Solresol (also called langue musicale universale (Universal Musical Language) was invented by Jean Francois Sudre (1798-1866), a French music teacher, early in the 19th century. It is based on the eight-note musical scale. It could be spoken, sung or played on a musical instrument. At the beginning of the twentieth century there may still have been some speakers, making it one of the longest lived artificial languages. (Information from the Cambridge Encyclopaedia of Language)
Many people have contacted me about Solresol, and it seems that there may be enough people around to revive the language. Since no-one appears to have spoken it for nearly a century, this is going to be an interesting task! Fortunately, there is no challenge in trying to deduce what a "native accent" may have been, since musical notation has remained consistent, and it was adequate for writing SolReSol.
Currently, we know of two books that teach Solresol. I (and a lot of other people) am desperately trying to get hold of either of them, which we intend to put on the web. We only know translations for a small number of words - much of which was derived from information found in a lengthy quote from "The Artificial Language Movement" by Andrew Large.
There are quite a number of enthusiastic people who are attempting to resurrect SolReSol.