Page:The evolution of worlds - Lowell.djvu/43

centre, thinning out at the edge, and when the central nucleus is pronounced, it seems to have a certain globularity not shared by the arms, and more or less detached from them. This appears in those cases where

Nebula ♅ V. 24 Comæ—after Roberts.
Showing globular structure.

they are shown us edgewise, and it has been thought perceptible in the great nebula of Andromeda. The difficulty in establishing the phenomenon comes from the impossibility of both features showing at their best together. For the globularity to come out well, the spiral must be presented to us nearly in the plane of sight; for the spirality, in a plane at right angles to it.