Another work was a commentary on Euclid (referred to by the Arabs as "the book of the resolution of doubts in Euclid") from which quotations have survived in an-Nairizi's commentary. The _Pneumatica_, _Automatopoietica_, _Belopoiica_ and _Cheiroballistra_ of Hero were published in Greek and Latin in Thevenot's _Veterum mathematicorum opera graece et latine pleraque nunc primum edita_ (Paris, 1693); the first important critical researches on Hero were G. B. Venturi's _Commentari sopra la storia e la teoria dell'ottica_ (Bologna, 1814) and H. Martin's "Recherches sur la vie et les ouvrages d'Heron d'Alexandrie disciple de Ctesibius et sur tous les ouvrages mathematiques grecs conserves ou perdus, publies ou inedits, qui ont ete attribues a un auteur nomme Heron" (_Mem. presentes a l'Academie des Inscriptions et Belles-Lettres_, i. serie, iv., 1854). The geometrical works (except of course the _Metrica_) were edited (Greek only) by F. Hultsch (_Heronis Alexandrini geometricorum et stereometricorum reliquiae_, 1864), the _Dioptra_ by Vincent (_Extraits des manuscrits relatifs a la geometrie pratique des Grecs, Notices et extraits des manuscrits de la Bibliotheque Imperiale_, xix. 2, 1858), the treatises on _Engines of War_ by C. Wescher (_Poliorcetique des Grecs_, Paris, 1867). The _Mechanics_ was first published by Carra de Vaux in the _Journal asiatique_ (ix. serie, ii., 1893). In 1899 began the publication in Teubner's series of _Heronis Alexandrini opera quae supersunt omnia_. Vol. i. and Supplement (by W. Schmidt) contains the _Pneumatica_ and _Automata_, the fragment on _Water Clocks_, the _De ingeniis spiritualibus_ of Philon of Byzantium and extracts on Pneumatics by Vitruvius. Vol. ii. pt. i., by L. Nix and W. Schmidt, contains the _Mechanics_ in Arabic, Greek fragments of the same, the _Catoptrica_ in Latin with appendices of extracts from Olympiodorus, Vitruvius, Pliny, &c. Vol. iii. (by Hermann Schone) contains the _Metrica_ (in three books) and the _Dioptra_. A German translation is added throughout. The approximation to square roots in Hero has been the subject of papers too numerous to mention. But reference should be made to the exhaustive studies on Hero's arithmetic by Paul Tannery, "L'Arithmetique des Grecs dans Heron d'Alexandrie" (_Mem. de la Soc. des sciences phys. et math. de Bordeaux_, ii. serie, iv., 1882), "La Stereometrie d'Heron d'Alexandrie" and "Etudes Heroniennes" (_ibid._ v., 1883), "Questions Heroniennes" (_Bulletin des sciences math._, ii. serie, viii., 1884), "Un Fragment des Metriques d'Heron" (_Zeitschrift fur Math. und Physik_, xxxix., 1894; _Bulletin des sciences math._, ii. serie, xviii., 1894). A good account of Hero's works will be found in M. Cantor's _Geschichte der Mathematik_, i.^2 (1894), chapters 18 and 19, and in G. Loria's studies, _Le Scienze esatte nell' antica Grecia_, especially libro iii. (Modena, 1900), pp.