( 274 ) 



Tlic line A Z, w lücli coiiuccts the centre A of the Earth witli 

 the centre Z of the Sun, ijitersects B jit the point P. We call this 

 point "the projection of the Earth on the Sun" and will determine 

 its track on B. 



The inclination of the Sun's equator on the eclijitic is 7'i3'. About 

 the 4^^' of June and the 6^'' of December the Earth passes through 

 the nodal line. 



Fig. 1 represents i)art of the sidiere B ; EE' is the intersection 



Fig. 1. 



with the ecliptic, QQ thai with ihe SuiTs eipialoi'. On the 4*^'' of 

 June Ihe Earth's projection is in l\,. Throuiih this point we draw 

 the lirst meridian M. In the space of about 25,929 days M has 

 made a synodical revolution and is intersected for the second time 

 by the line A Z (not marked in the diagram) but this time at the 

 poiid 1\, a liltle to the north of the equator. Iji the interval Phas 

 been describing one convolution /*„ B' B" B.^ of it helical course. 



The next points of intersection I\ and B^ of the path of B with 

 the first meridian again lie somewhat more to the north, but about 

 the 4^^' of September the path has I'eached its utmost latitude 7^15' 

 and then gradually descends towards the equator, which on the 6^'' of 

 December it intersects a little beyond P.. 



All the points of intersectioji for one year are marked on the 

 meridian J/ in its tirst position. B^ to B^^ lie in the southern 

 hemisphere. P^^ is reached after 14 X 25,929 = 363,006 days; the 

 sideral year has 365,256 days, consequently P^^ does not coincide 

 Avith Bo ; the track of B intersects the Sun's equator 2,25 days later. 



During the second year, B, in its helical course, passes through 

 entirely different points of our spherical surface than in the first year, 

 and so do the successive annual spirals ; they each time skip an angle 



