Geography (Geographicae Enarrationis Libri Octo)

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Through Sciotheroscopia observation of shadows to determine time/position, they observed the signs original: "signa d . o" which were over the vertex, the distances according to the circumference that was intercepted there under the meridians, which would be similar to the journey. And since these were established individually, as we have said, on a plane, the straight lines which went out through the extremities to the signs that were over the vertex met among themselves, because the center of the circles was the common point of coincidence. Therefore, as much as the circumference appeared that was between the vertical signs, and was a part of the circle which is inscribed through the poles, they supposed that much distance also existed on the earth of the whole circumference. Hence, if we have taken the distance not through the circle measured by the poles, but from any of the greatest circles, the proposition can be shown. The same will be clear to us if, through an instrument by which higher things are considered, the elevations of the pole have been observed in the termini, and also the position observed which the distance has to another meridian. Through which Meteoroscopium an astronomical instrument for observing stellar positions we can easily detect many other very useful things. But also, on any day and night according to the place of observation, the elevation of the Northern pole, and at every hour the meridional position, as well as the conditions of the declinations to it, that is, what angles the circle described by the way makes with the meridian, to the sign which is over the vertex, through which we similarly show the sought-after circumference from the Meteoroscopium itself, and also that which is intercepted between two meridians, when they were others than the equinoctial parallels. So that through such a method, if only one straight distance on the earth has been measured, the whole number of stadia units of distance which the circumference contains can also be found. Through these, from then on, the remainder and the intervals of other journeys are also known even without measurement, although they were not entirely straight, nor established under the same meridian or parallel, provided that which is proper to every inclination is diligently taken, and likewise the elevations of the termini are observed. Again, through the ratio of the circumference which extends the distance to the greatest circle, the multitude of stadia units of distance from the detected circumference of the whole earth can be easily considered.

THAT THOSE THINGS WHICH ARE OBSERVED FROM APPEARANCES OUGHT TO BE PREFERRED TO THOSE WHICH ARE DISCOVERED FROM THE HISTORY OF TRAVEL.

CHAPTER IV.

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THEREFORE, since these things are so, if those who traveled through the regions bit by bit had used such observations, they could have made a thoroughly certain description of the globe. But since Hipparchus Greek astronomer and mathematician alone has handed down to us the elevations of the Northern pole for a few cities (in respect to such a multitude as it is necessary to designate in Geography), and those subject to the same parallel; indeed, some with them likewise certain opposite places, not which were equally distant from the equinoctial, but which were clearly under the same meridian, from the fact that their mutual navigations tended to the north or to the south. But the distances which are the greatest, and especially those which tend to the east or west, have attained a more imperfect tradition, not by the carelessness of those who compiled the histories, but perhaps because the mathematical considerations had not yet been exactly perceived, nor had many lunar eclipses yet been observed at the same time in different places. For it has been committed to writing that the eclipse which happened at the fifth hour in Arbela an ancient city in Mesopotamia appeared in Carthage an ancient city in North Africa at the second. From which it is made manifest by how many equinoctial times places are distant from each other toward the east or west. It will also be reasonable and consequent to these that he who wishes to treat Cosmography the science of mapping the universe should presuppose those places which have been apprehended through more diligent observations as certain foundations for his designation, and adapt those which have been handed down by others to these, until their positions among themselves, with those which were previously observed as more certain than traditions, most especially agree.