---
title: "Eddington experiment"
chunk: 3/5
source: "https://en.wikipedia.org/wiki/Eddington_experiment"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T03:39:05.943562+00:00"
instance: "kb-cron"
---

=== Príncipe ===
The equipment used for the expedition to Príncipe, an island in the Gulf of Guinea off the coast of West Africa, was an astrographic lens borrowed from the Radcliffe Observatory in Oxford. Eddington sailed from England in March 1919. By mid-May he had his equipment set up on Príncipe near what was then Spanish Guinea. The eclipse was due to take place in the early afternoon of 29 May, at 2 pm, but that morning there was a storm with heavy rain. Eddington wrote: The rain stopped about noon and about 1.30 ... we began to get a glimpse of the sun. We had to carry out our photographs in faith. I did not see the eclipse, being too busy changing plates, except for one glance to make sure that it had begun and another half-way through to see how much cloud there was. We took sixteen photographs. They are all good of the sun, showing a very remarkable prominence; but the cloud has interfered with the star images. The last few photographs show a few images which I hope will give us what we need ... Eddington developed the photographs on Príncipe, and attempted to measure the change in the stellar positions during the eclipse. On 3 June, despite the clouds that had reduced the quality of the plates, Eddington recorded in his notebook: "... one plate I measured gave a result agreeing with Einstein."
British future astronomer and astrophysicist Cecilia Payne-Gaposchkin attended Eddington's lectures at Cambridge (including one where Eddington discussed the results of the eclipse expeditions) and later related how strongly these lectures had affected her.

== Results and publication ==

The results were announced at a joint meeting of the Royal Society and Royal Astronomical Society in November 1919, and published in the Philosophical Transactions of the Royal Society in 1920. Following the return of the expedition, Eddington was addressing a dinner held by the Royal Astronomical Society, and, showing his more light-hearted side, recited the following verse that he had composed in a style parodying the Rubaiyat of Omar Khayyam: 

== Later replications ==
The light deflection measurements were repeated by expeditions that observed the total solar eclipse of 21 September 1922 in Australia. An important role in this was played by the Lick Observatory and the Mount Wilson Observatory, both in California, US. On 12 April 1923, William Wallace Campbell announced that the preliminary new results confirmed Einstein's theory of relativity and prediction of the amount of light deflection with measurements from over 200 stars. Final results published in 1928 used measurements of over 3,000 star images.

== Reception ==