Copy letter from Robert William Frederick Harrison, to William Williams, 37 Alexandra Road, Blackburn In reference to Williamson's letter of the 28th, the papers Williams refers to on carbon dioxide in the Berlin Berichte and Paris Comptes Rendus are as under; W C Williamson 'Die Menge der in der Atmosphäre vorhandenen Kohlensäure' 1897, and M Henriet, 'Dosage rapide de l'acide carbonique dans l'air et les milieux confinés', 1896. Both these may be purchased from Messrs Dulau & Company, 37 Soho Square, W. 30 September 1899