The Ruwenzori Range. 
foremost, was that of his immediate precursor, Marinus of Tyre, or else those 
gathered by himself from the more or less accurate reports of travellers and 
seafarers. ( s ) All can see how defective such a method must be. 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 impossible 
to obtain 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 by Ptolemy with the 
stadium unit equivalent to the 500th part of the equatorial degree. ( 10 ) But 
we know that those routes were based on a different unit of measure, namely, 
the Olympic stadium of 600 to the equatorial degree. Hence, if for instance, 
it was a question of an itinerary of 3,000 stadia (in the direction of the 
meridian), the number of corresponding degrees would be 5° of latitude 
according to the Olympic measure, while according to Ptolemy it came to 6°. 
And in general, to obtain the true, or the approximately true, differences of 
latitudes and longitudes, we have to multiply by £ those given bv the 
Geographer, or, which is the same thing, reduce them by £. At the same time 
this single operation is very far from sufficing to introduce any accuracy into 
the Ptolemaic tables. 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 was 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 knowledge possessed by the ancients of many places and countries, 
from the inevitable 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 astounding, 
that the above-mentioned single reduction by £ suffices for the geographical 
sketch of the Upper Nile lands, such as is drawn by Ptolemy’s Geography, to 
correspond broadly if not precisely with that presented to us by the modern 
maps. On this no doubt quite casual coincidence it will not be useless to dwell 
for a moment. 
The latitude of Alexandria is given by Ptolemy as 30 30' N. (it is really 
31° 12'); from Alexandria to the parallel of the eastern lake are therefore 
reckoned 37° 30' E. = 37° E. Now the £ of 37 5' are equivalent to 31 c 25' = 
31° 15', and that lake thus falls under 0° 45' south latitude. A similar 
calculation for the western lake brings us to north latitude 0° 9'. ( n ) These 
U 2 
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