My readers have been so familiarized with the fact that it requires at
least five planets to attack every one of a square arrangement of
sixty-four stars that many of them have, perhaps, got to believe that a
larger square arrangement of stars must need an increase of planets. It
was to correct this possible error of reasoning, and so warn readers
against another of those numerous little pitfalls in the world of
puzzledom, that I devised this new stellar problem. Let me then state at
once that, in the case of a square arrangement of eighty one stars,
there are several ways of placing five planets so that every star shall
be in line with at least one planet vertically, horizontally, or
diagonally. Here is the solution to the "Southern Cross": --
It will be remembered that I said that the five planets in their new
positions "will, of course, obscure five other stars in place of those
at present covered." This was to exclude an easier solution in which
only four planets need be moved.