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



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



<P' 



-NT 



= C COS + IN . 



A' <p cos 8 



is' cos & sin f . - x . 



-~ (1 2 sin D) sin f . 

 A ?! cos 



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



- = A' (c cos f + N) cos cosec ff . 



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 



R 



+ d tan 6 ~S 



A'H 



E 

 A'H 



+ d tan ff = N', 



where 6 and & represent the true Dip N and N' the computed values at the two geographical 

 positions. 



