544 
ASTRONOMICAL OBSERVATIONS. 
'Example .—March 10th, 1881, in a place whose estimated latitude was 
51° 28' N., longitude 0° 7' 45" *W., took the following observations 
and times to determine the latitude. Error of watch on Gr.M.T., Feb. 
25th, was 10 secs, slow, and its rate was 1 sec. losing. Its error on 
A.T. was 10' 25" fast. Index error of sextant —3' 10". Find the 
latitude. 
Latitude 51° 28' N. by account, © bearing south. 
Month. Day. h. m. sec. 
Noon © on meridian. 00 00 00 
Long. 0 7 45 in time, 1881, Mar. 10 + 31 
(tab. 17 Eaper) -- 
G.D. of transit (apparent 
time). Mar. 10 ... 31 
h. m. sec. 
Mean of the times by watch. 11 58 17 
Error of watch for Gr.M.T. + 3 
G.D. corresponding to the 
mean of the observations, Mar. 9 ... 23 58 20 
Month. Day. ° ' " 
Decln. at mean noon (p.ii.N.A.) Mar.10... 3 55 49 
Corr. by hourly diff. N.A. + 1 
Corr. Eq. T. to apparent time 10 22 Decln. at mean of the times. 3 55 50 
To find what time the Watch will show at Noon. ~) 
h. m. sec. | 
Time of noon . 12 00 00 !_ 
f Error of watch on apparent time... 0 10 25 | 
Time the watch will show at noon = 12 10 25 J 
f The error of watch on A.T. should be Take the difference between the time the watch 
found by a sight, in the usual way, and can will show at noon and each of the times shown 
be found from the Hour / of the sights used by the Avatch when the altitudes were, and the 
for finding Longitudes by chronometer. differences will be the Hour Angles. 
Lat. D.D. 51 28 0 Cos. 9*794467 
Decl. 3 55 50 Cos. 9*998977 
M.Z.D. ... 55 23 50 Cosec.0*084572 
N. ... 289*6 Log. 2*461799 
In " 218*7 Log. 2*339815 
Deduction ... 3 18*7 
O / // 
Observed altitude si 68 34 46 
Index error — 0 3 10 
If taken in Quick- J 2 ) 68 31 36 
silver, divide by ) /_ 
34 15 48 
Defraction . — 125 
13 14 23 
Semidiameter...... + 16 8 
34 20 31 
Parallax. + 6 *5 
34 30 37*5 
Deduction. 3 38*7 
Meridian altitudes ... 34 34 16*2 
90 00 00 
Meridian zenith dist. 55 25 23'8N. 
Declination . 3 55 50 S. 
Mean ... 289*6 = N. (above) r Latitude . 51 29 33*8N. 
h. 
Watch shows 
m. sec. 
at noon. 
Watch 
Hour 
Nos. table 
A 
©’s mer. zenith dist. 
times. 
angles. 
il 
above. 
nearly. 
h. m. s. 
11 57 9 
o / // 
0 13 16 
345 
O / // 
Decl. noon 3 55 50 
Lat.(D.D-) 51 28 0 
11 58 19 
0 12 6 
287 
Mer. Z.D. 55 23 50 
11 59 25 
0 11 0 
237 
N.B.—The merid¬ 
ian zenith distance is 
equal to the sum of 
the latitude and dec¬ 
lination when they 
are contrary names; 
or their difference 
when of the same 
names. 
3 ) 869 
Times by watch. 
Alt. art. horizon. 
h. m. sec. 
O / // 
11 57 9 
68 33 40 
11 58 19 
68 35 00 
11 59 25 • 
68 35 40 
) 35 54 53 3' 
) 205 44 20 
Mean 11 58 17 Mean 68 34 46 
m. s. 
Equation of time (p.i. N.A.)... 10 22 
Corr. by hourly diff. N.A. 0 0 
