386. Theory of t*e Situation of the Magnetic Poles, 
the obfervations of the magnetic inclination, made at anchor 
or on fhore, (and even thefe, as any one may perceive, were 
far from being certain,) no manner of ufeful certitude or 
judgment could arife from them. Mr. Wales, in his de- 
{cription of the dipping needle here fpoken of, and made by 
Mr. Naime agreeable to a plan of the Rev. Mr. Mitchell, 
F.R.S. obferves, in page 50 of the Introduction aforefaid : 
‘© The principal defects in this conftruction are, the diffi- 
culty in placing the wires which carry the two laft men- 
tioned balls in the proper plane, and the total impoffibility 
of knowing when they are fo: moreover, it is very poffible, 
and undoubtedly often happens, that the axis of the needle 
and its two poles do not lie in the fame plane, in which cafe 
another difficulty will arife in adjufting the needle to great 
exactnefs.”” And in page 15 of the Obfervations themfelves, 
Mr. Wales remarks as follows : 
¢ The dipping needle which we took afhore at this place 
(the Cape of Good Hope) was fo much out of balance, and 
fo difficult to get in again, that notwithftanding we both of . 
us (Mr. Wales and Mr. Bayley) fpent all the leifure time we 
had from other obfervations, we did not get it perfe@tly ad- 
jufted before we went away, and of courfe were not able to 
get any obfervations of this kind at this time.” 
Mr. Bayley, in page 217 of the Original Obfervations 
made in the courfe of a voyage to the Northern Pacific 
Ocean, for the difcovery of & north-eaft or north-weft paf- 
fage, in his Majefty’s fhips the Refolution and Difcovery, in 
the years 1776, 1777, 1778, 1779, and 1780, after, as appears, 
much precaution on obferving with, and changing the poles 
of the dipping needle, &c. fays: On the 28th July is men- 
tioned an accident happening to the dipping needle: “ the 
poles were not then changed, as the obfervations afterwards 
appeared regular; neither were the poles changed on receiving 
#t on board, as it was faid to be well balanced: but the not 
doing it at either of thefe times was a great overfight, as we de 
not know the error of the dips with the marked end north, and 
dipping in any obfervations before to-day, and therefore can- 
not correct them according to Mr. Cavendith’s direCtions. 
If we fuppofe the fame error from the firft as on to-day, (the 
mean 
