52 



TERFtESTRIAL MAGNETISM. 



^ 



[Sect. II. 



\ppei 



-3 





^3 - 



= A + B3 + C5 + D« 



+ Ea 



^w- 



= A - B3 + C5 - n 



+ Eg 



^13 = 



= A + B3 - C, - D, 



+ Ej 



^19 = 



= A - B3 - C5 + D, 



+ E2 



84 ^ 



= A + B, + C^ + D 





5^8 = 



= A - B4 + C4 - D 





h,'- 



= A + B4 - C4 - D 







- A -> B^ - C4 + D 





55 = 



= A + B5 + Cg + Dg 



— E2 



^'27 ~ 



= A - B, + C3 - De 



-E, 



Sn = 



= A 4 Bj ~ Cg — Dg 



-E, 



^ei = 



= A - B5 - C3 + Dg 



-E, 



86 = 



= A + Be + C2 + D^ 



-E, 



5gQ = 



= A - B« + C, - D4 



-E, 



8]0 - 



= A + Bg - C2 - D, 



-E, 



5«r = 



= A - B« - Ca + D, 



~E, 



8, 



i5 



A + B, + Ci + D^ 

 A - B7 + Ci - Dg 



- C. - D, 



A + B7 



S 



23 



A 



B7 



c, +n 



E 

 E 

 E 



E, 



6 



(5 



6 





A + B 



24 



A 



B 



E 

 E 



f 



If the aKgles are greater than 7° or 8°, these fbrmulse give the sines of 

 the angles of deviation instead of the angles. 



8. For the correction of the inclinations observed at sea the co- 

 efficients c and d may be computed from the disturbances on the several 

 points, shown by the observations of the inclination with Fox's apparatus 

 when the ship was swung in harbour, by the formula : 



ccos f + Jtan 9 



(1 



D) sin ^cosec C tan 6^ 



for all other points than North and South, and "with the ship's head 

 North or South, by 



c 



(cos C + B) sec ^ tan d^ ; 



ohserving that the v^ilues of ^ employed should be calculated by the 

 declination-coefficients. With the values of c and d thus obtained, 

 tables for the correction of the inclinations observed on different courses 

 at sea in all values of may be computed by the formula : 



tan 



/?/ 



e 



CI - D) 



. (cos C T d tan d) sin C c^^^ec C 



obsen 



is pea: 

 lated 1 



sea, «a 

 of the 

 the di 



shore 



J 



tailed 

 of the 

 forma 



the fiti 



the im 



10. 



gimba 

 at the 

 ixiaj b 

 obser - 

 andD 

 no dis 

 coeffij 

 tioa 



defler* 

 the 







mt 



