Soon after, Dr. David
Gill, at the Cape observatory, made fine photographs of a comet, and the
flecks of starlight on his plates first suggested the possibilities of
this method in charting the heavens.

Since then star-charting with the film has come virtually to supersede
the old method. A concerted effort is being made by astronomers in
various parts of the world to make a complete chart of the heavens, and
before the close of our century this work will be accomplished, some
fifty or sixty millions of visible stars being placed on record with a
degree of accuracy hitherto unapproachable. Moreover, other millions of
stars are brought to light by the negative, which are too distant or
dim to be visible with any telescopic powers yet attained--a fact
which wholly discredits all previous inferences as to the limits of
our sidereal system. Hence, notwithstanding the wonderful instrumental
advances of the nineteenth century, knowledge of the exact form and
extent of our universe seems more unattainable than it seemed a century
ago.

The Structure of Nebulae

Yet the new instruments, while leaving so much untold, have revealed
some vastly important secrets of cosmic structure. In particular, they
have set at rest the long-standing doubts as to the real structure and
position of the mysterious nebulae--those lazy masses, only two or
three of them visible to the unaided eye, which the telescope reveals
in almost limitless abundance, scattered everywhere among the stars,
but grouped in particular about the poles of the stellar stream or disk
which we call the Milky Way.

Herschel's later view, which held that some at least of the nebulae are
composed of a "shining fluid," in process of condensation to form stars,
was generally accepted for almost half a century. But in 1844, when
Lord Rosse's great six-foot reflector--the largest telescope ever yet
constructed--was turned on the nebulae, it made this hypothesis seem
very doubtful. Just as Galileo's first lens had resolved the Milky Way
into stars, just as Herschel had resolved nebulae that resisted all
instruments but his own, so Lord Rosse's even greater reflector resolved
others that would not yield to Herschel's largest mirror. It seemed
a fair inference that with sufficient power, perhaps some day to be
attained, all nebulae would yield, hence that all are in reality what
Herschel had at first thought them--vastly distant "island universes,"
composed of aggregation