throughout the structure which will act as centers of
condensation, drawing surrounding materials into combination
with them. The processes of growth from nuclei originally small
to volumes and masses ultimately stupendous must be slow at
first, relatively more rapid after the masses have grown to
moderate dimensions and the supplies of outlying materials are
still plentiful, and again slow after the supplies shall have
been largely exhausted. By virtue of motions prevailing within
the original nebular structure, or because of inrushing
materials which strike the central masses, not centrally but
obliquely, low rotations of the condensed nebulous masses will
occur. Stupendous quantities of heat will be generated in the
building-up process. This heat will radiate rapidly into space
because the gaseous masses are highly rarefied and their
radiating surfaces are large in proportion to the masses. With
loss of heat the nebulous masses will contract in volume and
gradually assume forms more and more spherical. When the forms
become approximately spherical, the first stage of stellar life
may be said to have been reached.

It was Herschel's belief that by processes of condensation,
following the loss of heat by radiation into surrounding space,
formless nebulae gravitated into nebula of smaller and smaller
volumes until finally the planetary form was reached, and that
planetaries were the ancestors of stars in general. That the
planetaries do develop into stars, we have every reason to
believe; but that all nebulae, or relatively many nebulae, pass
through the planetary stage, or that many of our stars have
developed from planetaries, we shall later find good reason for
doubting. The probabilities are immensely stronger that the