INTERNATIONAL AIR MAP AND AERONAUTICAL MARKS. 



By Ch. Lallemand, 2 

 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 airoad junctions, etc. 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 a compass. 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-General des Mines, Directeur du Service du Nivellement general de la France, Membre de 

 l'lnstitut et du Bureau des Longitudes. 



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