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History of Science, a — Volume 3 by Henry Smith Williams;Edward Huntington Williams
page 86 of 354 (24%)
bears the same relation to the speculative thought of
our time that the nebular hypothesis of Laplace bore
to that of the eighteenth century. Outlined in a few
words, it is an attempt to explain all the major phenomena
of the universe as due, directly or indirectly, to
the gravitational impact of such meteoric particles, or
specks of cosmic dust, as comets are composed of. Nebulae
are vast cometary clouds, with particles more or
less widely separated, giving off gases through meteoric
collisions, internal or external, and perhaps glowing also
with electrical or phosphorescent light. Gravity eventually
brings the nebular particles into closer aggregations,
and increased collisions finally vaporize the entire
mass, forming planetary nebulae and gaseous stars.
Continued condensation may make the stellar mass
hotter and more luminous for a time, but eventually
leads to its liquefaction, and ultimate consolidation--
the aforetime nebulae becoming in the end a dark or
planetary star.

The exact correlation which Lockyer attempts to
point out between successive stages of meteoric condensation
and the various types of observed stellar bodies
does not meet with unanimous acceptance. Mr.
Ranyard, for example, suggests that the visible nebulae
may not be nascent stars, but emanations from stars,
and that the true pre-stellar nebulae are invisible until
condensed to stellar proportions. But such details
aside, the broad general hypothesis that all the bodies
of the universe are, so to speak, of a single species--
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