A rare offprint which details an interesting scientific controversy. James Watt is largely perceived today as a steam engineer, but in this extensive and thorough critique he is given priority as the discoverer of ‘the true nature and composition of water’, over Henry Cavendish. While Cavendish clearly conducted his experiments first and is generally attributed with the accolade it was indeed Watt who first suggested that water was a combination of gasses, rather than an element in its own right. Lord Francis Jeffrey (1773 - 1850) was a Scottish judge and literary critic who edited the Edinburgh Review for over forty years, and though not credited as the author in this offprint, the article is highlighted by his biographer as being very last of his many contributions to the magazine (Cockburn, The Life of Lord Jeffrey with a Selection from his Correspondence, Edinburgh, 1852, Vol I, pp 402-403). Lord Jeffrey appears in a list of correspondents with Sir John Herschel and this may have been a presentation copy, but it is hard to establish whether or not the signature is in Herschel’s hand as known examples of his handwriting and signature display bewildering differences from one letter to another.