Oberon, Weber's song of the swan, has occupied my evening.--The execution of both the instrumental and vocal parts left much to desire; but on the whole, the opera was extremely well performed, for London. The best part was the decorations, especially at the conjuration of the spirits. They appear, not, as usual, in the standing costume,--scarlet jackets and breeches, with snaky locks and flames on their heads,--but in the form of huge rocky caves, which occupy the whole stage; every mass of rock then suddenly changes into some fantastic and frightful form or face, gleaming with many-coloured flames and lurid light, out of which here and there a whole figure leans grinning forward, while the fearful thrilling music re-echoes on every side from the moving chorus of rocks. The opera itself I regard as one of Weber's feebler productions. There are beautiful parts, especially the introduction, which is truly elf-like. I am less delighted with the overture, though so highly extolled by connoisseurs. I ought to have begun by telling you that I was presented to the King to-day, at a great levée.--I give you as a proof of the extraordinary voluntary seclusion of the present sovereign, that our Secretary of Legation was presented with me _for the first time_, though he has been here in that capacity for two years. His Majesty has a very good memory. He immediately recollected my former visit to England, though he mistook the date of it by several years. I took occasion to make my compliments to him on the extraordinary embellishment of London since that time, which indeed is to be ascribed in great measure to him. After a gracious reply, I passed on, and placed myself in a convenient station for seeing the whole spectacle. It was odd enough.