eeille: anti-aircraft firing 473 



If the curve ab, in the vicinity of b, has no pronounced curva- 

 ture, the point c can be considered as located on the tangent to; 

 that curve drawn from point b in the direction of movement. 



The problem of extrapolation with respect to the flying ma- 

 chine (fig. 4) is, with one dimension added, a problem quite 

 similar to the ones commonly dealt with in firing at moving 

 targets at sea, and worked out by the coast artillery by means of 

 the plotting board: 



The positions Si, So, S3 of a ship are, by triangulation, regis- 

 tered on the plotting board at the times ti to, tz. The point 

 Si at which it is necessary to aim in order to reach the ship 

 at the time ^4 is given by a graphical extrapolation of the plotted 

 track Si, S2, Ss- 



The solutions which have been given to the same problem in 

 space with respect to anti-au-craf t firing are of two general kinds : 

 . (1) Solution by measurements of the angular velocity of the 

 target. 



(2) Solution by measurement of its Unear velocity. 



(1). The angular velocity of a flying machine with reference 

 to the eye of the observer (or with reference to the position of 

 the gun if observation is supposed to be made from this position) 

 may be considered as being the resultant of two angular veloci- 

 ties, measured, one in the plane of deflection, the other in the 

 plane of sight. The instruments which have been invented in 

 order to deal with solution (1) have been mostly based on this 

 resolution of speed. 



At this point it is important to note that the angular velocity 

 of a flying machine moving with a uniform hnear velocity changes 

 value every minute, except in very exceptional and very im- 

 probable cases; for example, the case of a flying machine which 

 might happen to be revolving around a vertical passing through 

 the eye of the observer. Consequently, the measurement of 

 angular velocity taken at a given time can be considered as 

 available only during a very short while. 



Supposing even that the angular velocity measured at the 

 very moment of the shot could be applied to extrapolate for the 

 point which the projectile ought to reach, and this is question- 



