The other treatises of Hero are:—1. On the construction of slings. 2. On the construction of missiles. 3. On automata. These are published in Greek and Latin in the _Vet. Math._ 4. On the method of lifting heavy bodies. This treatise has not yet been edited: it exists only in an Arabic translation. 5. On the “dioptra” or spying-tube: also inedited. It exists in manuscript in the Royal Library at Vienna, and among the MSS. of Hero contained in the Library of the University of Strasburgh. Schweighæuser in his notice of these MSS. (ap. Fabric. iv. p. 226), intimates that this treatise is of much interest, and contains an account of the dioptra “newly invented or improved by Hero himself.” Some help might perhaps be derived from it towards the settlement of Hero’s date, as the dioptra is mentioned and minutely commented on by Polybius. Several other treatises, entirely lost, are enumerated by Fabricius, iv. p. 236. A question of great interest presents itself as to the claim of Hero to be considered as the inventor of the several machines and methods described by him. In the introduction of the “Pneumatica” he declares that his purpose is to arrange in order the discoveries of his predecessors, and to add to them his own. The treatise on the construction of missiles is ascribed in some MSS. to Ctesibius, (as in one at Leyden, Fabric. iv. p. 229,) while at the end of a MS. of the same work in the Library of Vienna are these words, τέλος τῶν Ἀρχιμήδους Βελοποιΐκῶν, τῶν ἐξηγηθέντων παρὰ Ἥρωνος Κτησιβίου. Again, it is singular that neither Pliny nor Vitruvius has any reference to Hero, though Ctesibius and his inventions are repeatedly mentioned. Vitruvius (x. 7) minutely describes a machine for raising water to a great height, which he expressly ascribes to Ctesibius; and in the following chapter he treats, at great length, of the construction of water-organs, yet without any notice of Hero. Both Pliny and Vitruvius expressly name Ctesibius as famous for his skill in the invention of pneumatic and hydraulic instruments. Pliny’s words are (vii. 38) “Laudatus est Ctesibius pneumatica ratione et hydraulicis organis repertis.” Vitruvius, (x. 7, compare also ix. 8,) after his description of the machine for raising water, says “Nec tamen hæc sola ratio Ctesibii fertur exquisita, sed etiam plures et variis generibus ab eo liquore pressionibus coacto spiritus efferre ab natura mutuatos effectus ostenduntur, uti merularum aquæ motu voces, atque engibata, quæ bibentia tandem movent sigilla, cæteraque quæ delectationibus oculorum et aurium usu sensus eblandiuntur.” He refers the curious to the commentaries of Ctesibius himself. How well this description of Ctesibius’ inventions suits the general character of those preserved by Hero, will be manifest at once. Vitruvius, as Schneider has pointed out,[3] seems to have had no knowledge of Hero’s Pneumatics, as both the forcing-pump and the water-organ differ in several important