Class B to the Class M, and the color changes from blue to
extreme red, because the violet and blue radiations become
rapidly weaker as we pass through the various classes.

GENERAL COURSE OF EVOLUTIONARY PROCESS

The general course of the evolutionary processes as applied to
the principal classes of celestial bodies is thought to be
fairly well known. With very few exceptions astronomers are
agreed as to the main trend of this order, but this must not be
interpreted to mean that there are no outstanding differences
of opinion. There are, in fact, some items of knowledge which
seem to run counter to every order of evolution that has been
proposed.

The large irregular nebulae, such as the great nebula in Orion,
the Trifid nebula, and the background of nebulosity which
embraces a large part of the constellation of Orion, are
thought to represent the earliest form of inorganic life known
to us. The material appears to be in a chaotic state. There is
no suggestion of order or system. The spectroscope shows that
in many cases the substance consists of glowing gases or
vapors; but whether they are glowing from the incandescence
resulting from high temperature, or electrical condition, or
otherwise, is unknown, though heat origin of their light is the
simplest hypothesis now available. Whether such nebulae are
originally hot or cold, we must believe that they are endowed
with gravitational power, and that their molecules or particles
are, or will ultimately be, in motion. It will happen that
there are regions of greater density, or nuclei, here and there