366 



Astronomical and Nautical Collections. 



error which could arise from the use of the simple proportional. 

 This error, even with 21'' 56"" of interval with the same latitude, 

 and the utmost value of dZ>, would amount only to ^of a second. 

 But as such circumstances are very unfavourable for the deter- 

 mination of the time, they do not offer themselves to us in prac- 

 tice, and it follows that in cases which really occur, the use of 

 the table, taking the simple proportional, is accurate to the tenth 

 have asserted in the preceding memoir. 



San Fernando, 1st May, 1820. 



Translation finished at Liverpool, 

 24th December, 1821. 

 A. L. 



ii. An Essay on the easiest and most convenient method of Cal- 

 culating the Orbit of a Comet from Observation. By William 

 Olbers, M D., 8vo. Weinar, 



(Continued from Vol. XII. page 151.) 



§.58. 



Supposing now adc to be the projection of the chord of the 

 earth's orbit on the plane perpendicular to the middle position of 

 the revolving radius for the earth ; and aA, dD, cC, projections 

 of the lines of direction on the same plane, 



