378 ISix. W. J. TMacquokn Rankine on the Azimuth of a Star. 



The following is the geometrical construction corresponding to the 

 equation 5. Fig. 1 : — 



Ml 



Draw a straight line, OM, to represent the magnetic meridian, in 

 which take any point, o. From o, set off on the line M, o C = C, the 

 mean of the cosines of the apparent bearings of the object. At c erect 

 C 3 perpendicular to o ii, and make c S = s, the mean of the sines of the 

 apparent bearings. Round the point s, with a radius = A, describe an 

 arc of a circle, to the left of s if a is a positive quantity, to the right if 

 A is a negative quantity. From o draw o B touching that arc. Then is 

 the angle MOB the true magnetic bearing of the object. 



Note on the Approximate Determination of the Azimuth of a Star by Geome- 

 trical Construction, its Declination and Alti'.ude, and the Latitude of the 

 Place of Observation being given. By W. J. Macquok]n' Rankine. 



To solve this problem geometrically, it is necessary to have a gra- 

 duated circle drawn on a large flat piece of card-board. The drawing 

 instruments required are a large pair of compasses, and a long and 

 accurate straight edged ruler. The larger the circle, and the more 

 minute the graduations, the more accurate will be the result. 



Let E II' E H be the graduated circle, whose centre is at o. This circle 



