A glass harp
Molloy is annoyed at Edith's making musical notes from her filled water glass and refers to the glass harmonica. In fact, what he describes is really a glass harp, a predecessor of the glass harmonica invented by Richard Pockrich in the 1740s. Using wet fingers on the rims of glasses filled with different quantities of water to make musical notes was a technique known since the Renaissance.
A glass harmonica
Having seen one of these glass harps played in Cambridge (England) Benjamin Franklin invented, in 1761, a vertical arrangement of glass bowls rather than using the horizontally placed glasses and called it the glass armonica. Incidentally, this use of the word harmonica predates the mouth organ by some sixty years. Mozart, Beethoven and Saint-Saens (the Carnival of the Animals contains a part for glass harmonica) all wrote music for the glass harmonica. The instrument pretty much disappeared after the end of the eighteenth century, probably because it could not generate enough noise to be heard in large concert halls. There were also (unfounded) rumours that playing it made people go mad because of the plaintive sound the instrument made or that (equally unfounded) that the lead in the glass poisoned the players.
The Royal Academy's Hanging Committee
Edith Challenor's idea of having a committee to assess which inhabitants of London may parade naked on the streets is likened to the Hanging Committee of the Royal Academy. When it was established in 1768 one of its key objectives was to provide an annual exhibition and the first exhibition took place the following year. Any artist may submit works to be judged by the committee and today about 10% of those paintings submitted are accepted for display in the exhibition at the Academy in Piccadilly. Agent Triple P had a picture accepted some decades ago! The idea of an attractiveness committee was also suggested by the fact that three towns on the Italian Riviera, in 1993, banned fat women from wearing bikinis and enforced an arbitrary vital statistics measurement to ensure unpleasant figures didn't spoil the beaches!
Molloy worries about the cost of his hotel bill at the Great Northern but relaxes when he is given £100. A set menu lunch or dinner at a London hotel at the time would have been about three shillings (twenty shillings to the pound) a head. A room at a really top hotel like the Ritz would have been about £3 a night. A lesser domestic servant or an office clerk would have earned around £250-£350 a year. The five pound notes he is given had not changed in appearance very much since they were first issued in 1793 and continued in circulation until as late as 1961. These were very large notes; 212 mm in length and 134 mm in width (about nine by five inches).