Page:A Short History of the World.djvu/27

Photo: Prof. Hale.

A DARK NEBULA

Taken in 1920 with the aid of the largest telescope in the world. One of the first photographs taken by the Mount Wilson telescope.
There are dark nebulæ and bright nebulæ. Prof. Henry Norris Russell, against the British theory, holds that the dark nebulæ preceded the bright nebulæ