NOTES. 



475 



the earth, then Jupiter is in opposition when at O, and in conjunction when at 

 C. In these positions the three bodies are in the same straight line. 



Ffg.SS. B 



NOTK 94, p. 34. Eclipses of the satel- 

 lites. Let S, fig. 25, be the sun, J Jupiter, 

 and a B ft his shadow. Let the earth be 

 moving in its orbit, in the direction 

 EARTH, and the third satellite in 

 the direction abmn. When the earth 

 is at E, the satellite, in moving through 

 the arc a b, will vanish at a, and re- 

 appear at b, on the same side of Ju- 

 piter. If the earth be in r, Jupiter 

 will be in opposition; and then the 

 satellite, in moving through the arc a b, 

 will vanish close to the disc of the 

 planet, and will reappear on the other 

 side of it. But, if the satellite be moving 

 through the arc mn, it will appear to 

 pass over the disc, and eclipse the 

 planet. 



NOTE 95, pp. 35, 48. Meridian. A terrestrial meridian is a line passing 

 round the earth and through both poles. In every part of it noon happens at 

 the same instant. In figures 1 and 3, the lines N Q S and N G S are meridians, 

 C being the centre of the earth, and N S its axis of rotation. The meridian 



