475 



retardations in the air, nor the frame which carries the axis of 

 rotation from being set swinging around its pivots. To avoid an 

 inconvenient agility of the iiand under intiuence of such oscillations, 

 care was taken to secure a slow indication of the currentnieter, 

 which was obtained by making the instrument over-deadbeat by 

 damping, the oscillations of the magnet being made as short as 

 possible, besides which a damping by mechanical friction was applied 

 for so far as coexistent with the requirements of an accurate working. 



If the instrument was adjusted sideways on the aeroplane out 

 of the "propeller-wind" about halfway between the two decks of 

 a biplane an ascension was indicated when the machine flew at level 

 keel, while an ascending was strongly exaggei-ated and a descent 

 was not at all or hardly indicated. This shift in the direction of an 

 ascension in the indications, which was observed in a higher or 

 lower degree in a number of places on the aeroplane is caused by 

 air currents generated l)y reaction from the aeroplane in its quick 

 motion through the air. When fixed at the end of a wing at some 

 distance sideways, the instrument gave undisturbed indications. In 

 this position however the troubles of the oscillations mentioned above 

 were felt more strongly. 



It would be a valuable result if by means of this instrument a 

 systematical investigation could be made of the vertical velocities 

 of those reaction currents produced in the neighbourhood of an 

 aeroplane in flight. 



It is highly to be regretted that there is no possibility in our 

 country of calibrating the scansimeterscale in an artificial air current. 

 When the electrical resistances, the strength of the magnetic field 

 and the sensitiveness of the currentnieter are known, this calibration 

 consists in the research concerning the number of revolutions the 

 screw makes at various velocities relatively to the air. Since the 

 air-tunnel set up on a small scale by the "Kon. Nederl. Vereeniging 

 voor Luchtvaart" could no longer be used, such a testing cannot be 

 executed in our country. 



