210 
the manner of a real narrative than a 
feigned ftory. 
Where England, ftretch’d towards the fetting 
fun, 
Narrow and long, o’erlooks the weftern 
wave, 
Dwelt young Mifagathus. 
If this hint thould Jead to the difcovery 
of the fuppoted faét, I fhall rejoice at my 
having thrown it out. 
Chejier, Feb. 4, 1805. A. B. 
To the Editor of the Monthly Magazine. 
SIR, 
LTHOUGH the Monthly Maga- 
zine has not hitherto been particu- 
Jariy diftinguifhed for communications 
which more peculiarly relate to improve- 
ments in nautical fcience, yet, as I am 
perfuaded that many of your readers, in 
the widely diffufed extent of its circulation, 
will not be difpleafed with fuch communi- 
cations, permit me to requeit your infer- 
tion of the following brief defcription of 
a newly-invented fextant, for taking celef- 
tial ob{ervations, and of ‘baie eflential im- 
provements which have been recently 
made in the conftru&tion of the mariner’s 
compa{s, particularly of the azimuth- 
ccompafs, which is made ufe of in deter- 
mining the variation of the magnetic- 
needle at fea. It would be fuperfluous fer 
me to attempt a defcription of the great 
importance of thefe inftruments to the na- 
vigator. It would be equally fo to de- 
icribe the numérous defects to which they 
are fubjeét, and the conliderable errors in 
determining a fhip’s place, which are 
fometimes experienced by the moft expert 
and {cientific obiervers, in confequence of 
unknown errors of the fextant, as well as 
of thofe which are found in the reckoning: 
in confequence of defe&ts in the compafs. 
The methods of determining the longi- 
tude, the effet of the genius and Jabcurs 
of a number of diiinguifhed men, parti 
calarly of our own country, have been 
carried toa wondertul degree of accuracy 5 
and the precepts which have been detail- 
ed, with fomuch judgment, fcience, and 
clearnefs, have been, in innumerable in- 
flances, carried into praétice by careful 
obfervers, with initruments which had 
been improved by the mechanical fkill of 
a Ramfden. But, althoughthe accuracy 
of the precept, the attention of. the ob- 
ferver,. and the ingenuity of the artift, 
have frequently been fo combined as to 
promi: fe the utmoft preeifion in the deter- 
niination, ani to fix a re‘ult which fhould 
be conlidered as a itandard, fubfequent ob-= 
~ feryations, made with equal eare, by the 
Defeription of improved Nautical Inftruments. 
[April 1, 
fame precepts, and even with the fame in- 
ftruments, have feldom been found to cor 
refpond therewith ; while there have exift- 
ea no means of afcertaining the truth or = 
falfehood of any individual obfervation. 
There is not the leaft reafon to doubt 
that thelfe differences, which are generally 
very confiderable, arife chiefly from the 
imperfection of the inftruments in general 
ufe ; and although means have been 
pointed out for reducing fuch “inaccura- 
racies, it does not appear that they have. 
ever approached to perfection. 
The new fextant, which, from its 
figures may be called a double fextant 
(and as it anfwers the purpofe for which 
two fextants are generelly taken to fea), 
is extremely fimple in its conftruction ; 
and its fize and weight are but very little 
greater than of thofe in common ufe. Its 
formation differs from the latter in its 
having two graduated arches and two in- 
dexes, by which it poflefles the peculiar 
properties of always exhibiting the index- 
error (the moft common error of the fex- 
tant), if any, the refults of which will of © 
courfe be obviated; and fhould it happen 
that there exifts, from any caufe whatever, 
that is to fay, from the contraétion orex- 
panfion of the metal, by cold or héat, in- 
varying climates, &c. the leaft ‘degree of 
error, it may, at al] times, be exaétly 
determined and allowed for ; fo that, in 
no cafe,-can any error, in a determina- 
nation of latitude or ef longitude, arife 
from this caufe. For, in taking an ob- 
fervation, the two indexes may be moved, 
almoft at the fame inftant, in oppofite di- 
rections, fo as precilely to correct each 
ather. 
Another pectBt advantage is, that’ of 
allowing a fecond obfervation to be taken. 
without P thifting the inftrament from the 
eye ; becaufe, no fooner fhall an obferva- 
tion be taken by means of one arch, than, 
the index being clamped, a fecond obfer- 
vation may be inftantly taken- with the 
other arch, and equally correét. Thele 
are fingular conveniencies, efpecially as it 
frequently happens, that, after taking am 
obfervation, before the angle on the arch 
can be read off, and the infirument ad- 
jufted for a fecond obfervation, the object 
becomes obicured. Obfervations are there- 
fore made by the new inftrument with a 
faving of time and trouble, and with 
greater accuracy than heretofore. 
Hence it will appear, that the principal 
errors of the (extant hitherto in general 
ufe, are obviated ; 
determinations of latitude and longitude 
by celeflial obfeyvation, and the angles 
taken 
that, confequently, — 
» . 
ne 
i oe 
