Page 460 - 89 history of astronomy_opt

stereoscopically, to prove that the red promi-
nences belong to the sun, and not to the
moon. In 1861 he similarly combined two
photographs of a sun-spot, the perspective
effect showing the umbra like a floor at the
bottom of a hollow penumbra; and in one
˜
case the faculA were discovered to be sail-
ing over a spot apparently at some consid-
erable height. These appearances may be
460