no means inconsistent with the statement of Aristocles, since it is not necessary, with Clinton, to assign the whole of the long reign of Euergetes II. to Ctesibius, and then to put Hero so low down as the reign of Ptolemy VIII. The treatise on Pneumatics was first published in an Italian translation by Aleotti (Bologna, 1547). In 1575 appeared a Latin version by F. Commandine (Urbino, 1575): this translation, through which the work has been most extensively known, was reprinted at Amsterdam and at Paris. Several other translations were made into Italian, and one into German (see Fabricius, iv. p. 235). It was not till the year 1693, and subsequently to the appearance of all the versions named above, that the Greek text was published at Paris in the _Veterum Mathematicorum Opera_. The design of this collection was formed by Thevenot, deputy librarian of the Royal library in the reign of Louis XIV., and after his death it was carried out by De la Hire. Thevenot’s plan was to publish an accurate transcript of the MSS. of the several authors. The inevitable obscurity arising from the numerous corruptions which had crept into the manuscripts was to be remedied by an appendix of notes and a Latin translation. But for the Pneumatics of Hero it seemed sufficient to adopt the already well-known translation of Commandine; and, in consequence, of the eight MSS. of this treatise existing in the Royal Library, that one was chosen which most nearly agreed with the Latin version. This MS. was closely followed, and, as might be expected, the printed text is extremely corrupt: not unfrequently entire clauses are wanting, which, ending with the same word as the clause preceding, seem to have been passed over by the transcriber, whose eye, in returning from his copy to the original, rested on the second instead of the first of the two similar words. These defective passages, which appear to have been conjecturally restored by Commandine, have been supplied in the present translation from MSS. of Hero preserved in the British Museum. These MSS. are described in the appendix, where the most important cases in which the printed text has been supplemented, or otherwise amended, from this source are collected. When any words are included in the translation between brackets, it is to be understood that they appear neither in the text nor in any of the MSS. collated, but have been inserted as necessary to the sense.