimensions of knowledge construction, many human and non-human actors have been kept in the shadow of the eclipse. I do so by focusing on what I call knowledge from the periphery together with knowledge from below, grounded literally on how localities (sites) affect choices and events, and growing outward to encompass a wide range of participants. I show how the geopolitical status of the two nations where the observational sites were located, and specifically Portugal’s condition of colonial power, affected main decisions and events, while highlighting the active role of participants, ranging from experts from the peripheries and those involved in the travels to local elites and anonymous peoples, some of whom contributed to the observation of totality.

This presentation intends to share preliminary research regarding the 1912 Eclipse expeditions to Passa-Quatro, Brazil. An emblematic group photo, taken by the photographer Augusto Soucasoux on the occasion of this eclipse, will serve as a mechanism to map the expeditions, actors and agendas present. Properly characterising the 1912 expeditions is relevant to better understand the 1919 expeditions. Not only did the previous experience informed the planning of the latter but, comparing both endeavours enables us to understand in which ways the particular geopolitical circumstances, in place in 1919, influenced the planning of the expeditions. Finally, it is also the purpose of this presentation to demonstrate the relevance of the information mobilised and extracted from a visual source.

Final words by the E3GLOBAL project’s Scientific Coordination