32 



ASTRONOMICAL and 



latitude, in V 48" was 1". 546 ; from 

 the difference 



liicli subst 



0". oor 



3nce of the parallaxes in latitude in that time, and 

 wc s :;. 1 have 1''. 539, for ^ 's visible motion in geocentrick 



latitude. In V 52", ^ 's true geocentri 



:k 



motion 



1 



With these visible motions in longitude 



was v. 003 ; from which substract the difference of parallaxes 

 in latitude, 0". 004, and we shall have 1" 599, for ^ 's visible 

 motion in latitude, 

 and latitude, we obtain 10". 594 for ^ 's visible motion in 

 his path upon the Sun's disc, in 1' 48", and 11". 061, for his 

 motion in 1' 52". 



The mean of 10" 594 and 11". 061, the motion of ^ in 

 crossing the Sun's limb, at the ingress and egress, is 10". 827; 

 the half of which, viz. 5". 414, being snbstracted from 806. 

 105, half the transit line, between the two external contacts, 

 -will leave 8G0. 781=:lialf tlie transit linej between ^\s cen- 

 tral contact = Ni; or Nr. Let the observed semidiametcr 



■ 



of the Snn= 972^''. 125j be diminished 4/\ 6^ for irradiation 

 or inflexion^ and we shall have 967^^ 625; for liis semidiani- 



I 



eter, to be used in these calculations ; this is = O i or O r. 

 Therefore, in the right angled plain triangles, O ^ 'N and 

 O M N, we have the hypothenuse, O i or O r, and side, ^ N 

 or M N, to find side O N ; whicli is obtained by multiplying 



V 



gether the sum and difference of the hypothenuse and 



and 



extractin^r the 



square root of the product, which 



ea- 



sily done by logarithms. Thus 0N is found = 442". 071. 



Having found G N, let us assume 5" for tlie semidiametcr 

 of 5, which added to the Sun's semidiameter, diminished by 

 inflexion, will give 972". 665, for O ^ and 5 M; and sub- 

 stracted, will give 902'^ 665, for O s and ^^ x ; from which we 



may 



