reille: anti-aircraft firing 469 



If we draw on a vertical plane (fig. 1) the locus of all points 

 of burst obtained on the various trajectories by a given fuse 

 setting, we shall then have a curve. This curve will be the 

 locus of the points which the projectile reaches within a given 

 time (time of fuse) if the fuse is a clock-fuse. For that reason 

 it would be proper to call the curve an isochrone curve. 



Now let us turn around through all the azimuths a vertical 

 plane on which has been drawn the diagram showing: 



(1) The sheaf of the trajectories from degree to degree of 

 angle of departure. 



(2) The sheaf of the isochrone curves from second to second 

 of the time of flight (this supposed to be equal to the time of 

 fuse). 



Thus, each trajectory will generate a surface of revolution 

 determined by its angle of departure 0; we will call this sur- 

 face "the surface <J>" (see fig., 2). 



Each isochrone curve will generate a surface of revolution 

 determined by its time of flight d; we wHl call it 'Hhe surface 9." 



Any point in space will be determined by the intersection of 

 three surfaces (fig. 2): azimuthal plane, fi; trajectorial surface, 

 $, isochronic surface, 6; and will have, as an aerial target, 

 three balUstic coordinates: angle of azimuth, co; angle of de- 

 parture, 0; and time of flight (or of the fuse), d. 



Of these three ballistic coordinates of the point, the azi- 

 muth only is at the same time a geometric coordinate. 



As the geometric coordinates are the only ones that can 

 be obtained by direct measurement, in particular by sighting, 

 the balUstic coordinates and 6 have to be obtained indirectly, 

 by the following means, for instance: 



The target will be located in the azimuthal diagram bj^ the 

 measurements of its altitude and of its angle of sight (apparent 

 elevation a) and, once it is thus located in the plane of the dia- 

 gram, a simple reading will tell on which trajectory and on 

 which isochrone it is. 



Ill 



In the preceding paragraphs we have taken for granted that 

 the time at the end of which the shell burst is equal, whatever 



