Pope's 'The New Bath Guide or, Useful Pocket-Companion; Necessary For all Persons residing at, or resorting to this antient [sic] and opulent City.' published in 1762tells us:
'There are two public Assembly-Rooms in this Place Mr. Simpson's, and Mr. Wiltshire's: The largest kept by Mr. Simpson; was built in the Year 1750 90 Feet in Length, 36 in Breadth, and 30 in Height; it has a very fine Stocco Ceiling; there is hung up in it a Portrait Picture of the late Richard Nash, Esq. Master of the Ceremonies, besides several very fine Landscapes, and is thought to be as elegant a room for its size as any in England.'
'Mr. Wiltshire's Room is 36 Feet in Length, 30 in Breadth, and 30 in Height; this has a Cove Ceiling, and is a very neat Room; it is likewise ornamented with a Portrait Picture and Bust of the Late Richard Nash, Esq. besides many curious Landscapes. - There are to each Room Antichambers, which are often used for performing Concerts in, and for Card-Rooms.'
By way of comparison, the ballroom of the Upper Rooms built a decade later is 30m x 12m, against Wiltshire's 27m x 9m and Simpson's 11m x 9m.
'The Balls (during the season) are twice a week, viz. Tuesday and Fridays; and the Company assemble at one of the Rooms every night. Mr Simpson's Nights are Tuesdays, and Saturday's; and Mr. Wiltshires are Mondays, Wednesday's, and Fridays; they have Sundays alternately.'
Wiltshire's Rooms were the Assembly Rooms on the Parades, the site is now known as Bog Island. They had been called Wiltshire since they had been taken into the ownership of the Wiltshire family in 1744. The Wiltshire's were a very wealthy and influential Bath family who made their money as carriers, transporting high-value goods between London and Bath and as bankers. In 1762 the Rooms were being run by John Wiltshire.