fairly definite conception of the arrangement of the sidereal system evolves
naturally from the observational work
We find, in short, that globular
clusters, though extensive and massive structures, are but subordinate
items in the immensely greater organization which is dimly outlined by
their positions. From the new point of view our galactic universe appears
as a single, enormous, all-comprehending unit, the extent and form of
which seem to be indicated through the dimensions of the widely extended
assemblage of globular clusters. The adoption of such an arrangement leaves
us with no evidence of a plurality of stellar 'universes.' Even the remotest
of recorded globular clusters do not seem to be independent organizations.
The hypothesis that spiral nebulae are separate galactic systems now meets
with further difficulties.
So long as the diameter of the galactic
system was thought to be only a thousand light-years or so, we had a fairly
plausible case for the "island universe" hypothesis. But
any external 'universe' must now be compared with a galactic system probably
more than three hundred thousand light-years in diameter.