A text-book of general astronomy : for colleges and scientific schools (1888)
Young, Charles A. (Charles Augustus), 1834-1908 · Boston ; London : Ginn & Company · leaf 198
on one side, and the peuumbral … Fig. 97. —A Normal Sun Spot. (Secchi; modified.) filaments, instead of being strictly radial, are frequently distorted inevery conceivable way. In fact, the normal spots form a very smallproportion of the whole number. The darkest portions of the umbra are dark only by contrast.Photometric…
Astronomy
Internet Archive · Wellesley College Library · Public Domain Mark 1.0. Free to use for anything.
