In 1947, F. V. Morley invented this variant, and wrote about this variant,
in a book titled My One Contribution to Chess. The description here
is based on the information in Pritchard's
Encyclopedia of Chess.
The game is played on a board, with at each of the four sides, a corridor
of six squares added. The opening setup is otherwise unchanged.
The rule description is unclear on where pawns promote. To keep as close
as possible to orthodox chess, one can promote pawns on the squares where
in opening setup the opponents non-pawn pieces are located. Other rules
are as in orthodox chess. Pawns can get stuck in a corner, where there only
hope of moving is taking a hostile piece.
Another variant
Another variant on a board with enlarged sides is also attributed to
Morley. Here, the board has the following shape (displayed with opening
setup.)
