At Sobral, as has been seen, there were two instru-
ments, the regular 13-inch astrographic lens and the
4-inch auxiliary camera. On account of defects, which
had been discovered in the large codostat mirror, the
14



2IO Gravitation versus Relativity

astrographic lens was stopped down to &-indies aper-
ture. On the morning of the eclipse day the sun was
covered with clouds: at the time of first contact the
sun was invisible. As the eclipse progressed towards
the total stage, however, the clouds diminished, and
during the critical period of totality the region of the
sky in the vicinity of the sun was practically free from
clouds. During the middle of this period, unfortu-
nately, a thin cloud passed over the sun ; not sufficiently
thick to conceal the corona, but heavy enough to pre-
vent photography of the stars. With the astrographic
telescope nineteen (19) plates were taken, with alter-
nate exposures of 5 and 10 seconds; with the 4-inch
camera eight (8) plates were taken, with a uniform
exposure of 28 seconds. When these plates were de-
veloped, it was found that at least seven stars appeared
on sixteen (16) of the plates taken with the large tele-
scope, and upon seven (7) of the plates taken with
the 4-inch camera. The remaining plates, taken
through the thin film of cloud, did not show the
necessary star images.
