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Judging Einstein

Before most physicists would believe the claims of relativity, they required proof—which would come in the form of a solar eclipse

J. Donald Fernie

Weighing the Data

Many months later, back in England, Eddington pondered the inconsistent results. Einstein's theory predicted a displacement of 1.75 arcseconds, but none of the experiments was in perfect agreement with the theory. The usable photos from Principe showed an average difference of 1.61±0.30 arcseconds, the astrograph in Brazil indicated a deflection of about 0.93 arcseconds (depending on how one weighted the individual spoiled photos), and the little 10-centimeter telescope gave a result of 1.98±0.12 arcseconds. The smaller device, in addition to yielding the most precise data, afforded a wider field of view and supported Einstein's theory of how the displacement should vary with angular distance from the edge of the Sun. But the validation of relativity required exact measurements, particularly because physicists had realized that Newtonian theory alone could predict a stellar displacement that was half that of Einstein's, or about 0.83 arcseconds.

Eventually, Eddington, after much discussion with Dyson, suggested an overall measurement of 1.64 arcseconds, which he took to be in pretty good agreement with Einstein, but he also gave the separate results from each telescope so others might weight them as they saw fit. Moreover, Dyson offered to send exact contact copies of the original photographic glass plates to anyone who wished to make their own measurements, which should have gone far to refute the occasional allegation that Eddington had cooked the results.

Ironically, confirmation of Eddington's conclusion (and the theory of relativity) came from Campbell's team at an eclipse in Australia in 1922, for which they determined a stellar displacement of 1.72±0.11 arcseconds. Campbell had been open in his belief that Einstein was wrong, but when his experiment proved exactly the opposite, good scientist that he was, Campbell immediately admitted his error and never opposed relativity again.

I am indebted to Dr. Jeffrey Crelinsten for granting access to his unpublished work on this topic and for providing comments on an earlier version of this article.

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