302 ANNUAL REPORT 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 afew 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. 
