INTERNATIONAL AIE MAP — LALLEMAND. 297 



direction to be followed is 26° to 27° W. of the meridian to the south, 

 say, magnetic S. 40° W. (the magnetic declination at Bourges being 

 13.5° W.). The compass should therefore show the complement, 

 say, N. 140° W. 



If necessary, this diagram could even suffice for traveling. A 

 straight line having been drawn joining starting point and destina- 

 tion,, the pilot can see that his way will run successively right across 

 the upper left angle of sheet 62, then cross the lower half of sheet 61, 

 thereafter cut the upper edge of sheet 51 about the center, pass 

 through the right-hand corner of the lower half of sheet 50, cut diago- 

 nally across sheet 40, graze the upper left corner of sheet 30, and 

 finally end about the middle of the lower half of sheet 39. 



Let us suppose that at any moment the pilot observes on the ground 

 below a mark similar to that of figure 2, with the two figures 5 and 

 on either side, respectively, and with a large dot occupying the proper 

 position of the town of Angouleme in the upper part of sheet 50 of 

 the index map. He would at once conclude that he had deviated 

 to the right of his route, and after a rough estimation he would incline 

 25° to 30° to the left. But, in every case, a detailed map would be 

 necessary for landing. 



Having examined many systems, the permanent committee for 

 aerial navigation of the public works department of the French Gov- 

 ernment recently proposed for this map and for aeronautical signs 

 the following solutions that seem to be the simplest ones and also 

 the most likely to be adopted by other countries: 



2. AIR MAP. 



In order to attain the required object and to keep to the necessary 

 clearness, an air map must show only the details required by airmen, 

 either for finding their way or for landing. 



To the first category belong the characteristic geographical features 

 of the terrain, such as railways, main roads, channels, streams and 

 rivers, lakes, forests, bushes, clumps of isolated trees, large areas of a 

 similar cultivation, large boroughs with their outline and principal 

 streets, chimneys of factories, clock towers, high towers, and, briefly, 

 all objects liable to attract the attention of the pilot from a distance, 

 either by means of their shape, dimensions, color, or situation. 



To the second category belong turf pits, thick hedges, irrigation or 

 drainage canals, electrical power lines traversing fields, and generally 

 all objects liable to impede landing; and, in addition, gasometers, 

 aerodromes and sheds where, if necessary, refuge or help could be 

 obtained. 



In the opinion of all competent authorities, the scale of 1 to 

 200,000 seems to be the most convenient one. On a smaller scale 

 the map would be less clear; on a larger scale unwieldy without 



