Page:Popular Science Monthly Volume 1.djvu/162

152 as an opaque layer—the umbras of spots. A cloud once formed in this manner acts as a screen toward the higher regions; hence a secondary cooling effect in those regions also, and the formation of another cloudy layer, less dense—the penumbra.

The speculations of M. Faye upon this subject have also attracted some attention. He assumes the sun to be still in a gaseous state. The photosphere he regards as consisting of clouds which are the simple consequence of cooling, and looks upon it, in fact, as the limit which