384 Theory of the Situation of the Magnetic Poles, 
and poles of the earth,) from the meridian of London, and 
the fide MN the diftance of the magnetic pole from the pole 
of the earth. 
The place of the magnetic poles being thus obtained, the 
queftion next divides itfelf into two points of view, namely, 
Whether the magnetic poles or points thus determined are 
ftationary or otherwife? the folution of which depends on 
obfervation and philofophic inference. From obferyation it 
is remarked, in page 121 of the late Lord Mulgrave’s Account 
of his Voyage towards the North Pole, that— 
«© There is no reafon at prefent to fuppofe that, the dip is 
liable to any variation in the fame place at different periods 
of time. It having been obferved at London by Norman, 
who firft difcovered it in 3592, to be 71°.50’, and by Mr. 
Nairne, in 1772, about 72°: the difference between thefe ob- 
fervations, taken at fuch diftant periods of time, is fmaller 
than that found between feveral of Mr. Nairne’s obfervations 
compared with each other; and therefore we have no reafon 
to conclude that the dip has altered fince Norman’s time. 
The care with which his inftrument was conftructed, and 
his obfervations made, leave us no room to doubt of their 
accuracy.” 
Again, Mr. Cavallo, in his Treatife on Magnetifm, p. 65, 
remarks, (fpeaking of the dip,) ‘* Its alteration in the fame 
place.at different times is very fmall; thus in London, about 
the year 1576, the north pole of the dipping needle ftood 71.50 
below the horizon, and in the year 1775 it ftood at 72. 03: the 
alteration of the inclination in fo many years amounting to 
Jefs than a quarter of a degree, which may be attributed to 
the error of the inftruments, fince, as will appear in the fe- 
quel, thofe infiruaments are far from having attained to any 
degree of perfection even in the prefent age.”’ : 
Now, from philofophic inference it will naturally follow; 
that if the inclination of the magnetic needle at different pe- 
riods of time at any one place remain conftant, the magnetic 
poles are ftationary; and if the magnetic poles are fiationary, 
(as appears clearly evident from above,) the meridian thus dif- 
covered is the Fir/f (or only) Meridian from which the lon- 
gituds 
Z 
