‘and a Method of difcovering the Longitude. 383 
ing and confequent inveftigation I went through, would be 
unneceflary here. The refult, which I have long fince ex- 
plained to many individuals, I now, in as brief a manner as 
the fubject will admit of, lay before the public, not doubting 
that an obje&, which actually tends to the enlargement and 
perfection of fcience, and, in my opinion, to the benefit of 
navigation, will find favourable reception, inveftigation, and 
experiment. 
Method of difcovering the Longitude, the Magnetic Inclina- 
tion-and Latitude of the Ship beng given: 
Prope the Firft, being the Tazory. 
To determine the Latitude and Longitude of the Magnetic 
Poles, and, in confequence, for the purpofe of difcovering 
the Longitude, to afcertain a Firft Meridian, 
Let N (Plate VIII.) reprefent the north pole of the earth, 
M the magnetic north pole, S Smeerenberg harbour in Spitf- 
bergen, and L London: alfo, let arches of great circles be 
drawn from London to the north magnetic pole, to the north 
pole of the earth, and to Smeerenberg, and alfo from Smeer- 
enberg to the north magnetic pole. There will thus become 
formed three fpherical triangles, which are refolved as fol- 
lows :— 
ift, In the triangle NLS are given the fides NL and 
NS, being the co-latitudes of London and Smeerenberg, and 
the included angle LN S being their difference of longitude, 
to determine the angle of pofition N LS and the third fide LS, 
ad, In the triangle LSM are given the three fides LS, 
(juft found) LM and SM (LM and SM being the magnetic 
polar diftances correfponding to the correct dips at London 
and Smeerenberg), to determine the angle MLS, from 
which fubtracting the angle NLS lately found, there re- 
mains the angle of pofition NLM, 
Laftly, In the triangle MLN are now given the fides 
LM and LN, and the included angle MLN, to find the 
angle LN M, the longitude of the north magnetic pole (and 
the meridian of the earth pafling through the magnetic poles 
and 
