INTERNATIONAL ATR MAP AND AERONAUTICAL MARKS. 
By Cu. LALLEMAND,? 
President of the French Association for the Advancement of Sciences. 
1. PRELIMINARY ACCOUNT. 
The dirigible air balloon, and more especially the aeroplane, which 
are scarcely out of the period of research and experiment, will soon 
enter into the area of practical politics. To-day, still mere instru- 
ments of sport or of military reconnaissances, they will become, 
to-morrow, valuable means of transport. It is time that aviators 
were given means for finding their way, similar to those which, for 
a long time, have existed for navigation and travel. 
Whether on sea, land, or in the air, the pilot has always before 
him the same triple problem to be solved. He must from time to 
time— 
1. Recognize his position. 
2. Determine the direction of the point to be reached. 
3. Rapidly estimate the distance remaining to be covered. 
For terrestrial locomotion, the solving of these various problems 
was greatly simplified by producing special maps for the use of trav- 
elers and by erecting along the principal routes easily visible signs, 
such as milestones, plates indicating the names and distances of more 
or less remote towns, signposts at road junctions, ete. But the mark- 
ing or buoying of routes presupposes a course fixed in direction 
and limited in extent. Admirably suited for travel by land, this 
system is still, to a certain extent, applicable to coasting trade, that 
is, for sea voyages along coasts or in estuaries. But, on the other 
hand, for travel on the high sea this method is unsuitable, and for 
aerial navigation quite useless in foggy weather or at night. In the 
latter case it is necessary to use acompass. In spite of fog, darkness, 
or the absence of marks, the use of the compass enables the pilot to 
follow the desired direction, which direction has been previously 
1 British Association, Portsmouth, September, 1911. Reprinted by permission from The Geographical 
Journal, London, vol. 38, No. 5, November, 1911. 
2 Inspecteur-Général des Mines, Directeur du Service du Nivellement général de la France, Membre de 
l'Institut et du Bureau des Longitudes. 
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