524 
APPENDIX. 
[ Errors in variation. 
not all ofthose where great differences had been observed, but also that the 
differences themselves were conformable to what had taken place upon the 
binnacle of the Investigator. 
Mr. Wales goes on to observe, “ It is not necessary to account for 
“ these differences in the observed variations in this place, nor yet to point 
out the reasons why such anomalies have not been noticed in observa- 
tions of this kind before. I shall however remark, that I have hinted at 
“ some of the causes in my introduction to the observations which were made 
in captain Cook’s second voyage; and many others will readily offer 
themselves to persons who have had much practice in making these 
observations, and who have attentively considered the principles upon 
which the instruments are constructed, and the manner in which they 
are fabricated. Nor is it at all surprising, that the errors to which the 
“ instruments and observations of this kind are liable, should not have 
“ been discovered before; since no navigators before us ever gave the 
<£ same opportunity, by multiplying their observations, and making them 
“ under such a variety of circumstances as we did.” 
That the compasses, even in the Royal Navy and to this day, are the 
worst constructed instruments of any carried to sea, and often kept in a 
way to deteriorate, rather than to improve their magnetism, cannot be 
denied ; but errors arising from the badness of compasses would not be 
reducible to regular laws as those were in the Investigator, and appear to be 
in the three ships commanded by captain Cook. It seems indeed extraor- 
dinary, that with the attention paid by Mr. Wales to the subject, he should 
not have discovered, or suspected, that the attraction of the iron in the ship 
was the primary and general cause of the differences so frequently observed ; 
nor have perceived that the differences varied proportionally to the direc- 
tion of the ship’s head and to the dip of the needle, and were of an oppo- 
site nature in the two hemispheres. But it should be recollected, that the 
apparently contradictory phenomena which occur in most branches of 
science, frequently bewilder the inquirer in a labyrinth where pursuit seems 
to be hopeless ; and that when one general cause is found to explain all 
the contradictions, to have hit upon the clue appears so easy that anyone 
might have perceived it: the inquirer himself is not less surprised that 
it should have escaped him so long, than pleased at his final success. 
