Letter from [Alan Archibald Campbell] Swinton, to Messrs. J. T. Robin, Ltd., Greyhound Lane, London, S. W. 16 Referring to a paper he read at the Royal Society where he asserted that a gas flame burning with a mantle gives the best efficiency if the mantle were composed of 99% of thorium oxide and 1% of cerium oxide. Wishes to confirm whether this is still the case. 23 November 1929