STANDARD - Survey Instrument Antique Center!

(5.) Astronomical Triangle. The height of the sun is measured in a plane passing
through the " Vertical " and the sun, and is called his Altitude, whence his distance
from the " Vertical " is his Co-Altitude.
In the same manner, the distance from the sun to the "Pole," is his co-declination;
and the distance from the ." Vertical " to the pole, is the observer's Co-
Latitude. These three compliments form what is called the Astronomical Triangle.
Thus we have the three sides of a spherical triangle, from which to find the
several angles.
(6.) The angle at the Pole, contained between the meridian of the observer and
that passing through the sun, is called the Hour Angle, as it gives the distance from
the sun to the observer's meridian, in time or arc, and is usually represented by the
letter H.
(7.) The angle at the "Vertical," or at the observer's zenith, contained between
the meridian and a vertical plane passing through the sun, is called the Azimuth
Angle, and is usually represented bv the letter Z.
This angle is the one particularly important to surveyors, as from it the place of
the meridian is readily determined.
Navigator's look for this angle every day, when an observation can be had, and
solve the triangle for Z, by one or both of the following equations.
in which
cosS cos(S p)\| ...... (a.)
(b.)
.
' v >
L = Latitude. Z = the required Azimuth
d = Declination. p = Polar Distance = 90 d.
h = Height of the sun's center, corrected for refraction and parallax.
NOTB. The correction for parallax, which is
usually about 6". and never exceeds 9", may be neglected
xcept in work of great precision.
To solve these equations numerically requires much computation, but the Solar
Transit solves them for Z, mechanically, with no more computation than that required
to deduce the declination for the longitude and local time of the observer, from that
given in the Nautical Almanac for the day.
From the above definitions, it is readily seen that the following conditions, or
relation between the parts of the instrument, must be established.
(A.) The polar axis must be Vertical, when the vertical arc (latitude arc) reads
zero, and, consequently, perpendicular to the cross axis of the transit telescope.
(B.) The horizontal cross-wire of the solar telescope must be parallel with the
plane of its rotation around the polar axis; i.e. it must be parallel with the plane
of the equator.
(C.~) The plane passing through the vertical wire and the optical axis of the
solar telescope must be at right angles to the cross axis of the solar telescope.
(D.) The bubble of the level-tube on the solar telescope must be in the middle
of its tube, when the optical axis of that telescope is in the plane of the horizon.
These conditions are obtained by the following
Adjustments.
Having attached tL? ' Solar" to the cross axis of the telescope, as directed under
the head of "Remarks," and having leveled up the transit (supposed to be in perfect
adjustment) carefully, set the vertical or latitude arc to zero, observing that, upon
rotating the whole instrument 180 in azimuth, the bubble of the level of the transit
telescope is in the middle of the tube. Bring the level bubble of the solar telescope to
the middle of the tube by means of the clamp and opposing tangent screws of the
axis 180 to see if its
solar telescope then revolve the solar ; telescope on its polar
bubble remains in the center of its tube :
if not, remove half its error by means of the
opposing tangent screws, the other half by the milled capstan-headed screws below
the base-plate, until it remains in the center of the tube. Repeat if necessary.
Turn the solar telescope 90 on its polar axis, and by the milled capstan-headed
screw level the base-plate and bring the bubble to the center of the tube. Repeat
the operation until the bubble of the solar telescope remains in the center of the tube
upon revolving the solar telescope around its polar axis. (This condition must be
attained before the polar axis can be set to the co-latitude of the observer and ; being
.attained it needs no further attention than being examined at times for verification).