STANDARD - Survey Instrument Antique Center!

55
Instead of using a plumb-line a simpler method having the advantage of not requiring
the instrument to be leveled up carefully is as follows: Set up the instrument
as near as may be convenient to a building, say about 20 feet, in order to get as high an
altitude as possible. Level up only approximately, clamp and bi-sect a point at the
base by the tangent screw. Then elevate the telescope and find a well-defined object
as high as possible, only using the telescope's horizontal axis. Now reverse telescope
and move instrument on its vertical center, again clamp, and bi-sect the point at the
base. If when the telescope is elevated it bi-sects the high object selected the adjustment
is correct. If it does not, proceed as described in the above method.
To adjust the level to the line of col Munition of the horizontal wire one
method is to use a sheet of water, or where that is not available, two stakes which are
driven with their surfaces in the same level plane.*
To make the adjustment with the stakes, level up the transit half way
between two points lying very nearly in a horizontal line, and say 300 feet apart.
Drive a stake at one of these points, place the rod on it and take a reading, first bringing
the bubble to the middle of its tube. Point the telescope in the opposite direction,
again bring the bubble to the middle of its tube, and drive a second stake at the second
point selected until the rod held upon the second stake gives the same reading as when
held upon the first stake. The tops of these two stakes now lie in the same level line.
Take up the transit and set it outside in line, as near as it can be focussed on the
first stake and level up. Now read the rod upon the first stake with the bubble in the
center and then upon the second. If the two readings agree, and the bubble is in the
middle of its tube, the adjustment is correct. If the two readings do not agree, then by
means of the telescope's tangent screw elevate or depress the telescope the amount required
until the horizontal wire reads the same on the distant rod. Next refocus
on the near rod, take a reading, then focus on the distant rod and see if the readings
are the same, if not, by means of the tangent screw again make the horizontal wire
read the same as on the near rod. Repeat this operation until both rods read
the same. Now with the horizontal wire bi-secting the distant reading make the adjustment
of the level by its capstan-headed nuts until the bubble is in the middle of its
tube when the level will be parallel to the line of collimation.
Another method of adjusting the attached level to the Transit Telescope
will be found on page 63.
To adjust the verniers of the vertical arc or full circle to read zero, in our
Engineer's Transit having the vernier between the legs of the standard. First level
up the instrument carefully so that the telescope's bubble will remain in the middle
of its tube when turned 180 in azimuth. Then set the zero of the vernier to read
within about % minute right with zero of the vertical arc. Then by the vertical
tangent screw place both zeros in coincidence and examine the 30' lines and if short
the vernier must be moved inwardly so that both of the end lines in the double vernier
will read right. If too long the vernier must be moved outwardly until this is
attained ; then fasten tightly. Now unloosen only just enough the screws that hold
the vertical arc or circle to the horizontal axis, to permit of "a slight shift, and then
with the bubble in the center slightly tap one of the spokes of the arc with the handle
of the screw-driver, until the zero of the vernier and that of the vertical arc are in
coincidence. This accomplished now fasten the vertical arc tightly to its flange.
Again level up the telescope as described above and see if the adjustment is correct; if
not, again slightly unloosen the vertical arc, tap it into position, repeat the same operation
over again until it is correct.
NOTE. If the vernier for the vertical arc is single, made to read both ways, in
reading it proceed to the right or left on the upper line of figures in the direction of
the graduation used, and if the coincident line of the vernier is beyond the 15' line,
continue on the lower line of figures on the other half of the vernier, so that the whole
graduation from 0' to 30' lies in the same direction. The verniers of our vertical arcs
are however, made mostly double as described on page 37.
The Adjustments of the Full Vertical Circle with Double Opposite
Verniers.
When the vertical circle in the Engineers' Transit is provided with a
vernier at eye-end or with double opposite verniers, the adjustment of the
vernier zero for normal position should be made by the two opposing capstan-headed
screws attached to the vernier frame at side of standard. Then to be lasting and
to avoid any strain upon the frame and lugs carrying these adjusting screws, proceed
as follows : First level up the instrument so that the bubble of the telescope
and plate levels remain in the center of their tubes when vernier plate is turned 180
in azimuth; then the zero of vernier "A," at eye-end, should be adjusted by the
*In general practice one will locate the stakes permanently at some convenient place near the