12. Many have testified to the amount of knowledge which this subject requires, and Hipparchus, in his Strictures on Eratosthenes, well observes, “that no one can become really proficient in geography, either as a private individual or as a professor, without an acquaintance with astronomy, and a knowledge of eclipses. For instance, no one could tell whether Alexandria in Egypt were north or south of Babylon, nor yet the intervening distance, without observing the latitudes.[43] Again, the only means we possess of becoming acquainted with the longitudes of different places is afforded by the eclipses of the sun and moon.” Such are the very words of Hipparchus. 13. Every one who undertakes to give an accurate description of a place, should be particular to add its astronomical and geometrical relations, explaining carefully its extent, distance, degrees of latitude, and “climate.”[44] Even a builder before constructing a house, or an architect before laying out a city, would take these things into consideration; much more should he who examines the whole earth: for such things in a peculiar manner belong to him. In small distances a little deviation north or south does not signify, but when it is the whole circle of the earth, the north extends to the furthest confines of Scythia,[45] or Keltica,[46] and the south to the extremities of Ethiopia: there is a wide difference here. The case is the same should we inhabit India or Spain, one in the east, the other far west, and, as we are aware, the antipodes[47] to each other. 14. The [motions] of the sun and stars, and the centripetal force meet us on the very threshold of such subjects, and compel us to the study of astronomy, and the observation of such phenomena as each of us may notice; in which too, very considerable differences appear, according to the various points of observation. How could any one undertake to write accurately and with propriety on the differences of the various parts of the earth, who was ignorant of these matters? and although, if the undertaking were of a popular character, it might not be advisable to enter thoroughly into detail, still we should endeavour to include every thing which could be comprehended by the general reader.