( 322 ) 



Finally we will give below, vide pp. 334 and 335, two instances 

 of computation ; one of a case in which the apparent motion of the 

 two satellites was opposed, the other in which it was in the same 

 direction. 



l^t Appendix. What is the maximum duration oj the several occuh 

 tations of one satellite by another ? 



We have seen above that it took 19'"-2 to annul the small 

 difference of the elongations of O'll (2"0). This was caused by 

 the minuteness of the relative motion of the satellites. But in the 

 case that the hourly motions, which we will denote by u and u' , 



x' X 



are absolutely equal, the denominator of the fraction -; is zero. 



