Cy-pres doctrine preserves charitable intention by allowing substitution of an alternative mode when prescribed mode fails. The cy-pres doctrine permits courts to substitute a mode of charitable application when a donor's prescribed mode is incapable of performance but a broader charitable intention exists; where the prescribed mode was the essence of the donor's intention the court has no power to substitute, and cy-pres applies only to gifts charitable in law and may govern any surplus not exhausted by the particular mode.