STANDARD - Survey Instrument Antique Center!

67
The adjustment of the polar axis to be truly at right angles to the line of sight of
the main telescope is made by two milled capstan-headed screws and two opposing
springs at right angles to each other below the base or leveling plate of the solar
attachment. As will be seen in making this adjustment it is not necessary to place
the solar telescope parallel or at right angles to the main telescope, but simply in the
same vertical plane of each set of leveling screws and springs at the time. This
adjustment is made by the manufacturer and thereafter needs only to be examined
at times.
If the adjustments are properly made the bubble of the level of the transit telescope
and those of the plate levels on the transit will all be in the center of their tubes, and the
vertical arc will read zero.
Bisect some convenient object, and turn the solar telescope sufficiently to the right
or left, around the polar axis, to make the image of the object traverse the field from
one side of the tube to the other. The image should remain bisected by the wire,
If not, loosen the four capstan-headed screws of the diaphragm till the above condition
is attained, and fasten the screws securely,
The solar telescope showing usually objects inverted, requires the cross-wire diaphragm
to be moved as described on page 58 of Manual.
Bisect any very distant object in the horizontal plane by the main telescope, and
clamp. Then, by means of the clamp and opposing tangent screws on the solar telescope,
bring its horizontal cross-wire to bisect the same object ; then, by means of the
capstan-headed screw of the solar telescope level bring the bubble to the middle of
its tube. This being done, the optical axes of the two telescopes will lie in parallel
planes for distant objects and the instrument is ready for use.
All these adjustments are made by the manufacturer, and need to be verified only
occasionally.
Before the solar attachment is available for finding meridian, the observer must
know his Latitude, and the sun's Declination for the day and hour of observation,
corrected for refraction, whence the
Reduction of Declination and Refraction,
The sun's Declination is given for noon of every day in the year, in the Washington
and Greenwich Ephemeris of the sun, for those meridians. The maps and charts
In use will give the difference of Longitude to all the precision required, and tables in
this manual give the required Refraction.
An example will best illustrate :
Required a declination table for the different hours of the day for April 25, 1885.
Lat. 44 N., and Longitude 97 W. At 15 to the hour, 97 of longitude is about
6 1 hours of time, and as this longitude is W., 12 o'clock, or noon, at Greenwich will
correspond to 5J^ A. M. at the place of the observer.
The declination, as given for that day, in the Greenwich Ephemeris, is 13 20'
04" N and is , shown to be gaining at the rate of 49" per hour (see column headed
Difference for one Hour, with the signs -f- for sun going North, and for SUB
going South).
If now, to the decimation for 5| A.M., we add the hourly rate of change successively,
we shall have the declination for the several hours of the day, observing that
the first increment is for only half an hour, thus :
Hourly difference Dec. -f- 49" j
Dec. 5 A. M. N. . . . 13 20' 04" +
Form of Daily Declination Table.
APRIL 25, 1885.
Hourly
:
1 p. M. N. .
difference + 49"
Dec. = 13 26' 11" +
" =13 27 00 -j-
" =13 27 49 +
" =13 28 38 +
" =13 29 27 +
" =13 30 16 +
" =13 31 05 +
6
7
...
...
13
13 13
13
20 28 -f
21 17 4-
22 06 +
22 55 +
2
3
4
5
10
11
M.
13
13
13
23 44 4-
24 33 +
25 22 4-
6
7
The above table must be corrected for the effects of refraction, before it is set off
on the vertical arc of the transit. Kefraction increases the apparent altitude of an
object, and thereby affects the declination of the object
tion when of the Afferent 1 name with the latitude.
the declina
^hn'shing [
-