328 Astronomical and Nautical Collections. 



The conjunctions of the Moon with Mercury and Venus on 5th 

 January; with Venus on 5th September; with Mars on 10th 

 August; and with Saturn on 3d July will not be occultations any- 

 where on the globe. 



The method of computing an occultation, given in these collec- 

 tions, No. XX, Art. 3, is the same in principle as Du Sejour's, 

 which is fully detailed and demonstrated in his " Traite Analytupie 

 des Mouvemens Apparens des Corps Celestes." It is there shown, 

 (Vol. I. p. 270), that the supposition of the portion of the moon's 

 orbit, described during an eclipse or occultation, being a straight 

 line, causes insensible errors only. An error of greater magnitude 

 may arise from the horary motion being esteemed uniform, while it is 

 generally variable ; but this error can be easily corrected by using 

 the horary motion corresponding to the middle of the particular 

 interval under consideration. 



In the precepts for computing an observed occultation in the 

 article alluded to, reference is made to the denomination (North or 

 South) of the moon's nearest approach, which is not set down in 

 the elements published in the Nautical Almanac, as it is always the 

 same as that of the difference of declinations at the conjunction. 



