For anyone who ever wondered, the Periscopic Prism Co.'s premises were at 23 Prince of Wales Crescent, Kentish Town in London, now completely vanished.
Prince of Wales Crescent formed one side of a triangular island piece of land, bounded on the other sides by Prince of Wales Road and Malden Crescent, it intersected with P. of W. Rd at what is now the junction with Harmood Street. No.23 was on the S-E side and by the 1950s the site was occupied by a dairy. By the 1970s this area was very run down and Camden Council decided to demolish and redevelop it, obliterating the street pattern in doing so.
Some pictures of the street as demolition commenced are at Wednesday Picture: squats, creativity and destruction in 1970s West Kentish Town | Kentishtowner
For anyone who wants to see a scanned map at the National Library of Scotland, the grid square is TQ2884NW