Errors in Azimuth (by Solar Observation > for 1 Minute Error* in 

 Declination and Latitude. 



Azimuth observed with erroneous declination or co-latitude may be cor- 

 rected by means of this table by observing that for the line of collimation set too high 

 the azimuth of any line from the south paint in the direction S. W. N. E. is found 

 too small in the forfnoon and too large in the aftfrnotm by the tabular amounts for 

 each minute of error in the altitude of the line of sight. The reverse is true for the line 

 tet too low. 



Theory 



In his path along the ecliptic, the sun occupies an angular 

 position with respect to the equator and other elements in the celes- 

 tial sphere which can be very accurately ulculated in advance, and 

 for which tabular values, called the Solar Kphemeris, can be prepared 

 years ahead of time. 



These conditions being known, it is not difficult, by use of the 

 graduated circle and spirit levels, to set the main telescope parallel 

 to the plane of the earth's equator and to establish a relationship 

 between the two telescopes that shall be equal to sun's declination 

 for any particular hour of any particular day. The solar telescope, 

 revolving on an axis that has been set parallel to the earth's [ 

 will not, and cannot, follow the sun in his diurnal path unless the 

 main telescope is in the plane of the meridian. 



This process constitutes a: .\\ solution of the 



spherical triangle for the determination of the d >f the line 



XT, Fig. 93, or the projection of that line on the surface of the earth. 





