éautious perfons patiently awaited the refule of experience ; 
but the refult of a€iual experiments a proved the ims 
practicability, or the infufiiciency, projects, which 
were of courfe gradually negledied, ae were laftly even ri- 
diculed by the facetious De ean Swi 
of calculation is to dete 
o 
ae) 
= 
=) 
&. 
.o] 
yp 
ae 
=) 
2, 2 
1 
> 
might pafs through the po a large magnet, and 
whic cra {mall magnetic needle may be a tangent at 
any point of its courfe. Or afe of the earth, to catcu 
e 
late ie inclination which the needle muft have in any uae 
cular point of its furface. ‘The data, however, upon which 
thefe calculations mult be grounded, are uncertain. "The 
magnetic needle is ated upon by both poles of the earth, 
and the law of that ation is by no means well known ; 
though it appears, both from ce penmcus and see 
that, moft probably, the force of each pole varies in the in- 
verfe duplicate ratio of the diftance. See Mr. Tene 8 
experiments and calculations in the Memoirs of the Academy 
of Berlin f for 170% and his fecond differtation in ~ 22d 
our readers to other 
are the 
not {well this article by the introduction of oe icate ave 
gations. 
In fhort, it appears, from the concurrence of all the moft 
accurate experiments and obfervations that have been made 
upon land as well as at fea, 1{t, that the earth is not an uni- 
form or regular magnet, but a very irregular cue; for the 
ferruginous a of it, oon the joint action of which the 
magnetifm of ti whole arift eSy 
it 3; whence it ants that according 3 as the magnetic “needle 
is nearer to or farther from any ferruginous fatter, o it i3 
ore or lefs influenced b , the magnetic poles 
South, and Jongitude 92° Eaft. Wilcke of Stockholm,” in 
his indication chart, in the 33d vol. of the Swedifh Memoirs, 
places the nort 
Bafiin’ s B 
the fouth pole in la t. i Jong. planie 
he 
{phere b cademy 0 ces a * Pavis for 1786, 
places the magnetic equator fo’ as to interfeét the earth’s 
equator in long. and 155° from the Ifland of Ferro, 
with an inclination es 12° nec anys gs : medal a great 
circle. But we are not intorm ority,; nor 
does this {tatement agree with the obfetation of the di ping 
made by Bnitifh navigators. Mr. Churchman has given 
fketch of a planifphere with lines which sea on called oan 
lels of the dip. ‘Thofe parts of each ate | have ae 
— by obfervation, are marked b fo that w 
udge of his authority for the whole pesehoes The 
and 195° Greenwich cee at an angle of a 
nearly cles of etic inclination are not pa- 
sane being confiderably nearer to each other on the fhort 
meridian Auer on its oppofite. 3dly, the magnetifm of the 
ear tions 
equato 1, & c. are fubje a gra 
ation, which, in all Set bile ae from the irregular 
DIPPING. 
heating and cooling, from the formation and decompofition 
of the different internal parts of the earth, and perhaps from 
other ca 
Notwithtt tanding the failure of the advantages which were 
expzCted from the dipping property of the magnet, it muit 
be acknowlcdged, that the dipping needle, which fhews the 
above-nentioned property of the magret, feems, upon confi- 
erie a to be the principal inftrument, from the indication 
of 
a 
curate, and at the fame ona leatt expenfive, inftruments may- 
be contrived for the purpofe ; and that numerous as well as 
accurate obfervations may be ‘made with them i in every part of 
the werld. 
ica ee is an inffrument which fhews the ir- 
clination of the net, or the natural direCtion cof that 
admirable produétion of nature, at the place in which the 
inftrument is fituated, The obfervations of the dippi 
roperty of ama i 
more accurate initruments, and much greater attention, 
than thofe of the ieee deeiion of the compafs. 
r , the rver the magnetical dip- 
P made.a confiderable number of original obfervaticns 
with inftrumen uch capa uracy 3 and, in- 
deed, if the various circumftances which are capa 
great difficulty of the conftruction will be eafily perccived. 
The principal parts of a dipping-needle are an oblong piece 
of fteel called the needle, fo nicely poifed upon an horizon- - 
tal axis, as to remain in any fituation in which it may be 
placed when not magnetized: hence, when it is afterwards 
rendered pe aber it may place itfelf in that dire&tion 
which the magnetic virtue alone compels it to afflume. The 
inftrument mutt likewife be furnifhed with a divided circle, 
concentric with the needle’s axis ‘of motion, and fituated fo - 
f is very gre 
ica re d, the ‘ntroduion of dirt or du 
the axis and furtace upon which it refts, or ‘upon the needle 
itfelf,, will cafily derange the whole. It ts likewife difficult 
to make the obfervations free from error; 
angle of about 724° with the horizon, if the dipping-needle 
be fituated in a plane 20° diftant from the ma 
ridian, it will ftand nearly perpendicular to the 
for in this cafe the reedle, agreeably to the mechanical refo- - 
lution of forces, will place itlelf in the fituation which : 
ray 
as 
ble 
a. 
me 
rt) 
f=] 
: 
ct 
theo 
P> contemp porary 
— feem to give the dip much - eee than they 
h 
ought 
The neral mode of ee the dipping-needle, or - 
the fins ie confru@tion of the initrument, confilts of an 
oblong piece of flat fteel, ca'led the needle, broader in the : 
middle, s the extremities. An axis 
a through the middie of it, and its extremities move in 
o holes, fo- that the needle can move edgeways, upwards 
and downwards, like the beam of a pair of F {eales. Two 
lateral bars, in which the holes for the extremities of the 
axis are made, are earaae to a divided circle, which is to 
indicate the angle which the needle makes with the horizon. . 
The divided. circle, with the lateral bars and needle, = 
fixed . 
