542 
ASTRONOMICAL OBSERVATIONS. 
N autical 
Almanack. 
Abbrevia¬ 
tions. 
Latitude. 
Meridian 
altitude. 
Reduction 
t o the meri- 
tlian, 
give much trouble to work out. It is officially adopted for H.M. skips, 
aud is tke text book of the Hydrographic Office. 
Tke Nautical Almanack. This can be bought for 2s., and is issued 
three years in advance. 
The following usual abbreviations are adopted ©, Sun ; U, SuiTs 
Upper Limb; £1, SuAs Lower Limb; A.T., Apparent Time; G.D., 
Greenwich Date; G.M.T., Greenwich Mean Time; Z.D., Zenith 
Distance; M.Z.D., Meridian Zenith Distance; R.A., Right Ascension; 
N.A., Nautical Almanack; D.R., Dead Reckoning— i.e. y reckoning by 
account. 
I.— Finding the Latitude. 
(a) By Meridian Altitude of the ©. 
This is a simple application of the rule that latitude is the sum of 
the Declination and Z.D. when both are N. or both S., and is their 
difference when they are of different names, or one N. and one S. 
j Example. —March 11th, 1881, observed the meridian altitude of T5 
in an artificial horizon 70° 34' 10", index error of sextant —3' 10", 
longitude 0° 7' 45" W., © bearing south. Required the Latitude:— 
o / // o / // 
Declination, p. i., N.A.... 3 32 6‘2 S Observed alt. in quicksilver ... 70 31 10 
Correction, tab. 19 Raper 0 0 0 Index error.. — 3 10 
Reduced declination . 3 32 6-2 S 2^70 31 0 
35 15 30 
Refraction, tab. 31 Raper. — 1 22 
35 14 8 
Semi diamr. tu, tab. 34 Raper... — 16 8 
34 58 0 
Parallax, tab. 34 Raper . + 7 
34 58 7 
90 00 0 
Z.D. 55 1 53 N. 
Declination ... 3 32 6 S. 
Latitude . 51 29 47 N . 
Finding the Latitude. 
(b) By Reduction to the Meridian . 
This observation may be taken either before noon or after noon, or 
some of the altitudes may be taken on each side of the meridian; in 
any case, the observations should not be taken at a greater interval 
than 25 minutes from noon, but the nearer to noon the better. It is 
usually called circum-meridional, because a set of the observations may 
be taken on either side of the meridian. It may be of especial value to 
officers abroad, as the altitudes can be taken without a chronometer or 
superior watch. 
A most valuable table (A) of reductions for Hour Angles in Time 
is here given ; it saves much labour in working out these observations, 
and is only to be found in very few books. 
