AIR NAVIGATION 



451 



short distances an angular error in direction of 2° must be expected. ^^ 

 This angular error increases with distance and, should the signal be 

 sent from a region in darkness to a region in daylight or vice versa, 

 may be as much as 90°. Nevertheless it is probable that the method 

 will eventually be perfected, as it is applicable to all regions; and 

 when this is done a complete solution of the problem of navigation 



WoRKED-OuT Example 

 (a) Finding Position 



Place 



Time (Greenwich Apparent 



Time) 



Observed altitude .... 



Declination 



Altitude - Declination 



Station i 

 Start OF Flight 



Point Barrow 



22 h. 



23° 



Station 2 

 100 miles 



on course 



23 h. 

 40° 21' 



23° 

 17° 21' 



Station 3 



200 MILES 



on course 



oh. 

 37° 01' 



23° 

 14° 01' 



Station 4 



300 MILES 



on course 



I h. 

 32° 07' 



23° 

 9° 07' 



Position line is then drawn 

 (b) Finding Direction 



in the polar regions will be provided. As an example of this suppose 

 A and B, two radio stations sending out regular signals, are both situ- 

 ated on an important aerial trade route. An aircraft at A picks up 

 the signals from B. Then all the navigator will need to do in order to 

 reach B will be to follow the direction indicated. 



Nevertheless, this perhaps is looking too far ahead; other methods 

 ■of direction finding are being used at present and will probably con- 

 tinue to be used until the period of exploration is over, in spite of 

 the fact that the airship Norge during her polar flight obtained checks 

 on position by means of radio signals sent out from Kings Bay, Spits- 

 bergen, and Nome, Alaska. 



12 An angle of 2° at 100 miles subtends an arc of about 3^2 miles. 



