We first thought Francis Bacon but he normally has more hair, and, so far, all the heads are literary rather than scientific.
Site: Old Westminster Library - 6 heads (7 memorials)
SW1, Great Smith Street
The foundation stone is immediately to the right of the central entrance.
Above the entrance: "Westminster Public Library, The united parishes of St Margaret and St John the Evangelist, AD 1893". In 1985 this building was threatened with demolition and was only saved by a campaign which brought about the Thorney Island Society.
The Listing identifies the heads for us, and we've numbered them left to right.