DECLINATION. 
us to form a fort of nucleus to the earth. He alf. Ve 
pofed that this oe nucleus hada seca l ee mo 
tion, whence arofe the declination and its variatio 
Epinus en pear nearly the fame fae but “inftead of 
admitting the peculiar motion of the 
that its magnetic Gee only oS d ee 
fioned the variation of the 
a « Itis mentioned by Mr. 
De Lalande, that Mr. ias Mayer fent him an extra 
f an unpublithed memoir es his, which contains his hypo- 
thefis concerning the magnetical movements. Mayer 
a very feral magnet, having two Rie es, ee 
within 04 earth. The centre of this magnet is removed, 
he fuppofes, from the centre of the a - one fe. 
venth of its radius, aad recedes from it each year one thou- 
tre of ae earth through that of t 
pal itude, and 17° of coe an ud 
fes 8’ every year, and the latitude 14) 
Mr. Bio tot has likewife endeavoured to exzlain, by mea ng 
of an interior magnet, all the eee of t ic 
needle, that have been obferved by iumboldt in his 
8, 17505 
€ : oate pani 
travels. He has attemnted to eee. from the obfer- 
vations of La Peyroufe, and Von Humboldt, all the ele- 
ments e magnetic th at th d he has 
given the neceflary formula for calculating what the decli- 
nation and dip ing . the needle (fe ipeinG Needle) 
Bu 
according this. formula, have not nas 
with the aGua obfervations made by Meffrs. Humboldt, 
and oo in their travels through Italy, Fraace, and 
Germ 
cae perfons have Attributed the movements of the 
needle i the action of celeftial ea or to fome aerial 
current of magnetic or eleGrical flui 
Upo attentive canfideration all the particulars 
that ie been afcertained by means of > and long 
eontinued obfervations, the idea 
able internal m ems to be the me warranted either 
analogy, 
obfervations, 
magnet fee 
aah ) an fede muft contin ally tend 
alter the quantity a se paciaucenn tae actions upon the 
magnetic needle ; tter muft, 
the the lat 
according to the Ariel philofophical rican ng, be derived 
from thefe adequate caufes, without recurring to fuppofi- 
tions purely chimerical. 
Dr. Lorimer’s theory, which endeavours to explain the 
movements of the magnetic needle by the action of the folar 
heat upon the eatih, Being the moift rational a ft i 
ligible, we fhall conclude ‘his article with a ftatement of it. 
all the ferruginous 
at the magnetic fase fhould 
therefore be confidered as ae eee of the powers of thofe 
a fubftances. Thefe poles muft Gage change 
eir places, SES ag ~ a ar fubflances is 
affeeied d; and if, with Mr. Ca e allow that the general 
caute of the Cara a ‘ails en the fax s heat in 
of a moveable or immove-.. 
" fome time after the fun has pa 
the forenoon aad afcernoon of f the fame day, i it will naturally 
occur, that t ufficient 
to produce ae cecal variation of the magnetic needle 
for any ft confider, that 
re) 
ASLHUCG , 
antly moving fr fro 
that in other parts of the world it has nme its motion 
with equal conftancy. 
«As we mutt therefore admit, that the heat in the diffe- 
rent feafons depends chiefly on the fun, and upon the whole, 
- that the months of July and Augutt will probably be found 
the hetteft, while January and ruary are the coldeft 
) f the ; and that the temperature ther 
t 
months falls into the refpective intermediate degrees ; though 
from calculation we can fcarce pretend to ages the abfo- 
lute heat of any particular month or day ; hag aa cons 
a the influence of heat upon magnetifl 
nt 
itfelf , tury, t 
gularity thereof beco:nes fufficientiy oar Tet woul 
therefore be idle to fuppofe, that fuch an influence could 
be derived from an uncertain and fortuitous caufe; but if 
it be allowed to depend upon the conftancy o n’g mo~ 
tion, and this i s to be a caufe fufficient to explain the 
phenomena, we fhould, agreeably to Newton’s firlt rule of 
puloiephigae, look no farther. 
“* As we therefore confider the magnetic powers of the 
ange As be concentrated in the magnetic poles, and that there 
urnal variation of the magneti e 
ae perform fal diurnal revolution proportional to fuch 
variation, ae urn again to the fame point nearly. Sup- 
and thee equa 
fle magnetic pote i is anak he will b Nearer to it 
than in any other oppo sie aan he will of 
courfe be the peed en it. Asthe influence of the fun’s 
heat will therefore a&t moft powerfully at the lealt, and lefs 
orcibly the magnetic pole will con 
a 
xis of this elliptical figure will lie north-eafterly in the 
8 
power, the magnetic poles cannot be 
moved back to the very fame point from which they fat out ; 
but to one which will be a little more sale A and eafterly 
eafterly, according t hemi- 
efore 
aaa in which they are iad The figures ther 
ich they de : dese ¢ properly be aati elliptical 
fr a. rth cates pole may by this — ie 
caitin with a ise but conftant motion, more mo 
o the north. eaftward, tillit arrives at the region of fthe ee 
eft cold. 
this manner the variation of the magnetic needle in 
the deals hemifp ere may be accounted for. 
{pect to the vies hemifphere, we muft rec 
that though the lines of declination in the northern 
hemifphere have pane moved from weft to eaft, 
yet in the fouthern hemifphere it is equally certain that 
they have — rom * oe pli ever fince any ob- 
fervations hav ubj-&. Is it pof- 
fible, then, that ee mogeet coed in = fouthern hemi. 
{phere. 
