The Ruwenzori Jiange. 



foremost, was that of his immediate precursof, Marinus of Tyre, or else those 

 gathered hy himself from the more or less accurate reports of travellers and 

 seafarers. (**) All can see how defective such a method must l)e. From the 

 early itineraries traced without compass in determining the directions, without 

 chronometers for the intervals of time and distances, and without sufficient 

 knowledge of the marine and atmospheric currents, it was obviously impossi1)le 

 to ol)tain other than quite hypothetic, and for the most part only roughly 

 approximate results. (■') The reduction of the route distances to astronomic 

 notations (degrees and fractions of degrees) was made l>y Ptolemy with the 

 stadium unit equivalent to the 500th part of the equatorial degree. ('") But 

 we know that those routes were based on a different unit of measure, namely, 

 the Olympic stadium of GOO to the ec^uatorial degree. Hence, if for instance, 

 it was a question of an itinerary of .'?,000 stadia (in the direction of the 

 meridian), the number of corresponding degrees would l)e 5" of latitude 

 according to the Olympic measure, while according to Ptolemy it came to 6'. 

 And in general, to oi»tain the true, or the approximately true, diflerences of 

 latitudes and longitudes, we have to multiply by f those given by the 

 Geographer, or, which is the same thing, reduce them l)y ^. At the same time 

 this single operation is very far from sufficing to introduce any accuracy into 

 the Ptolemaic taldes. It cannot be asserted in the first place that all the 

 itineraries without exception were recorded in Olympic stadia ; nor is the 

 possibility to be excluded that for some of them the stadium of Eratosthenes 

 of 700 to the equatorial degree w^as taken as the unit ; in which case the 

 reduction should be by f . Moreover, in a great many cases there occur errors 

 of another nature, amongst which outstanding are those derived from the 

 imperfect knowdedge possessed by the ancients of many places and countries, 

 from the inevita])le inaccuracies in the calculation of distances and in 

 determining the relative positions, from the windings of the route followed and 

 so on. Despite of all this it is remarkable, not to say absolutely astovmding, 

 that the above-mentioned single reduction by } suffices for the geographical 

 sketch of the Upper Nile lands, such as is drawai by Ptolemy's Geography, to 

 correspond broadly if not precisely with that presented to us by the modern 

 maps. On this no doubt ([uite casual coincidence it will not he useless to dwell 

 for a moment. 



The latitude of Alexandria is given by Ptolemy as .30" 30' X. (it is really 

 31° 12'); from Alexandria to the parallel of the eastei-n lake are therefore 

 reckoned 37 30' E. = 37° E. Now the ^ of 37 5' are equivalent to 31' 25' = 

 31° 15', and that lake thus falls under 0" 45' south latitude. A similar 

 calculation foi- the western lake brings us to north latitude 0" 9'. ('^) These 



291 U 2 



