302 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1911. 



an error of 10° of either longitude or latitude. In latitudes between 

 40° and 50° this error would amount to 1,100 kilometers (700 miles) 

 of latitude, or from 700-800 kilometers (400-500 miles) of longitude. 



In an area covering the whole of France, only the extreme points 

 of Brittany and the Vosges will have marks showing the same num- 

 bers. Consider, for instance, the marks numbered 39 in the environs 

 of Pau. The same number as this, on land, would not occur again 

 nearer than points in Algeria, England, Belgrade, or Hamburg, and 

 would not appear at all in Spain or Italy. To mistake such dissimilar 

 countries would be practically impossible. 



To determine the correct coordinates of a mark, an aviator would 

 only have to add to the number shown the hundreds and tens of 

 degrees of polar distance and longitude. The remainder, with an 

 error of perhaps a tenth of a degree (or a few minutes), could be esti- 

 mated by examining the position of the dot, with reference to the 

 sides of the mark. The position of the mark could thus be estimated 

 with an error of less than 10 kilometers (6 miles) in either direction. 



4. CONCLUSION. 



The initiative thus taken by France in producing an air map and 

 establishing aeronautical marks will very probably be followed by 

 other countries. In such a case it would be necessary to have an 

 international agreement to give definitely the conventional signs of 

 the air map and other details. 



In May last the cartographical committee- of the International 

 Aeronautical Federation, which met in Brussels to consider such 

 questions, adopted in principle the meridian of Greenwich as the 

 origin of the longitudes, a scale of 1 : 200,000 for the air map, and for 

 the limits of the sheets, meridians and parallels one degree apart, 

 starting from Greenwich and the Equator, and decided that electrical 

 power lines, which are so dangerous for airships and aeroplanes 

 when landing, should be shown on the map. 



As regards the aeronautical marks, this committee did not venture 

 to select any one system out of the numerous ones that were pro- 

 posed, and only suggested that the names of the respective localities 

 should be marked, in large letters, on roofs, especially on those of 

 railway stations. As many stations, however, would thus show the 

 same name, this would be a source of error and confusion; in addition 

 to this, the aviator would have to consult a dictionary of names of 

 boroughs, in order to find the number of the sheet of the air map which 

 he requires. A system of marks showing the cutting lines of the 

 sheet concerned, together with an abbreviated distinguishing number, 

 seems to be much more precise, significant, and certain. It is there- 

 fore to be hoped that sooner or later this system will be universally 

 adopted. 



