Heather Harper, one of the most recorded singers of her time, made an extraordinary transition from a lyric soprano in the English pastoral tradition to a spinto-weight artist of great power and authority. While her earliest appearances and recordings brought to mind such other singers as Isobel Baillie and Jennifer Vyvyan, her prime years showed a voice that had grown in size and roundness while retaining its initial flexibility. Many critics have opined that her 1966 recording of Handel's Messiah remains unequaled. While she chose to avoid most of the Italian spinto repertor...