This is an advertisement for a trapeze and acrobatics duo, Kairo and Olga, whose exploits in 'flying' were most likely simulated by the use of strong wires invisible to an audience.
The Canterbury Theatre was one of the earliest music halls in London, opened in 1850 and run by Charles Morton – the self-styled 'first great entrepreneur' of the form. Music hall was an inexpensive and relatively respectable form of popular variety entertainment; not as formal or socially exclusive as opera or mainstream theatre, but not as seedy or bawdy as the pop-up variety shows of the East End. People of all ages attended, witnessing acrobatic acts like this one, as well as popular scenes and songs from operas, vernacular songs about contemporary urban life, and dancers. Music halls where also usually licensed premises were alcohol and tobacco were sold.