Enough, however, of this excellent but somewhat fatiguing irony; and let me conclude this chapter with a few words about the librettists of the 18th century. The best _libretti_ of Apostolo Zeno, Calsabigi and Metastasio, such as the _Demofonte_, the _Artaserse_, the _Didone_, and above all the _Olimpiade_, have been set to music by dozens of composers. Piccinni, and Sacchini each composed music twice to the _Olimpiade_; Jomelli set _Didone_ twice and _Demofonte_ twice; Hasse wrote two operas on the _libretto_ of the _Nittetti_, two on that of _Artemisia_, two on _Artaserse_, and three on _Arminio_. The excellence of these opera-books in a dramatic point of view is sufficiently shown by the fact that many of them, including Metastasio's _Didone_, _Issipile_ and _Artaserse_ have been translated into French, and played with success as tragedies. The _Clemenza di Tito_, by the same author (which in a modified form became the _libretto_ of Mozart's last opera) was translated into Russian and performed at the Moscow Theatre during the reign of the Empress Elizabeth. In the present day, several of Scribe's best comic operas have been converted into comic dramas for the English stage, while others by the same author have been made the groundwork of Italian _libretti_. Thus _Le Philtre_ and _La Somnambule_ are the originals of Donizetti's _Elisir d'amore_ and Bellini's _Sonnambula_. Several of Victor Hugo's admirably constructed dramas have also been laid under contribution by the Italian librettists of the present day. Donizetti's _Lucrezia_ is founded on _Lucrèce Borgia_; Verdi's _Ernani_ on _Hernani_, his _Rigoletto_ on _Le Roi s'amuse_. [Sidenote: LIBRETTI.]