888 % COM 
on 3, the fight vane ; 4, a lpagnifjing glafs, which is alfio 
moveable on the other vane; 5, the nonius.or vernier; 
6, a Aide for moving the vernier fo as to ftop the card in 
taking the azimuth ; 7, a double convex glafs, by which 
the di'vifions on the vernier may be read with accuracy. 
Fig. 8. is a feftion reprefenting another application of the 
magnetic needle and card, conltrufted by Mr. M'CuIloch: 
aa, the common wood box ; ' bb, the brafs compafs box ; 
cc, the brafs fupport for the circle and pendulum; d, the 
pendulum; e, the agate; ff, the magnetic needle and 
card; gg, the brafs circle; hk, the glafs cover and brafs 
ring; i, the lead weight. 
But, according to the obfervations of Mr, Bernard Ro¬ 
mans, of uPenfacola, neither of thefe companies are to be 
fully relied on in a hollow or high lea. This he fays is 
owing to the box being confined to only two motions, 
both vertical and right angles with each other; by 
which confinement of the box, upon any fucculfion, more 
efpecially Hidden' ones, the card is always put into too 
much agitation, and, before it can well recover itfelf, 
another jerk prevents its pointing to the pole ; nor is it 
an extraordinary thing to lee the card unfhipped by the 
violence of the Ihip’s pitching. Thefe inconveniences', 
he fays, are to be remedied to the full, by giving the box 
a vertical motion at ever}' degree and minute of the circle, 
and compounding thefe motions with a horizontal one of 
the box as well as of the card. By this unconfined dif- 
pofition of the box, the effefts of the jerks on the card 
are avoided, and it wiil always very lteadiiy point to the 
pole. He informs us, in the Repertory, vol. iv. that he 
fiaw a compafs of this kind, made in Holland, that under¬ 
went all the lliocks and agitations of a hard gale, which 
lafted fome days, and during which'there was no other 
compafs of the fmalleft fervice, Nicholfon, however, feems 
to think that the compafs is very little dilturbed by tilt¬ 
ing the box on one fide, but very much by fudden hori¬ 
zontal changes of place ; that a fcientific provifion againft 
the latter is therefore the chief requ-ilite to be attended 
to. He is likewifc of opinion, that it would greatly im¬ 
prove the compafs to make the needle flat and thin, and 
to fufpend it, not, as is commonly done, with its flat fide, 
but with its edge uppermoft; for it being a well-known 
fa ft, that foft Iteel lofes its magnetifm looner than hard, 
at is obvious, that unlefs both fides of a needle be equably 
hard (which is almoft impoflible if they be diftant from 
each other), the magnetic power will, in-'procefs of time, 
deviate towards the harder fide.- 
The ufe of 1 the azimuth compafs is to take tire bearing 
of any celeftial objeft, when it is in or above the hori¬ 
zon,, that from the magnetical azimuth or amplitude, the 
•variation of the needle may be detefted and known. As 
there are thirty-two whole points quite.around the circle, 
which contains 36-0 degrees, therefore each point of the 
compafs contains the thirty-fecond part of 360, that is, 
i if degrees, or n° 15'; confequently the half point is 
37* 30", and the quarter point 2 0 48' 45'-'. 'Thefe points 
of the compafs are otherwife called rhumbs. 
The Chinese compass. 
We are informed, by fir George Staunton, that the 
compafs, among the Chinefe, is in univerfal ufe. With 
them the magnetic needle is feldom made to exceed an 
inch in length, and is lefs than a line in thicknefs. It 
is poi!ed with great nicety, and is remarkably lenfible ; 
by which is meant, that it appears to move at the leaft 
change of pofition, towards the ealt or weft, of the box in 
which it k fufpended ; though, in factj the nature of the 
magnet, and the perfeftion of the machine containing it, 
confiit in the needle’s privation of all motion, or its con¬ 
tinuing to point always lteadiiy towards the fame portion 
of the heavens, however rapidly may be whirled the com- 
pafs-box, or other objefts turrounding it. This lteadi- 
nefs, in the Chinefe compafs, is accomplifhed by a parti¬ 
cular contrivance, as,defcribed by Mr. Barrow, the altro- 
nomical and mathematical attendant on the etui of Ma- 
PASS. 
cartney, in his embafly to China. ’ “ A piece of thin 
copper is (trapped round the centre of the needle. This 
copper is riveted by its edges to the upper part of a final! 
liemifpherical cup, of the fame metal, turned downwards. 
