No. 8.

BLACK.
+---+---+---+---+---+---+---+---+
| | | | | R*| K*| | R*|
+---+---+---+---+---+---+---+---+
| | P*| B*| | Q*| | P*| P*|
+---+---+---+---+---+---+---+---+
| P*| | N*| | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | B*| | | |
+---+---+---+---+---+---+---+---+
| | B | Q | | | | | |
+---+---+---+---+---+---+---+---+
| P | P | P | | | | P | P |
+---+---+---+---+---+---+---+---+
| R | | B | | K | | | R |
+---+---+---+---+---+---+---+---+
WHITE.

In this situation the white King is threatened with what is called "a
discovered check," that is, his opponent, by removing the Bishop, would
_discover_ check from the Queen, a proceeding in the present instance,
which would speedily involve the loss of the game to White. Not being
at the moment in check, however, and having moved neither King nor Rook,
and there being no _intervening_ Piece between the King and his own
Rook, White is enabled to castle, giving check to the adverse King at