22 THE VOYAGE OF H.M.S. CHALLENGER. 



Page 12, line 17. For computing the coefficient A' the formula become — 



a> sin & v , xr 



Vi - n = c cos C + -N . 



A <p cos 



<p' COS & Sin f ... n • Tw\ • «« 



Hn —- = (1 — 2 sin D) sm f . 



A p cos v y 



13 „ 18, after " A table of corrections for the several azimuths " the formula becomes — 

 — = A' (c cos % + N) cos cosec 0' . 



Note. — N, as well as sin B, should be computed at each base station where the ship is swung. 



After a considerable change of magnetic latitude, especially if one station is near the Magnetic 

 Equator, the proportions due to " hard " and " soft " iron in N may be computed by the two following 

 equations — 



E 



A'H 



E 



A'H 



+ d tan = N 

 + d tan & = N' , 



where and 0' represent the true Dip — N and N' the computed values at the two geographical 

 positions. 



