W. The king castles with his queen's rook.
18 B. The queen's bishop's pawn two steps. W. The king's pawn one step.*
19 B. The queen's pawn takes the pawn. W. The queen's pawn one move.
20 B. The bishop at his queen's bishop's second
square. W. The knight at his king's fourth square, f
21 B. The king's rook at the white king's bishop's
third square. W. The queen at her king's knight's second square.
* This move is as difficult to comprehend as to be well explained. You are to observe, when you find yourself with a chain of pawns following one another upon one and the same coloured squares, the pawn who has the van should not be abandoned, but must strive to keep his post. Here again observe, that your king's pawn being not in the line with his comrades, your adversary has pushed his queen's bishop's pawn two steps, for two reasons; the first to engage you to push that of your queen forwards, which, in this case, would be always stopped by that of his queen, and thus leaving behind that of your king would render it entirely useless. The second is, to prevent your king's bishop from battering his king's rook's pawn ; therefore it is best to push your king's pawn upon his rook, and sacrifice it; because then your adversary, by taking it, opens a free passage to your queen's pawn, which you are to advance immediately, and sustain, in case of need, with your other pawns, in order to make a queen with it, or draw some other considerable advantage to win the game. His queen's pawn (now become his king's) appears to have the same advantage of having no opposition from your pawns to make a queen ; however, the difference is great, because his pawn being entirely separated from his comrades will always be endangered in his road by a multitude of your pieces all waging war against it.
f It was necessary to play that knight in order to stop his king's pawn, the more becanse this very pawn, in its present situation, stops the passage of his own bishop, and even of his knight.