which ivill happen on September 7, 1820. S9 



of the sun: and they are as follow. The ecliptic conjunction 

 will take place on September 7, 1820, at 



V\bV. 37",3 P.M. apparent time' 



or !^ at Greenwich : 



1. 49. 26, 2 P.M. mean time 



} 



And, at that time, we sliall have tlie 



True longitude of the luminaries . . . . 5.14. 47. 40,7 



True latitude of the moon (north) 44. 39,4 



Moon's horary motion from the sun „ 27- 1,7 



horary motion in latitude (decreasing) . . 2. 42,0 



horizontal parallax 53. 53,0 



semidiiimeter .. .. 14.41,0 



Sun's seniidiameter 15.54,8 



horizontal parallax 8,7 



declination (north) 5.59.41,0 



From these elements it may be determined that the moon's 

 shadow first touches the earth's disc at 1 1*^. 23' A.M. apparent 

 time at Greenwich, in N. lat. 59°. 43', W. long. 90". 50'* ; and 

 that it finally leaves it at 4^'. 39'| P.M. apparent time at Green- 

 wich in N.'lat. 3°. 21', E. long. 20°. 25'. Consequently the 

 total duration of the general eclipse to the inhabitants of the 

 earth will be about 5"^. 17': but, at no one place in particular 

 will the duration be much more than half that time. 



The central path of the moon's shadow across the earth's disc, 

 which is the most material circumstance in inquiries of this na- 

 ture (since it serves to point out those parts of the world where 

 the eclipse will be seen annular) may be determined with consi- 

 derable accuracy from the principles laid down by M. Delambre 

 in his Traile d' Astronomie (vol. ii. page 384) : and, agreeably to 

 the formulae which he has there given, I have carefully computed 

 the following table, which shows the several points (expressed by 

 positions of latitude and longitude) through which the centre of 

 the moon's shadow will pass in its progress across the earth's disc, 

 at the several times therein mentioned. The first column de- 

 notes the apparent time at Greenwich, at the moment when the 

 centre of the moon's shadow passes the given points laid down 

 in the second and third colunnis : and the last column shows the 

 corresponding apparent time at those places. 



• All the Longitudes in this memoir are rcUoiicJ frcin the meridian of 

 CiXcir.vich, 



Jpparent 



