STANDARD - Survey Instrument Antique Center!

84
c. Directions. For finding the Sun's apparent declination. Look in the table
of Solar
Washington Ephemeris against the date of the observation, and take out
the following quantities. First, the sun's apparent declination, with its sign, -jwhen
N., when S., from its column. Second, the hourly change, with its sign,
from its column. Find from a map or otherwise, the difference in longitude
between the place of observation and Washington, as near as one-half hour, or
seven and one-half degrees. This is -f- when W. and when E. of Washington.
Add to this difference of longitude the time of the observation from noon, this time
being -j- when the sun is W. and when E. of the meridian. Multiply the hourly
change by this result, in hours^ noting all the signs. Apply this product, regarding
its sign, to the sun's apparent declination as taken, from the table, for the sun's
apparent declination at the time of the observation.
d. Example. Date, 1881 6 14. Hour, 9h 26m 24*, A.M. Longitude
about 40 minutes East of Washington, considered in time.
O's apparent declination, 1881
Washington mean noon, -f 23 18'
Hourly motion,
6
15"
1"
14.
Time of observation from noon,
Longitude
2 hours 30 minutes, about.
East of Washington,
40 minutes.
Total time of correction,
/6 X 1" = 22^"
3 hours 10 minutes, = 3 l
/e hours.
Amount of correction = 3 l
O's apparent declination from table, -f- 23 18' .
O's apparent declination at time of observation, + 23 17' 53" nearly,
12. Reducing Observations.
a. Conditions. Let h' = the sun's altitude, as observed.
Let = the latitude of the place of observation.
Let 6 = the sun's apparent declination at the time of observation,
found as above directed.
Let z'= the sun's observed zenith distance.
Let z = the sun's true zenith distance, always -f.
used in the reductions.
Let k and A/ be two auxiliary angles
Let A = the azimuth of the line of sight of the instrument at the instant of the
observation, reckoned from the N. point of the horizon, either E. or W. as the sun
is E. or W. of the meridian.
Let t = the sun's apparent hour angle at the time of the observation, that is the
local apparent time from apparent noon plus the change in the sun's right ascension
between apparent noon and the time of the observation. This is -{- when W. and
when E. of the meridian, or -j- for P.M , and for A.M. times. The mean or
watch time is sufficient for use in 2.
Let p = an auxiliary angle used in some of the reductions.
Let all signs be faithfully regarded. Let logarithms be used.
b. Directions. For finding z from z' . Use the following equations.
*'=90 /?'
z = z' + 55" tan z'
C. Directions. For finding A when 0, 6 and z are given.
Find tan ^ (k fc') = cot ^ O~H) tan ^ O cot ^ z . (3)
When ^