DIPPING. 
made wie | needles, conftru&ed 
Nairne for ao Board ns Lome ee ha reader will 
be enabled to judge of the accuracy which may be expefted 
from thefe obfervations, and of the pclae ich mult be 
attended 
L onl 
ew 
as 
es) 
to vibrate. nl 
minutes before the vibration ceafed. In fe experiment the 
rane aad confantly fhewed an angle of 72° 20’, with 
the ho 
Second te of pe eae with that fide of the infru- 
ment to the eaf, which was to the weft in the firft obferva- 
tions. The needle ae an mee of . 
42° 
Here the ends of the axis 
touched the agates. 
72 
“Third fet of experimentsy in ich poles of the needle 
-were reverfed, but the fame fide of the aa ae to the 
ealt, asin the fecond fet of aie and the needle ra- 
ther more magnetical, being touched with a free fet of 
magnets. In fix experiments the dip was conltantly 72° 
3 
Fo tae sae a ie oe viz. the fame fide of the in- 
ftrumen e eaft, a he firft fet of experiments. The 
dipping angle ek By the — with the horizon was 
Fifthly, the fame end vt ie needle being made north, as 
in the firlt fet of oo and aifo the fame fide of the 
the firt fet of experiments, 
8 72 igh 
refults of ie above el eae undoubtedly coin- 
cide — each other in a remar egree ; but fevera 
or with fimilar inftruments, have by no m 
with the fame remarkable coincidence ; and this i 
larly to be daria in the account of Mr. Hutchins’s obfer- 
vations on the dipping-needle, sade at Albany Fort, in 
1775; asis fated in the 66th vol. of the Phil. Tranf. page 179, 
where the eee a onthe very fame day, differ by 
aa degrees and up 
r. Daniel Bernoulli hus fhewn the method of conftru€- 
be done by a workman of the place, and palaneed with fome 
accuracy before impregnation, fo that y 
id 
Touch it (viz. magnetize it) and obferve the dit c 
its magnetilm, and then alter its balance in fuch a manner as 
to render it capable of arranging itfelf in the magnetical line, 
or in the dire€tion of the obferved dip, ee ae it be not pof- 
ed of magnetifm. Now touch it » giving it the 
re poles as before. It is plain that it will new approach 
exceedingly near to true ba becaufe its want of perfeA * 
equilibrium se i w degrees from the 
proper direétio nee eeu obfervation of the 
dip re eee fn from the firft, by the inaccu- 
a 
.T 
e have 
e ftructions of an inftrument, 
rate formation of - oe it will be proper to repeat 
the operation, w pat wil feldom be necef- 
fary. Mr. Bernoulli kee th le contrivance an{wer 
on purpofe of an univerfal hice ape in the fo 
ous manner. very lig ae afs graduated circle 
(Plate. Magnetifin, cree is fixed to one fide of the needle 
concentric with its axis, ae the whole is balanced as nicely as 
oar visas impregnation. A very light index C Disthen 
fitte e axis, fo as to turn rather {tify on it. This will dce 
ftroy ae equilibrium of the needle Jf the neec - has been 
made with perfect accuracy, and ddition 
of this index would caufe it alw ays to fettle a the index 
perpendicular to the horizon, a degree of the circle 
it may chance to point at. But as this is fcarcely to be ex- 
m the anes y 
‘yee dies is not deranged by the magnetifm from the pofition 
which gravity alone would give it. 
As we generally know 
fomething of the di 
again obferve the dip 
the index and this dip form a pair which is in the table. 
they do 
pair, we learn whether 
are : a {ame direction as before, or in the oppofite. 
e of this kind in the hands of an experienced phi-« 
lo oes was found to anfwer remarkably well. It is a con« 
trivance worthy of its ingenious author, and deferves to be 
recommended, becaufe it may be made for a moderate price, 
and of courfe it may afford the means of multiplying the ob- 
SS of the ie are of the utmoft confequence 
e theory of ma 
now deleribed ‘the beft and moft approved cons 
to which too much attention 
cannot be paid either 2 the artift who conftrudts it, or by 
the obferver who ufes it ; and we have pointed out the diffi- 
culties which muft be overcome, as well as the precantions 
ue h muft be attended to by both, hs moft - thefe ob- 
aw 
fe uniteadinefs of the fituation. 
the purpofe of rendering the dipping-needle e€ manapes 
le at {ca, was made by J. Lorimer, {crip- 
tion of it, which we fhell now fubjoin, is publifhed in the 65th 
volume of nil. Tra n this conitruétion the needle 
fhews, at the fame time and by itfelf, the horizontal and 
vertical dire& of magnet, more rl 
peaking, places itfklf in the magnetical line: whereas 
the dipping-needles, which we have de‘cribed in the pre- 
ceding pages, require to be fituated in the magnetic me- 
ridian. In fhort, this needle of D>. Lorimer anfwers at ance 
the purpofes of a dipping-needle, and of a common com- 
ee Fig. 30. is a oo of this dipping-needle. 
+ Whenever,”? Dr. r fays, “ any one m.ets with 
a terrella, or feria Toad fone, na firft thing he does 
o find out its poles; and having once difcovered 
den, he knows immedi dy how a fall bits of needle 
will 
