546 
ASTRONOMICAL OBSERVATIONS. 
Star-chrono¬ 
meter. 
his watch on Gr.M.T., and with its daily rate. This is shown in the 
example :—1881, March 10th, A.M. at place, the following observations 
were taken to find Apparent Time at place, and thence the Longitude ; 
the error of the watch, Feb. 25th, was 10 seconds fast, and its rate was 
1 second losing daily. 
Longitude by Altitude oe the Sun. 
Month. Day. Times by watch. 
h. m. sec. 
March 10 th . 
10 
19 
33 
10 
20 
12 
10 
20 
51 
8 ) 
31 
00 
36 
Mean . 
10 
20 
12 
Error . — 
10 
10 
20 
2 
Acctd. rate. + 
13 
G-.D. March9th... 
22 
20 
15 
f When great exactness is 
required, note thermometer and 
barometer, and correct refrac¬ 
tion by tables 32 and 33 of 
Eaper, or by any similar table. 
Altitude .. 
Latitude.. 
Polar dist. 
Latitude, 51° 31' 00". 
£l’s alt. in quicksilver. 
O / 
58 
55 
00 
59 
00 
30 
59 
8 
00 
3 )l77 
3 
30 
Mean . 
.... 59 
1 
10 
Index error. 
. — 
3 
10 
2 )58 
58 
00 
Reduced alt. .. 
.... 29 
29 
00 
f Refraction .. 
• — 
1 
43 
29 
27 
17 
Semi diameter. 
.. + 
16 
8 
29 
43 
25 
Parallax. 
. + 
7 
True altitude .. 
.... 29 
43 
32 
O. . . . . /./ / 
29 43 32 
51 31 00 Sec. .. 
93 57 31 Cosec. 
Original error of watch 10 secs, 
fast. 
Daily rate ... 
... 1 
sec. 
losing. 
Interval . 
s. 
Accumulated rate 13 
O 
t 
// 
Declination, 
(p.ii.N.A.)j 
| 4 
19 
19 S. 
Hourly diff. .. 
21 
48 
Red. decl. 
3 
57 
31 
Eq. time (p. "i 
ii. N.A. ... J 
> h - 
' 9 
m. 
10 
secs. 
37-45 
Hourly diff. 
— 
15 
Red. eq. time.. 
10 
22 
O 
/ 
Declination. 
.. 3 
57 
31 S 
90 
00 
00 
Polar dist. 
. 93 
57 
31 
0-206009 
0-001037 
Sum.. 2 ^ 175 
12 
3 
| sum. 87 
36 
1 
Cosin. 
8-621962 
Diff. between alt. and £ sum 57 
52 
29 
Sin. 
9-927827 
Log. sin. square... 
8-756835 
Hour /_ 
If the sights are A.M. subtract the 
hour Z from 24 hours, and the re¬ 
mainder is app. time at place, reckoned 
from the preceding day. 
li. 
m. 
sec. 
1 
50 
38 
The best time to take 
24 
0 
0 
sights is when the sun 
is about four hours from 
22 
9 
22 
the meridian. 
10 
22 
= Eq. time. 
22 
19 
44 
Mean time at place. 
22 
20 
15 
Gr.M.T. 
31 Longitude in time 0° 7' 45" W. 
Finding the Longitude. 
(h) Finding A.T. at place by Altitude of a Star or Planet, and thence 
the Longitude by chronometer . 
The following example is that of a planet , Venus, in which the 
Declination and R.A. have to be corrected for G.M.T., and parallax has 
to be applied to obtain the True Altitude. 
When a star is observed no correction is required for R.A. or 
declination, and stars have no parallax. 
