474 keille: anti-aircraft firing 



able owing to the relatively long duration of the flight, any 

 measurement taken at a moment somewhat prior to the firing 

 of the shot is evidently out of date and has no value whatever 

 regarding the extrapolation desired. 



This is the reason why, after the trials made with instru- 

 ments capable of giving from time to time discontinuous meas- 

 urements of angular velocities, it has been felt necessary to sub- 

 stitute for them instruments for continuous measurements, such 

 as the galvanometric cinemometer. 



This instrument is based on the following principle: A steel 

 armature which turns inside of a solenoid develops a current of 

 induction, the intensity of which is a measure of the velocity of 

 rotation. If the steel armature is secured on the axis of a sighting- 

 telescope pointed at the flying machine, a galvanometer duly 

 graduated will enable one to read constantly the angular velocity 

 of the flying machine. 



(2) The solutions of the second kind are based on the meas- 

 urement of the hnear velocity. A very great majority of these 

 solutions have assumed as an hypothesis that the measurement 

 of the horizontal hnear velocity gave sufficient data for firing; 

 that is to say, that it could generally be considered that the 

 altitude of a flying machine did not alter much during the time 

 of the flight of the projectile. It goes without saying that these 

 solutions also assume as an hypothesis that the speed of the 

 flying machine in regard to the problem of firing can be con- 

 sidered as uniform. This admitted, a measurement of linear 

 velocity, taken at any moment, remains available. 



All the instruments based on the solutions of the second kind 

 have been based on the same principle as that of the plotting- 

 hoard. Some of these have endeavored to draw automatically 

 by simple sighting a continuous track of the course of the flying 

 machine. It seems that it is in fine with this idea that the 

 most handy and useful, if not the most complete, instruments 

 will be found. 



