playing that pawn, or piece, you discover a check upon your adversary's king, and consequently may often get a piece, or some other advantage by it. Suppose the black king on 6, a white bishop on 41, and a pawn on 34; by moving the pawn to 26, a check by the white bishop is discovered upon the black king.
18. Never guard an inferior piece or pawn with a better, if you can do it with a pawn, because that better piece may in such a case be, as it were, out of play.
19. A pawn pushed on, and well supported, often costs the adversary a piece ; but one separated from the others is seldom of any value. And whenever you have gained a pawn, or other advantage, and are not in danger of losing the move thereby, make as frequent exchanges as you can.
20. If each player have three pawns upon the board, and no piece, and you have a pawn on one side of the board, and the other two on the other side, and your adversary's three are opposite to your two, march with your king to take his pawns ; and if he move to support them, go on to queen with your single pawn; and if he attempt to hinder it, take his pawns, and push yours to queen ; that is, to move a pawn into the adversary's back row, in order to make a queen, when the original is lost.
21. At the latter end of the game, each party having only three or four pawns on different sides of the board, the kings are to endeavour to gain the move, in order to win the game : For example: the white king placed on 54, and the black king on 37, white would gam the move by playing to 53, or black to 38, and in both cases the adverse king would be prevented from advancing.