RSA - John Adam Street, London, UK - Blue Plaques on Waymarking.com

The plaque, that is set to the left of the main entrance door, tells us:

The
House of the
Royal Society for
the Encouragement
of Arts Manufacturers
and Commerce
Foundation laid 28 March 1772
Completed 24 April 1774
Robert & James Adam
Architects

The RSA building is Grade I listed with the entry at the English Heritage website telling us:

Learned Society premises and lecture hall. 1772-74 by Robert Adam. Brown brick with stone dressings, slate roof. Chaste Adam temple front. 3 main storeys, attic and basement. 3 widely spaced window bays. Central tripartite doorway of panelled door and side lights framed by pilasters and central projecting porch with "Tower of the Winds" columns and pilasters, fluted frieze with paterae and swags and cornice. Flanking recessed glazing bar sashes under flat gauged arches, but to the centre on 1st floor is a large Adam Venetian window inscribed in a semicircular arched recess with fan decoration to head above the 3 lights, the centre one arched, divided by slender Ionic columns. Above plat band the 3 bays of the upper floors are articulated by a giant engaged order of Ionic columns carrying entablature with triglyph frieze interrupted by inscription "Arts and Commerce Promoted", cornice and dentil pediment. Cast iron area railings with pineapple finials. The rear, exposed through to Strand, also has a monumental elevation with 4 stone fluted Ionic pilasters through blind 1st and 2nd floors, framing figure panels, with entablature and pediment. The interior retains a number of fine original features including the lower part of the staircase, the library with its column screen and chimneypiece and the lecture hall which although redecorated by J.R. Hay in 1846, retains James Barry's great sequence of wall paintings etc.