I N T R O D U C T I O N T O V O L U M E 9 x x x i i i
Even though by June 1917 Freundlich was already well aware that this opportu-
nity would be “unusually
the devastating aftermath of the war put an
end to any hope for a German expedition as far afield as South America or Central
Africa, from where the total eclipse of 29 May 1919 would be visible. Britain, as
one of the victorious Allies, was in a slightly better position and mounted not one,
but two expeditions. Already in 1916, Willem de Sitter’s papers in the journal of
the Royal Astronomical Society had focused attention on the observational conse-
quences of general relativity, and had made a distinct impression on the English as-
Arthur S. Eddington (see Illustration 4) immediately be-
gan to study the theory. His own accounts were widely read and highly
In March 1917, the Astronomer Royal, Sir Frank Watson Dyson,
noted that the eclipse of 1919 would be ideal for the test. The Royal Society’s and
Royal Astronomical Society’s Joint Permanent Eclipse Committee (JPEC) formed
a subgroup with the task of planning the expedition. But only with the end of the
war in November 1918 did an expedition actually seem feasible, and shortly there-
after the British astronomers focused their entire efforts on this
Two expeditions were sent. The first consisted of Charles R. Davidson and An-
drew Claude de la Cherois Crommelin, both from Dyson’s own Greenwich Obser-
vatory; the second of Edwin Turner Cottingham and Eddington himself. The
Greenwich pair went to Sobral in northeastern Brazil, taking as their main instru-
ment the 13-inch astrographic lens of the Greenwich Observatory and, as a backup
instrument, a 4-inch telescope obtained on loan from the Royal Irish Academy. Ed-
dington traveled to the island of Principe in the Gulf of Guinea, off the west coast
of Central Africa, equipped with the astrographic lens of the Oxford Observatory.
On 8 March 1919 the two expeditions departed Liverpool on board the S.S.
Anselm, bound for Brazil. Eddington and Cottingham left the ship at Madeira and,
after having to wait for a connecting ship to Principe, arrived on the island on 23
April. The Crommelin expedition reached Sobral at the end of April. Preparations
went ahead at both locations during the month of May.
Upon mounting their equipment, the astronomers at Sobral discovered that the
coelostat mirror used in conjunction with one of their lenses (the astrographic lens)
suffered from serious astigmatism. In order to avoid this astigmatism, they stopped
down the 13-inch aperture to 8 inches. But when they developed the first photo-
graphic plates after the eclipse, they noticed that the images were nevertheless
blurred and apparently out of focus. Having initially contemplated leaving the site
without taking comparison photographs of the same star field and relying instead
on check plates of a neighboring set of stars, they now decided to stay in Brazil. At
Sobral, the eclipse took place in the morning hours. In order to obtain comparison
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