LONGITUDE. 



Difference 



Half fum 



Half difference 

 P 's apparent altitude 

 J 's true altitude 



O's apparent altitude 



O's true altitude 



79 42 a 

 46 19 18 



39 51 ' 

 39 3 4 

 39 47 •» 

 32 34 47 

 32 33 25 



Half difference of true altitudes of O and ]) 3 36 56 



42 51 29 



3 



Log. fine 



Log. fine 



Co. ar. loff. cofine 



Log. cofine 



Co. ar. log. cofine 



Log. cofine 



Log. fine 



Log. tangent of an arc 



9.8592754 



9.80671 14 

 0.10981 14 

 9.8855952 

 0.0743564 

 9-925 7539 



2)39.6675037 



19.8307518 



8.7997641 



- 11.9309877 Tang. N. 



Correfponding log. cofine N 9.9981254 

 Log. fine - - 9.8326264 



85 42 58 True diftance required. 

 The formula for the above method is nearly fimilar to that of Borda. It is, 



iin. i (A-n H^ 



^/fiiTl {J {a ^ h) fin, i {d ^- {a ^ h) cof. A col. H ^ ^^^ ^^^ , ^ ^ iin.l(A^H) 



cof. a cof b 



cof. N. 



Example HI. Dunthorn's Method. — Let the apparent diftance of the fun and moon be 86= 10' 19", the apparent 



altitude of the fun 32 34' 47", that of the moon 39 3' 4", and her horizontal parallax 58' 28". What is their true 

 diftance ? 



Log. from Table IX. 

 Log. from Table X. 



9.995526 

 10 



Moon's apparent altitude 

 Sun's apparent altitude 



Difference of apparent altitudes 

 Apparent diftance 



Example 



