According to NG2:
A form of musical notation and the system of teaching sight-singing which depends upon it, both devised by John Curwen in mid-19th-century England. One of the few alternative forms of notation to achieve international use in modern times, Tonic Sol-fa had its origin in Guidonian solmization, depending like that system upon aural perception of relative pitch (see Solmization, §I), but incorporating many features adopted empirically from other sources. First designed as an aid to beginners, Tonic Sol-fa was mistakenly regarded by its extreme exponents late in the 19th century as superior to standard notation in its own right. Consequently distrusted and misunderstood by many professional musicians, the system passed through a more recent period of disfavour and neglect. It is now seen to offer distinct advantages when employed purely as an ancillary device in the early stages of learning to read from notes; and, particularly following its adoption in modified form by Zoltán Kodály for use in Hungarian schools, it is employed for that purpose today in many parts of the world (see Schools).
There is a lengthy article that follows the above introduction.
If you go to
http://hdl.handle.net/1802/14369 you can see an example of the notation.