es of stars at first supposed to be
beyond its capacity.

[Illustration: Fig. 29. Aldebaran, the "leader" (of the Pleiades),
was also known to the Arabs as "The Eye of the Bull," "The Heart
of the Bull," and "The Great Camel" (Hubble).

Like Betelgeuse and Antares, it is notable for its red color, which
accounts for the fact that its image on this photograph is hardly
more conspicuous than the images of stars which are actually much
fainter but contain a larger proportion of blue light, to which
the photographic plates here employed are more sensitive than to
red or yellow. Aldebaran is about 50 light-years from the earth.
Interferometer measures, now in progress on Mount Wilson, indicate
that its angular diameter is about 0.020 of a second.]

While the theory of dwarf and giant stars and the measurements just
described afford no direct evidence bearing on Laplace's explanation
of the formation of planets, they show that stars exist which are
comparable in diameter with our solar system, and suggest that the
sun must have shrunk from vast dimensions. The mode of formation
of systems like our own, and of other systems numerously illustrated
in the heavens, is one of the most fascinating problems of astronomy.
Much light has been thrown on it by recent investigations, rendered
possible by the development of new and powerful instruments and by
advances in physics of the most fundamental character. All the
evidence confirms the existence of dwarf and giant stars, but much
work must be done before the entire course of stellar evolution
can be explained.

CHAPTER III

COSMIC CRUCIBLES

"Shelter during Raids," marking the entrance to underground passages,
was a sign of common occurrence and sinister suggestion throughout
London during the war. With characteristic ingenuity and craftiness,
ostensibly for purposes of peace but with bomb-carrying capacity
as a prime specification, the Zeppelin had been developed by the
Germans to a point where it seriously threatened both London and
Paris. Searchlights, range-finders, and anti-aircraft guns, surpassed
by the daring ventures of British and French airmen, would have
served but little against the night invader except for its one
fatal defect--the inflammable nature of the hydrogen gas that kept
it aloft. A single explosive bullet served to transform a Zeppelin
into a heap of scorched and twisted metal. This characteristic
of hydrogen caused the failure of the Zeppelin