WEIR S AZIMUTH DIAGRAM. 



291 



be seen on Fig. 2 without any explanation. If, therefore, it were 

 necessary, instead of moving the line, to imagine the position of the 

 observer' to be shifted in the opposite direction, it is evident that he 

 -p, „ would have to be re- 



■ ■ moved to a distance 



equal to r X the tan- 

 gent of the declina- 

 tion. A scale of tan- 

 gents laid down above 

 and below the eqiiator, 

 as Fig. 3, would there- 

 fore represent the 

 position of an observer 

 at the equator for each 

 degree of declination, 

 and if the line C E 

 were divided into a 

 scale of sines repre- 

 senting the sun's posi- 

 tion on it for, say 

 every fom-th minute of 

 time, we would have 

 a diagram by which 

 the sun's bearing might be calculated at any time, and with any 

 declination, as seen by an observer at the equator. 



As I before showed, with the help of Fig. 1, that an ellipse 

 representing the sun's path in any latitude would have its major 

 and minor axes of the same relative dimensions as 1 : sine latitude, 



I have constructed a 



Fig. 4. 



diagram on this prin- 

 ciple (Fig. 4), the 

 ellipses being drawn 

 for every tenth degree 

 of latitude.' and the 

 position of the sun on 

 them shown for every 

 twenty minutes by the 

 vertical lines. The 

 sun's true azimuth 

 may be taken from 

 this diagram for any 

 latitude and any time 

 as long as his declina- 

 tion is 0°, but if de- 

 clination be intro- 

 duced into the pro- 

 blem it becomes more 

 difficult to solve, as I 



