In 1911, an astronomer at the Berlin Observatory named Erwin Findlay-Freundlich had been working on experimentally proving Einstein’s new theory on the deflection of light due to gravity. Freundlich initially attempted to use existing photographs of total solar eclipses to measure the deflection of light, but these were insufficient. He, therefore, decided to enlist help from an American astronomer, Charles D. Perrine, in capturing new photos from the total eclipse of October 10, 1912. 

Perrine, at this point, was the director of the Argentine National Observatory (now known as the Astronomical Observatory of Córdoba). He had built quite a reputation while working at the Lick Observatory in California, having discovered Jupiter’s sixth and seventh moons in 1904 and 1905 with the help of photography. This achievement was truly significant – since Galileo discovered the first four moons almost 300 years before Perrine’s accomplishment as only one other moon had been detected since then.

With a large part of the path of totality of the 1912 eclipse crossing over Brazil, expedition groups from across the globe travelled to this country to view the eclipse. These included the Argentinian, British, French, Brazilian, and Chilean parties. Charles D. Perrine led the Argentinian expedition, which was the only group with measuring the deflection of light planned as one of their objectives. 

The British were astronomers from the Greenwich Observatory, who planned to study the structure of the solar corona by taking photographs during the eclipse. They also planned to use the photographs to learn about the distribution of “coronium”, thought to be a new element at the time but later discovered to be highly ionised iron. An agenda of this sort was common for all expeditions, as the study of the corona and the magnetic effects of eclipses were the dominant themes of the time. The British, Brazilian, and French groups set up on the same site at Pasa Quatro, whereas the Argentinean and Chilean groups set up about 50 miles away at Cristina. 

Arthur Stanley Eddington, a British astronomer working for the Royal Observatory, wrote in a series of letters to his mother about the great hospitality he and his team received in Brazil. The Brazilian government paid for their train travel and provided courtesy at customs when importing their equipment. The government even covered the expenses for them to watch a cinematograph performance. Furthermore, the observers were fortunate enough to be able to explore parts of Brazil when they weren’t caught up in the preparation of the observation site. It took days to construct the huts, and the team had to set up equipment and repeat practice drills for the eclipse event too.

Despite the luxuries, Eddington also raised many complaints about his trip to Brazil. Their luggage had initially been mixed up and he believed that a case had been lost. Two individuals were sent to assist Eddington, but he became annoyed once he realised they couldn’t speak English or French.  Language barriers in particular were a repeating theme for Eddington. After the eclipse, he attended a banquet with the president of Brazil, but couldn’t understand the speeches since they were in Portuguese. He ended up mostly only talking to the secretary of the American embassy for the whole event.

The British astronomer also complained of the contribution of a few unnamed individuals who he found to be of little use throughout his letters, and repeatedly mentioned two individuals from the French expedition “Lee & Worthington” who “were detested by everyone”. On the other hand, Eddington praised the assistance of many locals who had helped the observers during the eclipse and overall expedition and would give many named thanks in the final expedition report. It is in his letters (which you can find in the ‘Further Reading’ section below) that we get insight into how the small individual contributions from perhaps hundreds of people in any given eclipse expedition go unheard of in history. 

At Pasa Quatro, the focus for the day of the eclipse was on the visit of the Brazilian president, the foreign minister, and the American ambassador, as well as the press which inevitably followed. Almost a thousand people had travelled to Pasa Quatro to observe the eclipse. Tragically, for both the spectators and the astronomers, observations were entirely unsuccessful as “The rain became heavier as totality drew near; it was not until 5 minutes before totality that the darkness increased noticeably, then it came on very rapidly. It was extremely dark for the time of totality—one could just see one’s watch with difficulty. As soon as it was over it grew lighter very quickly.” 

Some were able to make measurements of terrestrial magnetism and atmospheric electricity, and a local volunteer, Pierre Seux, counted the duration of totality. The expedition parties also had to delay dismantling and packing their equipment and huts, due to the overwhelming amount of mud that made it difficult to even walk in. 

The first successful observation of the deflection of light wouldn’t occur until 1919, and this would be a feat achieved by a team from the Greenwich Observatory. Interestingly though, at the time of the 1912 eclipse, Einstein’s prediction was actually incorrect! The now-accepted theory on the deflection of light didn’t emerge until 1915 and a correction of a missing factor of 2 was made in 1916. What would’ve happened were the experiment to have been successful in 1912 can only be left to the imagination, but one could no doubt imagine it having a profound impact on physics, for better or for worse.