This instrument was attached to the eye piece of the
telescope, and the image of the eclipse reduced to such a size that the
moon just fitted into the aperture of the V, while opposite sides of the
corona were reflected through the prisms to the place where they came
together. In this way both sides of the corona were seen through the
eye-piece at the same time. On looking at the eclipse this is what Dr.
Hastings saw: The light of the corona was divided into its constituents.
Prominent among them was a bright green line, which is designated by the
number 1,474; to this line attention was directed. Its presence in the
spectrum has been an argument in favor of the view that the corona is
a solar atmosphere. If this is the case, the line should remain fixed
during the eclipse; but if the corona is due to diffraction, this line
should change. It should grow shorter in the light from one side of the
corona, and longer on the other. The observation was now reduced to
watching for a change in the relative length of two green lines.
At the beginning of totality the line from the west side was much the
longer, but as the eclipse progressed it shortened notably, while the
line from the east side, shorter by about one-third at the beginning of
the eclipse, grew longer.
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