478 



reille: anti-aircraft firing 



The observer A, after having trained the aperture in such a 

 way that the machine aimed at appears as if following the wire, 

 registers the time taken by the machine to cross the aperture 

 from one side to another. 



This time gives the measure of the horizontal linear velocity 

 and the bearing of the plane of the aperture indicates the actual 

 direction of the flying machine. 





Fig. 8. 



(3) The extrapolation or prediction results from the knowl- 

 edge both of this actual direction and of the hnear velocity. 



As has already been said, this extrapolation gives the azi- 

 muth of the point to be aimed at; and, in this azimuth, the 

 angle of sight (fig. 8). 



The altitude of the point to be aimed at in the extrapolated 

 azimuth is supposed to be equal to the last altitude that has been 

 measured. The angle of sight results from the knowledge of the 

 altitude and of the abscissa; the latter is given by the intersec- 

 tion of the azimuth with the extrapolated horizontal direction. 



