633 
NAVIGATION. 
being too flow for mean Greenwich time nirn.pf. Re¬ 
quired the longitude. 
H. M. S. H. M. S. 
Apparent time 4 3 6P.M. Timeper watch 2 o o 
Equat.of time—o 3 56 Watch error -j-o 11 9 
Meantime 3 59 10P.M. Ti.atGreenw. 2 n 9P.M. 
Ti. atGreenw. 2 11 9 
It. M. 
T m. alt. 10 01 Log. in col. of fifing is “ 3-53071—100 Tr.T. 
Zen. dill:. 59 59 N. Log fee. mer. alt +3 In.5 06247 
The S. being on the equator - 
8-59318 
Subtraft log. ratio 0-30103 
Log. fine chan, of alt. i° 08' 8-29215 
Diff. of time 1 48 1 equal to 27 0 o'15" eaft longitude. 
To fin'd the Latitude by one Altitude of the Sun, when 
the Time is not more dijlant than one Hour from Noon. 
I. To find the true Time. 
When the fun’s declination and complement of the 
latitude are both north or both fouth, their fum, but, if 
one be north and the other fouth, their difference, is the 
meridian altitude. 
From the natural fine of the fun’s meridian altitude, 
fubtraCt the natural fine of the obferved altitude. Then 
add together, 
The log. co-fecant of the comp, of the lat.l reject their 
The log. fecant of the fun’s declination, J indices, 
And the common logarithm of the difference of natural 
fines, intoonefum. The fum of thefe three logarithms being 
'found in the column of riling, the hours, minutes, and 
fecohds, correfponding to it, will be the true time from 
noon when the altitude was taken. 
Ex. 1. Being at 1 'ea in latitude 50 0 4'N. by account, 
when the fun’s declination was 20 0 fouth, at iih. 17m. 
A. M. per watch, fun’s alt. was i9°4o'. Required the 
'true time'. 
Comp.lat.39 56 N. Co-fec.0-19254 
Teclina. 20 00 S. Sec. 0-02701 
'Sup.m.alt.19 56 N.fine 34093 
.- L. ra. 0-21955 
•‘ebfer.alt.19 40 N.fine 33655 
438 Com.L. 2-64147 h. m. s. 
—-- --- 12 00 00 
Log. in col. of riling 2-86102 is =00 27 38 
True time at fea 11 32 22 
II. Having the true time previous to the obfervation, 
to find the change of altitude. 
Add together the logarithm found in the col. of rifing-, 
anfwering to the minutes and feconds the fun had to rife 
when the altitude was taken, and the feCant of the fup- 
pofed meridian altitude : from this fum (the index being 
increafed by 5) fubtraCt the log. ratio, the remainder is 
the log. fine of the change of altitude from the time of 
obfervation to noon ; which, being added to the obferved 
altitude, gives the fun’s meridian altitude. 
Loo-, in col. ofrifing of 27m. 38f. 2 86102 Obfer.alt. 19-40 
Log.fee.m. alt. 19 0 56'4-5 Index 5-02683 Cha.ofalt.+ 16 
7 88785 Tr.m.-alt. 19-56 
Subtract log. ratio - 0 21955 -- 
Log. fine chan, of alt. 16 min. 7-66830 
Ex. 2. Being at fea in lat. 6o° N. by account, when 
the fun was on the equator, at ih. om. P. M. per watch, 
the fun’s alt. was 28° 53'. Required the true time, and 
latitude. 
Com.lat. ) 3o°oo'N. Nat. fine 50000 C. fee. 0.30103 Log. ratio. 
Mer. alt. $- 
Ob. alt. 28 53 ~Nat. fine 48303 
Ch. of alt. 1 08 1697 Co.log. 3-2296* 
Ex. 3. Being at fea in lat. 39 0 28' N. by account, fun’s 
declination 20 0 41' N. at 26m. 28ft P. M. fun’s alt. was 
71 0 1 o'. Required the true time, and latitude at the 
fhip. 
Comp. lat. 50-32 N, 
Declination 20-41 N. 
- Co. fee, o-r 1239 
Sup.m, alt. 71-13 Nat. fine 94674 Secant 0 02893 
Obfer.alt. 71-10 Nat. fine 94646 L. ratio 0-14132 
Chan. alt. 3 ———- 
-. 28 Com.log. 1-44716 
T. mer. alt. 7113 
Zen. dift. 18-47 S. 
Declination 20-41 N. 
Lat. in 39-28 
■ ■ ■ — ■ ■ M. S. 
Log. In col. of rifing is ~ 1-58848—6 30T.T. 
Log. fee. fup.mer. alt. + 5-49216 [at ft. 
7 08064 
Subtract log. ratio 0-14132 
L. fine chan, of alt. 3 in. 6 93932 
The altitudes for determining how much the watch 
differs from apparent time had better be taken in the 
morning, or evening, when the fun’s altitude does not 
exceed 18 degrees. 
An error in the fuppofed latitude can make very fmall 
difference in the change of altitude ; and the nearer the 
altitude is taken to noon, the better to find the change of 
altitude. 
This method is not to be depended on fliould the appa¬ 
rent time exceed an hour from noon, and, in fome in- 
ftances, not then; fuch as, altitudes taken near the equa¬ 
tor, or when the meridian altitude exceeds 60 degrees ; 
nor is there much occafion for this method, or that of the 
double altitudes, there, fince there is generally a clear ho¬ 
rizon, and, confequently, a meridian altitude is eafily 
obtained. 
To find the Latitude by the Meridian Altitmde of the Moon. 
To the longitude of the given place in time add the 
number from Tab. XVI. Moore, correfponding to that 
longitude, and the daily variation of the moon’s paflage 
over the meridian on the given day (Nautical Almanac, 
p. vi.), if the longitude be weft; but fubtraCt the fum if 
the longitude be eaft : the fum or difference will be the 
time at Greenwich when the moon was on the meridian 
of the given place. 
In page 7th of the month in the Nautical Almanac, 
find the moon’s femi-diameter, and horizontal parallax, 
at the neareft noon, or midnight, to the reduced time, 
which will be fufficiently accurate for the purpofe of 
finding the latitude. 
Take the difference between the moon’s femi-diameter 
and dip, and add it to the obferved altitude, if the lower 
limb was obferved, but fubtraCt their fum if the upper 
limb was obferved; the fum or difference will be the ap¬ 
parent altitude of her centre. 
From the proportional logarithm of the moon’s hori¬ 
zontal parallax, increafing its index by 10, fubtraCt the 
log. co-fine of the moon’s apparent alt. the remainder 
will be the prop’, log. of the moon’s parallax in altitude, 
from which take her refraction. The difference will be a 
correction, which, being added to the apparent altitude, 
will give the true altitude of her centre: hence the zenith- 
diltance, to which apply her declination, and you will 
have the latitude, 
7V 
VGirXVI. NO. II4I. 
The 
