Euclid wrote other books on both elementary and higher geometry, and on the other mathematical subjects known in his day. The elementary geometrical works include the _Data_ and _On Divisions_ (_of figures_), the first of which survives in Greek and the second in Arabic only; also the _Pseudaria_, now lost, which was a sort of guide to fallacies in geometrical reasoning. The treatises on higher geometry are all lost; they include (1) the _Conics_ in four Books, which covered almost the same ground as the first three Books of Apollonius's _Conics_, although no doubt, for Euclid, the conics were still, as with his predecessors, sections of a right-angled, an obtuse-angled, and an acute-angled cone respectively made by a plane perpendiular to a generator in each case; (2) the _Porisms_ in three Books, the importance and difficulty of which can be inferred from Pappus's account of it and the lemmas which he gives for use with it; (3) the _Surface-Loci_, to which again Pappus furnishes lemmas; one of these implies that Euclid assumed as known the focus-directrix property of the three conics, which is absent from Apollonius's _Conics_. In applied mathematics Euclid wrote (1) the _Phaenomena_, a work on spherical astronomy in which ὁ ὁριζων {ho horizôn} (without κυκλος {kyklos} or any qualifying words) appears for the first time in the sense of _horizon_; (2) the _Optics_, a kind of elementary treatise on perspective: these two treatises are extant in Greek; (3) a work on the Elements of Music. The _Sectio Canonis_, which has come down under the name of Euclid, can, however, hardly be his in its present form. In the period between Euclid and Archimedes comes Aristarchus of Samos (about 310-230 B. C.), famous for having anticipated Copernicus. Accepting Heraclides's view that the earth rotates about its own axis, Aristarchus went further and put forward the hypothesis that the sun itself is at rest, and that the earth, as well as Mercury, Venus, and the other planets, revolve in circles about the sun. We have this on the unquestionable authority of Archimedes, who was only some twenty-five years later, and who must have seen the book containing the hypothesis in question. We are told too that Cleanthes the Stoic thought that Aristarchus ought to be indicted on the charge of impiety for setting the Hearth of the Universe in motion.