The account of the Chemistry of the Arabians is almost entirely limited to the works of Geber, which I consider to be the first book on Chemistry that ever was published, and to constitute, in every point of view, an exceedingly curious performance. I was much struck with the vast number of facts with which he was acquainted, and which have generally been supposed to have been discovered long after his time. I have, therefore, been at some pains in endeavouring to convey a notion of Geber’s opinions to the readers of this history; but am not sure that I have succeeded. I have generally given his own words, as literally as possible, and, wherever it would answer the purpose, have employed the English translation of 1678. Paracelsus gave origin to so great a revolution in medicine and the sciences connected with it, that it would have been unpardonable not to have attempted to lay his opinions and views before the reader; but, after perusing several of his most important treatises, I found it almost impossible to form accurate notions on the subject. I have, therefore, endeavoured to make use of his own words as much as possible, that the want of consistency and the mysticism of his opinions may fall upon his own head. Should the reader find any difficulty in understanding the philosophy of Paracelsus, he will be in no worse a situation than every one has been who has attempted to delineate the principles of this prince of quacks and impostors. Van Helmont’s merits were of a much higher kind, and I have endeavoured to do him justice; though his weaknesses are so visible that it requires much candour and patience to discriminate accurately between his excellencies and his foibles. * * * * * The history of Iatro-chemistry forms a branch of our subject scarcely less extraordinary than Alchymy itself. It might have been extended to a much greater length than I have done. The reason why I did not enter into longer details was, that I thought the subject more intimately connected with the history of medicine than of chemistry: it undoubtedly contributed to the improvement of chemistry; not, however, by the opinions or the physiology of the iatro-chemists, but by inducing their contemporaries and successors to apply themselves to the discovery of chemical medicines. * * * * *