x x x i v I N T R O D U C T I O N T O V O L U M E 9
plates with a similar scale, the astronomers would have to wait for an additional
month after the eclipse, when the Hyades star field would become visible in the
night sky at the same altitude.
On Principe, where totality occurred in mid-afternoon, Eddington would have
had to wait for several months for the eclipse star field to be visible at night at the
same altitude. Therefore, in late May, he took check plates of a star field near Arc-
turus to be used for comparison with plates of that same field, and with plates of
the eclipse field taken at Oxford before departure.
As he awaited the expeditions’ results, Einstein surmised on 19 August 1919
(Doc. 93) that the reason for the delay in making an announcement was that the
British astronomers “may be waiting about half a year in order to take comparison
exposures of the relevant sky region with the same instrument.” As it turned out,
the principal reason for the delay between the eclipse and the announcement of the
results was the complexity of the data reduction and analysis.
The British expedition is first mentioned in the correspondence presented in this
volume in a letter to Einstein of 9 April 1919 (Doc. 19) in which Arnold Berliner,
the editor of Die Naturwissenschaften, reports on an article by Crommelin that had
appeared in Nature the previous month, describing the aims of the eclipse expedi-
tion. Einstein and his colleagues in Germany may have been aware of plans for an
English expedition as early as late 1917, following an article in Die Naturwissen-
schaften that gave details of the eclipse and of the British
The widely read
journal repeatedly published brief notes and summaries of articles from British sci-
entific journals. In any case, the upcoming event and the planned observations are
mentioned by Einstein both in his university lectures and in popular
29 May, Einstein, along with many other physicists, anxiously awaited an an-
nouncement of the results.
The first available news was scanty but promising. On 4 June, Eddington, in a
telegram to Dyson, reported that conditions had been cloudy but that he was “hope-
ful” of obtaining useful results. The next day, Crommelin informed Dyson in a ca-
ble that no clouds had hindered the observations at
Brief notes appeared
the following day in both the London Times and Nature. A second telegram from
Crommelin, sent after developing the plates, indicated that all stars of interest were
actually visible. But, in addition to the astigmatism detected before the eclipse, he
reported further problems with their main instrument, the astrographic lens. On 10
June a note about the expeditions appeared in a Dutch newspaper, followed three
days later by Dyson’s official report of the telegrams received at a meeting of the
Royal Astronomical
Einstein himself first mentioned the promising initial reports in a letter of 16
June to his mother (Doc. 61), and expected that final results should be available
within six weeks. But for some time, no further news was forthcoming.
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