Letter from Lighting Trades Limited, Oriel House, 30-31 Farringdon [Street], London, E. C. 4., to Professor [Alan Archibald Campbell] Swinton, 40 Chester Square, S. W. 1. Acknowledges receipt of Swinton's favour and in reply infomrs that the percentage of thorium and cerium contect to give the best efficiency are still substantially the same as those dealt with in Swinton's paper before the Royal Society. 25 November 1929