A general map of the moon is shown in Plate VI. It has been based upon drawings made with small telescopes, and it gives an entire view of that side of our satellite which is presented towards us. The moon is shown as it appears in an astronomical telescope, which inverts everything, so that the south is at the top and the north at the bottom (to show objects upright a telescope requires an additional pair of lenses in the eye-piece, and as this diminishes the amount of light reaching the eye they are dispensed with in astronomical telescopes). We can see on the map some of the characteristic features of lunar scenery. Those dark regions so conspicuous in the ordinary full moon are easily recognised on the map. They were thought to be seas by astronomers before the days of telescopes, and indeed the name "Mare" is still retained, though it is obvious that they contain no water at present. The map also shows certain ridges or elevated portions, and when we apply measurement to these objects we learn that they must be mighty mountain ranges. But the most striking features on the moon are those ring-like objects which are scattered over the surface in profusion. These are known as the lunar craters. To facilitate reference to the chief points of interest we have arranged an index map (Fig. 27) which will give a clue to the names of the several objects depicted upon the plate. The so-called seas are represented by capital letters; so that A is the Mare Crisium, and H the Oceanus Procellarum. The ranges of mountains are indicated by small letters; thus a on the index is the site of the so-called Caucasus mountains, and similarly the Apennines are denoted by _c_. The numerous craters are distinguished by numbers; for example, the feature on the map corresponding to 20 on the index is the crater designated Ptolemy. A. Mare Crisium. B. Mare Foecunditatis. C. Mare Tranquillitatis. D. Mare Serenitatis. E. Mare Imbrium. F. Sinus Iridum. G. Mare Vaporum. H. Oceanus Procellarum. I. Mare Humorum. J. Mare Nubium. K. Mare Nectaris. _a._ Caucasus. _b._ Alps. _c._ Apennines. _d._ Carpathians. _f._ Cordilleras & D'Alembert mountains. _g._ Rook mountains. _h._ Doerfel mountains. _i._ Leibnitz mountains. 1. Posidonius. 2. Linne. 3. Aristotle. 4. Great Valley of the Alps. 5. Aristillus. 6. Autolycus. 7. Archimedes. 8. Plato. 9. Eratosthenes. 10. Copernicus. 11. Kepler. 12. Aristarchus. 13. Grimaldi. 14. Gassendi. 15. Schickard. 16. Wargentin. 17. Clavius. 18. Tycho. 19. Alphonsus. 20. Ptolemy. 21. Catharina. 22. Cyrillus. 23. Theophilus. 24. Petavius. 25. Hyginus. 26. Triesnecker.