6. The visual double stars afford strong evidence that the
order of evolution described is correct. The 36-inch refractor
has shown that one star in 18, on the average, brighter than
the ninth visual magnitude, consists of two or more suns which
we can not doubt are in slow revolution around each other. The
number of double stars observable would be very much greater
than this if they were not so far away. Of the 20 stars which
we say are our nearest neighbors, 8 are well known double
stars; one double in each two and one half, on the average.
Aitken has made a specialty of observing the double stars whose
components in each case are very close together and are in
comparatively rapid revolution. His program includes 164 such
systems whose types of spectra are known, as in the following
table:
title=Syracuse
