38 years. For some years thereafter, the only performers of the roles were another husband–wife team, Heinrich Vogl and Therese Vogl. Performance history The next production of Tristan was in Weimar in 1874. Wagner himself supervised another production of Tristan in Berlin in March 1876, but the opera was only performed in his own theatre at the Bayreuth Festival after his death; Cosima Wagner, his widow, oversaw this in 1886, a production that was widely acclaimed. The first production outside of Germany was given at the Theatre Royal, Drury Lane, London in 1882; Tristan was performed by Hermann Winkelmann, who later that year sang the title role of Parsifal at Bayreuth. It was conducted by Hans Richter, who also conducted the first Covent Garden production two years later. Winkelmann was also the first Vienna Tristan, in 1883. The first American performance was held at the Metropolitan Opera in December 1886, conducted by Anton Seidl. Significance in the development of romantic music The score of Tristan und Isolde has often been cited as a landmark in the development of Western music. Throughout the opera, Wagner uses a remarkable range of orchestral colour, harmony, and polyphony, doing so with a freedom rarely found in his earlier operas. The very first chord in the piece, the Tristan chord, is of great significance in the move away from traditional tonal harmony as it resolves to another dissonant chord: The opera is noted for its numerous expansions of harmonic practice; for instance, one significant innovation is the frequent use of two consecutive chords containing tritones (diminished fifth or augmented fourth), neither of which is a diminished seventh chord (F–B, bar 2; E–A-sharp, bar 3). Tristan und Isolde is also notable for its use of harmonic suspension – a device used by a composer to create musical tension by exposing the listener to a series of prolonged unfinished cadences, thereby inspiring a desire and expectation on the part of the listener for musical resolution. While suspension is a common compositional device (in use since before the Renaissance), Wagner was one of the first composers to employ harmonic suspension over the course of an entire work. The cadences first introduced in the prelude are not resolved until the finale of Act III, and, on a number of occasions throughout the opera, Wagner primes the audience for a musical climax with a series of chords building in tension