WHILE the Editor of the present work was engaged in writing an Analytical History of the Steam-Engine, it became necessary to consult the antient mechanicians to ascertain who were the inventors of the several parts composing that machine: the earliest writer on the subject appeared to be Hero of Alexandria; throughout whose work so many of the elementary parts of all Steam-Engines, and those also of most other machines are mentioned, that it was thought a translation of Hero's Pneumatics would be acceptable not only to the Engineer but to the scientific world generally. Although at the commencement of his work, Hero states that he has added his own discoveries to those "handed down by former writers, yet in no instance has he pointed out any thing which originated with himself ; nor is there any statement in the text, except the one I have just quoted, which would lead the reader to any other conclusion than that the whole is a compilation from the works of those who at that period of time were styled the " antient philosophers and mechanicians." Those parts of each vessel or instrument which mechanincally perform the operations assigned to them are alike, or nearly so, in the four manuscript and the three printed copies of Hero's works which have been consulted by the Editor; but great diversity of form is given to the vessel in which they are placed. The drawings have been made expressly for this work from the best examples. The seventy-eighth proposition is the only instance in which there is an omission of the illustrative drawing, and this occurs in all the copies; the two drawings which are now supplied to that proposition have been made from the descriptions given in the text. For the Translation of hero from the Creek, the valuable assistance of Mr. J. G. Greenwood, Fellow of University College, London, has been obtained he is the recently appointed Professor of the Languages and Literature of Creece and Rome, in Owen's College, Manchester. It is confidently hoped that this Translation will be found superior to its predecessors in whatever language ; and that it will prove not only generally interesting but practically useful.Translator's Preface.