1805. | 
-taken in furveying, will be fo much.the 
more correct. To the navigator and fur- 
veyor it will alfo prove the more accept- 
able, becaule they may vary their obfery 
vations from different parts of the arch, 
even when the diftance is from ninety to 
one hundred degrees. ‘ 
The divifions of the arches, and the 
nohius divifions, are executed with the 
utmott degree of precifion by the methods 
adopted, and the identical engine ufed, by 
the celebrated and much-regretted Ram{- 
den ; andthe telefcopes are of a defcrip- 
‘tion very fupericr to thofe formerly ufed 
for the beft fextants, having a much 
larger field of view, and by which objects 
willappear much more diftin¢tly than ufual. 
The foregoing are” the advantages of 
the new fextant, an infirument which, 
more than any other, will be found to 3 
cilitate, and determine to perfection, the. 
important problem of the longitude. The 
following cbfervations on the ‘compafs 
will fhew how much this valuable inftru- 
ment has likewife been improved. 
Tt is well known amongft mariners, 
that the compaffes generally ufed have 
been liable to many and great defecis ; 
that it feldom happens that the centre of 
motion and centre of gravity are to be 
found in the fame place; and that the 
card and needle have been fubje&t to a great 
deal of motion arifing from friétion, &c.— 
Nor are thefe and feveral other common, 
but very grofs, defects, confined to the 
common compaffes alone ; fince they will 
be found in all the beft azimuth and other 
compafies of the fuperior defcription.— 
An error in the conftruction of the centre- 
point, or pin, is°common to moft of 
them; as well as that, by the common 
mode of placing the gimbals, they are 
liable to a great deal of motion, arifing 
from that of the fhip, which is complete- 
ly avoided by the prefent mode of con- 
{truétion, 
The graduated ftop, or nonius, applied 
to Dr. Knight's and other azimuth com- 
pafles, for taking the bearings more pre- 
cilely, being placed vertically, is alfo the 
means, when uled, of pufhing the card off 
its centre, thereby injuring the centre- 
point, and reducing its utility: 
In the new compafs thefe defects are 
obviated, perhaps to the higheft degree 
of which the inftrument is fufceptible ; as 
this compats is fo formed, that the centre 
of motion and centre of gravity will al- 
ways be found in the fame point. The 
gimbals act upona peculiar and improved 
principle, which precludes the motion 
that would otherwife be communicated by 
_ Defcription of improved Nautical Inftruments, O11 
the rolling and pitching of the thip. By: 
the improper fituation of the weight in 
‘the kettle of the compafs, it is likewife 
commonly fubject to a great deal of mo- 
tion in a rough fea, which might be 
avoided, and is actually obviated in the 
new compafs, by its being fo differentl 
placed, that, however the inftiument a 
be agitated, it will preferve its accuftom- 
ed ftability.. An azimuth may therefore 
be taken with correctnefs, although the 
fhip’s motion be very confiderable. 
The card is fitted with an agate, and 
the point beneath is fo cenftructed and fo 
fhort, as to leave but very litle, if any, of 
that vibration to which the centre-point of 
the common, compafs is fubject. The 
needle is of a new form, fo fafhioned as 
never to deviate, when placed without the 
attractive atmofphere of iron, in the flight- 
eft degree from the real magnetic meri- 
diaa ; and it is fo tempered as ta retain 
its magnetifm for the longett period of time. 
The graduate circle is equally correé& 
with the divifions of the f{exiant; and the 
nonius, which is horizontal, upon a new 
original conttruétion, is very peculiarly 
fitted to give the correSt bearing with the 
utmott precifion, 
Added to all thefe, by another inven- 
tion, no fooner i8 an azimuth or bearing 
taken, than the card is, in an inftant, 
borne off the centre-point, and remains 
fixed, at the obferv-d bearing, for any 
time, at the pleafure of the obferver, uniik 
it again be fuffered to aét ; whereby, iike- 
wife, both the point and agate are effectu- 
ally preferved when out of ufe. 
An apparatus, or fun-dial, for fhewing 
the exact variation of the needle by infpece 
tion, whenever the fun is not ob{cured, is 
alfo occafionally fitted to the new compais. 
' T need not enlarge farther upon the ad-. 
vantages of the new in(truments. By the 
fextant, it is prefumed, that the longitude 
will be aftronomically afcertained with 
“greater accuracy then heretofore; and, 
by the compats, that the dead- reckoning 
will be much more. correét than ulual ; 
which mut be of efpecial com(equence in 
thick weather, or when obfervations tor 
the longitude cannot, from that or any 
other circumftance, be made. For the 
purpoles both of land and of maritime 
furveying, the advantages both of the fex- 
tant and the compalfs may be exper enced 
in the higheft degree. The accuracy of 
every furvey mult depend upon correét 
bafes ; and the direGlion of thefe baies, 
unlefs a true meridian line can be deter 
mined aftronomically, which is not al. 
ways convenient, and fometimes not prac- 
ticable, 
— 
SS 
