‘ 
DECLINATION. 
of ed shovesnentioned "ne, and the lines a weft declina- 
tion are on its convex _ advan onfiderable ex. 
a t with nearly the fam c] 
: but, as you come on this hde of the tropic of 
Cae the lines of weft deel ination, in both charts, are 
the Tudtan fea, 
and in the fea between the pee of Madagafeur end the 
fouth pole, the declination i:mes are vafily more inregular. 
There is one remarkable eee to be obferved with 
re[pe e& to the Hi of declination on tiefe charts, which 1s 
that they ne rofs each other. 
Tn the Be ae Moses for the year 1757, the celebrated 
Mr. Euler publifhed his refearches on the macnetic needie, 
together with a map containing the fate of the declinaté ‘onl 
lines at about the middle of the lait century. 
to this author, the north magnetic pole of -— 85 
at that time, to have been fitu ated n minece ie 
by Cape St, Lucar, the fot point of Cali- 
and 0° north, 
e curvature a3 th 
the Eat 
oes ee, Mr. Wile cke of Secden alfo publifhed 
a declinatron map, wherein the lines ef declination differ 
confiderabiy from thofe of the preceding maps. 
Betides oe - eg moft accurate charts of particular 
, &c. generally contain the declina- 
the 
of the je lnaecs 
lines are Ha principally by eoaeaure, having not above 
two or three points only afcertained, and thofe probably 
not in a very accurate manner; fecondly, that the declina- 
tions at thofe points have been oblerved at different times ; 
and thirdly, that though made in the moft accurate manner 
imaginable, thefe charts cannot - a for more than a 
very limited number of years mpendious - of the 
general movement of he declination jines is given by Dr. 
Lorimer in the alse 
“At Lon don and Pais, die the moft accurate wea 
vations have been made, towards the latter end of the 
gradually decreafed; fo that in lefs than an 
undred years afterwards, there was no declination at all in 
se seven Paice 1657 at Lordon, and 1666 at Paris, 
welt declination began, and has e 
F th etnies i. uc 
nation, New like t 
tionary ; alee aifo to the dienateas of the inferior 
p’anets, at one time it is to the eaft, and at another time 
to the ih aiternately. 
‘© We may farther nn that the declination lines of 
gradually eaftward, the Tines of eaft declination receding 
be hake it, Nas the lines of weft declination have gradually 
follow 
« in co fouthern hemifpheré, however, it is quite other- 
wife 5 for, ahcut the latter end of the fixteenth century, 
p 
hich declinati - in oe ealtward or ea ; gree 
aisaily increafed to a n degree, and then in the fam 
manner decreafed to nothing, acai to he caltward of 
Java, one of the Eaft India iflands. 
‘© The declination in the Pacific ocean has not as yet 
(1775) been fo fu'ly afcertained ; only in general we find, 
that the declination 1 is eatteriy o over moft part of that exten- 
adually move ha 
thofe “lie es in the ids hemifphere is hen we 
eaft.? 
III. We thall now proceed to treat of the theory of ma 
netic declination, and of its variation ; previou fly to which ‘t 
dia earth is a valt magnet, 
en ee with all the properties which have been pais 
in common magnets. sae needle owes its 
eat magnet 
other, but in any other oftion It may alfo have more 
than two poles. 4. The — of the needle muft ae 
coincide with, or deviate from, the meridian, — ng a 
the ie ata ‘poles of the earth ae to be fituated. re 
AGNETISM of the Eart 5. The pow coke a magnet is 
sialic by heatin is increafed ad oe j a 
owever, withi net limits, 6. The 
iron and the m 
lightning, of violent winds, of the eruptions of volca- 
— and of earthquakes. 
hat the earth, on accoent of its containing immenfe 
maffes of iron, and other ferruginous minerals, is a valt and 
irregular magnet, has occurred to a variety of -perfons al- 
oft ever fince the difcovery of the magnetic needle; and 
that as fuch it muft a& he needle. tD alley, 
ideri i mines, 
movements of the needie were occafiened by the actio 
large magnet placed in or near the centre of the earth, fo 
li as 
, 