The cup, fo inverted, ierves as a focket to receive a Iteel 
pivot rifing from a cavity made into a round piece of 
light cork, which thus forms the compafs-box. The fur- 
faces of the focket and pivot, intended to meet each 
other, are perfeftly polifhed, to.avoid, as much as poiii- 
ble, all friftion. The cup has a proportionably broad 
margin, which, befide adding to its weight, tends from 
its horizontal pofition to keep the centre of gravity, in all 
fituations of the compafs, nearly in co-incidence with the 
centre of fufpenlion. The cavity, in which the needle is 
thus fufpended, is ini form circular, and is little more' 
than fumciefit to receive the needle, cup, and pivot. 
Over this cavity is placed a thin piece of tranfparent talc,' 
which prevents the needle from being aftefted by any 
motion of the external air ; but permits the apparent mo¬ 
tion of the former to be ,eafi 1 y obferved. The fmall and 
fliort needle of the Chinefe has a material advantage over 
thofe of the ufual fize in Europe, w ith regard, to the in¬ 
clination or dip towards the horizon ; which, in the iat-. 
ter, requires that one extremity of the needle fliould be 
made fo much heavier than the other, as will counteraif 
the magnetic attraction. This being different in different 
parts of the world, the needle can only be accurately 
true at the place for which it had been, conftrufted. But 
in fliort and light needles, fufpended after the Chinefe 
manner; the weight, below the point of fufpenlion, is 
more than fufficient to overcome the magnetic power of. 
the dip or inclination, in all fituations of the globe; and 
therefore fuch needles will never deviate from their ho¬ 
rizontal pofition.”—"The circumltance of ftrapping or 
aiming the needle with copper, appeals to be the very 
improvement fuggefted by captain O'Brien Dudley, in 
the firft volume of the Repertory of Arts ; hut lie recom.- 
niends foft iron for this purpofe.. 
Upon the upper furface of.the.box are drawp, as reprer 
fented in the engraving, fig. 9. feveral concentric lines or 
circles, according to the various lizes of the compals-box. 
This is feldom lefs than four inches in diameter. The 
circles are diftinguifhed by different Chinefe charafters. 
Eight are marked on the firft or innermoft circle; four 
of which denote the cardinal points of ealt, weft, north, 
and fouth ; and four the bifefting intermediate points. 
The lame eight-charafters alio, fignify eight equal fubdi- 
vilions of the natural day, or fpace during which the 
earth revolves upon its own axis in purfuing its courfe 
round the fun, every fubdivifion being of three hours. 
The charafters denoting each of thefe are fo'placed as to 
point out nearly the pofition of the fun at thole different 
portions of the day, beginning at funrife, of which the 
character means alio the eaftern portion of the heavens. 
With this firft circle of eight diviiions agrees the firft 
■compafs, as ftated above, which is faid to have appeared 
in Europe in the beginning of the fourteenth' century ; 
and which, by fubfequent fubdivifions, was improved in¬ 
to thirty-two points, as lea men became more expert and 
accurate in obfervation. In another circle of the. Chinefe 
compafs are twenty-four divifions, in each of which a 
charafter is inferred, which marks at the lame time, a 
tw r enty-fourth portion of the heavens, and a twenty-fourth 
part of the natural day. According to this divifion, each 
point, or twenty-fourth portion of the compafs, compre,- 
hends an integral number of fifteen degrees out of three 
hundred and fixty, into which all circles 1 of the celeitial 
fphere have been agreed to be divided, probably iince that 
early period when the number of days, in which the fun 
'performed his apparent courle, was, fuppofed to be three 
hundred and fixty. The remaining circles round the 
Chinefe compafs contain the charafters of the cycle of 
fixty years, by which this nation regulates its chrono¬ 
logy, and other charafters exprelfive of their phiiqfophi- 
cal and mythological doftrines, to which they are fo 
