Meanwhile, it is with no small amount of diffidence and hesitation that the present Translation will quit my hands. Hemmed in by a rigid dialectic terminology upon all sides, I have had difficulties of no ordinary kind to contend with in adapting a language, composed of such varied elements as our own, to meet the requisites of general clearness and conciseness that form so prominent a feature of the German work. If errors and obscurities exist, the blame, it will be observed, attaches to myself, not to the distinguished author. Ill-health has conflicted much with the calmness and repose of mind so indispensable to an undertaking, at once novel in kind and character to the English reader; or otherwise, these (my last labours unto any extent as a Translator) might have been rendered more worthy of the Ray Society and the objects it has in view. To those who have kindly afforded me assistance in the progress of the work, and to the latter body for undertaking it, I here return many grateful thanks. The Author himself in a letter to the Translator, dated Jan. 12, 1847, acknowledges the acceptance of his work by the Society in the following words:--"The intelligence of my Physio-philosophy having been deemed worthy of translation by so goodly and enlightened a Society, cannot be otherwise unto me than a source of delight."[B] ALFRED TULK. [B] "Die Nachricht dass meine Naturphilosophie von einer sociferigen und erleuchteten Gesellschaft der Uebersetzung für würdig erachtet worden ist, konnte nicht anders als mir Freude gewähren." AUTHOR'S PREFACE TO THE TRANSLATION. It is with no readiness or pleasure that I write introductions of any kind, and usually abstain from doing so, partly because they appear to me like a kind of apology or makeshift for the author, and partly because the contents of the book itself should indicate his status or position. With regard, however, to the history of the work, some few words are certainly requisite for its Translation.