'Les Vepres Siciliennes,' which was produced in Paris in 1855, during the Universal Exhibition, only achieved a partial success, and 'Simon Boccanegra' (1857), even in the revised and partly re-written form which was performed in 1881, has never been popular out of Italy. 'Un Ballo in Maschera' (1861), on the other hand, was for many years a great favourite in this country, and has recently been revived with remarkable success. The scene of the opera is laid in New England. Riccardo, the governor of Boston, loves Amelia, the wife of his secretary, Renato. After a scene in a fortune-teller's hut, in which Riccardo's death is predicted, the lovers meet in a desolate spot on the seashore. Thither also comes Renato, who has discovered a plot against his chief and hastens to warn him of his danger. In order to save Riccardo's life Renato resorts to the time-honoured device of an exchange of cloaks. Thus effectually disguised Riccardo makes his escape, leaving Amelia, also completely unrecognisable in a transparent gauze veil, in charge of her unsuspecting husband, who has promised to convey her home in safety. Enter the conspirators, who attack Renato; Amelia rushes between the combatants, and at the psychological moment her veil drops off. Tableau and curtain to a mocking chorus of the conspirators, which forms a sinister background to the anguish and despair of the betrayed husband and guilty wife. In the next act Renato joins forces with the conspirators, and in the last he murders Riccardo at the masked ball from which the opera takes its name. 'Un Ballo in Maschera' is one of the best operas of Verdi's middle period. Like 'Rigoletto' it abounds in sharp and striking contrasts of character, the gay and brilliant music of the page Oscar, in particular, forming an effective foil to the more tragic portions of the score. The same feeling for contrast is perceptible in 'La Forza del Destino,' in which the gloom of a most sanguinary plot is relieved by the humours of a vivandiere and a comic priest. This work, which was produced at St. Petersburg in 1862, has never been popular out of Italy, and 'Don Carlos,' which was written for the Paris Exhibition of 1867, seems also to be practically laid upon the shelf. It tells of the love of Don Carlos for his stepmother, Elizabeth, the wife of Philip II. of Spain, and apart from the dulness of the libretto, has the faults of a work of transition. Verdi's earlier manner was beginning to lie heavily upon his shoulders, but he was not yet strong enough to sever his connection with the past. There are scenes in 'Don Carlos' which foreshadow the truth and freedom of 'Aida,' but their beauty is often marred by strange relapses into conventionality.