K . 



!^P5iical .„ 



or^ 





■^wVr 



^^U t,^ 



ft . 1 





IS >, 



er^ - 



'T_ 





<-«u 



n. 



IKS 



uy, 



- ^4 , ; 



'^^er.acdift^'. 



^ * 



** U^ 



nbas b 



tf *^^ 1 



■^ 



aa r. 



• nrsapi 



WA-t\, 



R 



of 



Appendix.] 



TERRESTRIAL MAGNETISM 



49 



C—(=id is the deviation or error of the standard compasb caused by the 

 ship's iron when her head is on the point C ; and finally A, By C, D^ E, 

 c, d, and A', are coefficients to be employed in calculating t)ie cor- 

 rections applicable to the magnetic observations of the declination, 

 inclinatioBj and force made at sea in any part of the globe. 



7. For the corrections of the declination A, B, C, D^ and E are required ; 

 they may be computed by the following rules : let the 32 points of the 

 compass be nostbered from 1 to 32, beginning with N.byv\\rrl; 

 N. N.W.— 2, &c., and going round by S.=i6. to N.i=:32; and let the 

 deviations observed on the diflerent points, when the ship is swung^ be 

 designated by 5 with the number attached which shows the point to 

 which it refers : as for example d^ will be the deviation at N. by "VV. ; 

 §2 at N. N. W, ; 5,6 at South ; and §33 at North. Then, if the devia- 

 tion has been observed on the sixteen principal points, we shall have the 

 values of 5 at all the even-numbered points, as d^, -5^, §^,, &c, to ^33 ; and 

 of these values all those in which the North end of the needle is dra-^^n 

 to the westward by the ship's attraction will have the sign + prefixed: 

 and all those in which it is drawn to the eastward the sign — ; the si^ns 

 must be attended to in making the additions which follow : 



Y -_ 



caret u.' 



". *-- 



3 ^ct 



liservations 1 

 - -♦ ^« port, f- 



B= -0478 (its log 



2-6800) 



{h 



/ 



+ ai55 (its log 



+ 1(5 



8 



^24)' 



1^0625) 



ih 



+ s ^ 



mJ 



^30 + ^14 ^ ^is], 



+ ^0881 (its log = 2-9464) { a. -- S^g + 5 



i& 



S 



26 



d 



10 





■lie at 



r" 1 



J ' -I 



jSttT 



"isai; 



vii:.^'5 



the ^ ■■ 



ID 



V 



.1 



'vr 



forfli 



ul-' 



'.'M 



IS 



tbe w- 

 obsef ^ 



.. of '^^ ■ 



.»^ 



h 



\ 



-.elf 



T ^ 



/ 



C = -1155 (its log = i'0625) {n^ + -5.,, 

 + '0384 (its log =¥^9464) {5. 4- 5 



+ '0478 (its log --r: 2^6800) {§5 + S 

 + I (5a2 - 5ia). 



26 



'26 



D = -0884 (its log = 2-9464) {t, - ^^o 



6 



e 



5. 



26 



5.0 ^ 



+ ' 



5 



{5 



5 



sa 





E 



8 



6 



s 



10 



5. 



22 



+ 1 {5.« + 5 



16 



5o- 



} 



K^t* 



B 



l4 



B 



12 



B 



iO 



^ibI? 



B. 



•20 i ? 



^^}f 



^u + ^m + 



0884 (its log = 2-94C4) {d. + ^30 + ^u + ^ih 



If the deviations are greater than 7^ or 8°, the sines of the a^^les of 

 deviation should be used in the formuhe instead of the angles themselves. 

 Where time will not allow of observations being made on the ^'^tcen 



D 



