[...] If you would like to hear another piece of good news, it is that, although I have completed only the first act of “Siegfried” this winter (when I was frequently interrupted in my work, firstly by Liszt’s visit and later by a great feeling of exhaustion), it has turned out better than I could ever have expected. It was completely new ground for me, and, after the terrible tragedy of the “Valkyrie”, I entered upon it feeling fresher than I have ever done before: now that this act has turned out as it has done, I am convinced that Young “Siegfried” will be my most popular work, spreading quickly and successfully, and drawing all the other dramas after it, so that it is he who will most likely become the founder of a whole Nibelung dynasty. But it seems increasingly probable that the first performance of the whole thing will not take place before 1860; for even when I have completed the whole of the music, I shall still need a full 12 months for the preparations, although these should be made simpler for me by the fact that I have already come across a number of felicitously talented performers.
[...]
Source: Selected Letters of Richard Wagner, trans. and ed. Stewart Spencer and Barry Millington (W. W. Norton & Company, 1988), No. 198