476 



REILLE : ANTI-AIRCRAFT ' FIRING 



Among these methods the one to be pointed out in particu- 

 lar is the direct method which consists in the following: 



The observer B announces simply by telephonic signal the 

 successive passages of the flying machine in the azimuths 1, 2. 

 3 — determined in advance, for example every ten degrees, 

 starting from the true south. 



The observer A moves on a plotting-board a vertical rule 

 along the azimuth for which the first signal is expected and 

 this in such a way as to sight the flying machine on the edge 

 of this rule. 



At the moment of the telephonic signal the altitude h of the 

 machine is given by simply reading the height at which it ap- 



Fig. 6. 



pears on the rule; and its horizontal projection is given by the 

 position of the lower end of the rule (fig. 6). The board is sup- 

 posed to be duly oriented and scaled; the rule to be accordingly 

 scaled. 



Remarks, (a) This direct method permits the continuous 

 tracing of the flight of the machine, once its altitude is known. 

 If, in fact, after the signal, the observer A keeps on moving 

 his vertical rule no longer along the azimuth but in such a way 

 that the flying machine is maintained sighted at the same alti- 

 tude h on the edge of the rule, the lower end of the rule will auto- 

 matically trace on the board the projection of the flight of the 

 machine (taking for granted, of course, that the machine does 

 not change its altitude). 



