Theory of the Situation of the Magnetic Poles, &c. 379 
alone their fallacy or utility could be difeovered; they of courfe 
engaged much of my attention, and gave me the fulleft op- 
portunity of exper ieheing; with regret, the many imperfec- 
tions of what is called the azimuth compafs... This inftru- 
ment, though fufficiently accurate to enable us to obferve 
the variation fo as to enable us to fteer the fhip without any 
material error, with the precaution of always ufing the fame 
compafs by which it is taken, is far from being of fuch 
aconftru€lion as to give the variation with thiat degree of 
precifion which fhould attend experiments on which a theory 
is to be founded, or by which it is to be tried. The obferva- 
tions taken in this. voyage will fully evince this by their great, 
variations from one another in {hort intervals of time; nor 
is this difagreement of fucceffive obferyations peculiar to high 
Jatitudes, and to be attributed to a near approach to the Pole, 
as I found it take place even upon the Englifh coaft.” 
Mr. Wales, F.R.S. Mafter of the Royal Mathematical 
School in Chrift’s Hofpital, Secretary to the Board of Lon» 
gitude; &c. in page 49 of the IntroduGion to the Original 
Aftronomical Obfervations ntade in the Courfe of a Voyage 
towards the South Pole, and round the World, in his Maje- 
fty’s fhips the Refolution and Adventure, in 1772, 17735 
1774, and 1775, by himfelf and Mr. William Bayley, now 
Matter of the Royal Academy at Portfmouth, pubbthes by 
order of the Board of Longitude, fays : 
<¢ J cannot pafs over this article without making a tema 
or two on the irregularities which we found in the obferva~ 
tions made with thefe. inftruments in the Channel of Eng- 
land: the extremes of the obferved variations were from 
193 to 25; and all the way from England to the Cape of 
Good Hope 1 frequently obferved differences nearly as great 
without being any way able to account for them, the dif- 
ference in fiasiatiors being. by no means fufficient. Thefe 
irregularities continued after leaving the Cape,” 7. ¢. they 
continued throughout the voyoge. Bat thefe irregularities are 
trifling compared with thofe 
Of the Dipping Needles, or Compafs. 
Thefe inftraments were fo imperfect in principle, and thé 
obferyations made with them fo uncertain, that, excepting 
3C a the 
x 
