TOPOGRAPHICAL SURVEYS 105 



with a graduated circle and a movable sighting arm (or alidade) 

 attached. The text explains how with this instrument it is 

 possible to determine the mutual relation of towns, i.e. by 

 observing the bearings of one from the other. For this it would 

 be necessary to orientate the instrument correctly at each 

 point, and Waldseemiiller explained, some years later, in the 

 booklet accompanying his * Carta itineraria', how this could be 

 done with a 'compass clock', that is, a combination of a sun 

 dial and compass. In the 1512 edition of the 'Margarita philo- 

 sophica' the instrument has become more elaborate; called a 

 'polymetrum', it consists in essence of the geometrical square 

 and alidade with a quadrant erected upon it, so that vertical 

 and horizontal angles could be observed. Some have seen in 

 this the prototype of the theodolite. 



The famous cosmographer and cartographer, Sebastian 

 Miinster, while at Heidelberg University, became acquainted 

 with the 'Margarita philosophica' and its rudimentary survey 

 instructions. In 1528, he published an appeal to his fellow 

 scholars to co-operate with him in a geographical description of 

 Germany, which he proposed to supplement with an atlas. 



"It is known and apparent that the regional maps of 

 Germany, as they have been issued in recent years, are not 

 constructed with correct observation of the azimuth, as is 

 well seen with the great bend of the Rhine between Stras- 

 burg and Mainz which in truth is not set down as I have 

 many times observed it." 



He suggested that each of his friends should undertake to 

 map the country within a radius of six to eight miles of their 

 town, and he described how this could be done. With the 

 instrument, in this case a quadrant divided in seventy-two 

 sections and oriented by a compass, the observer took the 

 bearing of a neighbouring village, drew a corresponding ray 

 upon a sheet of paper and marked off on it to scale the distance 

 between the two places. This operation was to be repeated at 

 each village or observation post. Miinster did not apparently 

 contemplate fixing positions by intersecting rays or calculating 

 distances from the triangles, without direct measurement. He 



