The fire-signals of the Greeks and Romans are also slightly mentioned by Quintus Curtius, Livy, Cæsar, Herodotus, Homer, and Thucydides; likewise by Vegetius and Frontinus; but still more in detail by Polybius and Æneas Tacticus; the latter of whom was contemporary with Aristotle, and has left a valuable fragment on the duties of a general, (translated into Latin by Casaubon,) wherein are many curious remarks on the subject of secret correspondence. The Greek signals were much improved by Polybius, who, in his history, (lib. x. cap. 45. p. 296. tom. iii. Lips. 1790. edit. Joh. Schweighaeuser,) attributes the invention to Cleomenes and Democritus, or (more correctly) to Cleoxenus and Democlitus, in words thus rendered: "Postrema ratio, cujus auctores sunt Cleoxenus et Democlitus, sed quam nos correximus, certa definitaque est, adeo ut quidquid exortum fuerit negotii, id possis certo facere notum." Prior to that period, the information communicated by torches, flags, smoke, or otherwise, was very limited, and it was requisite to settle beforehand what each signal should mean; whereas Polybius showed how to correspond alphabetically, and to give or receive any species of intelligence, without this previous concert. The plans of Æneas Tacticus had never arrived at such perfection, and were therefore of comparatively small use; though, without doubt, he at least equalled any of his predecessors in the facility of his telegraphic communications. No. VIII. A way how to level and shoot cannon by night as well as by day, and as directly, without a platform or measures taken by day, yet by a plain and infallible rule. No. IX. An engine, portable in one's pocket, which may be carried and fastened on the inside of the greatest ship, _tanquam aliud agens_, and, at any appointed minute, though a week after, either of day or night, it shall irrecoverably sink that ship. NOTE. To prepare this dangerous instrument, it is merely necessary to connect a gun-lock with a common bomb shell, filled in the usual manner, and a small clock attached; which will at any given time discharge the lock, and cause the shell to explode: the tremendous effects of which in the cabin or hold of a vessel may easier be conceived than described. No. X. A way, from a mile off, to dive and fasten a like engine to any ship, so as it may punctually work the same effect, either for time or execution. NOTE.