Line of Sight - Close Wyes

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Line of Sight - Close Wyes

A location to place transport is needed where well-described fixed spot can be readily found on opposite sides of it at a distance away as great as the telescope will show them clearly. It is well to have the marks at about the same angular distance, above on one side and below on the other, from the place chosen. The plate levels should be in adjustment, and the reversions of the transit made about the axis they are adjusted for.

Preparations

Putting up the transport smoothly in a convenient location. Level it carefully. Set the line of sight on a distant, well-defined, fixed mark. Reverse the telescope about the transit axis and find a similar mark in apparent line. Rotate the telescope back and see if the line of sight strikes the first spot. Do it again these pointing's, making the necessary corrections in the setting and levelling of the transit till the line of sight will surely strike the first mark again when the telescope is turned back.

Test

Let it go the mandatory clamps and rotate the telescope about both axes. Equal the transport if the levels show a slight disturbance. Set the line of sight on the first mark. Reverse the telescope about the transit axis and see if the second mark is in apparent line. Rotate the telescope back to the first spot, as before, and, by the same means, spot sure the line of sight will strike the spot. Then reverse the telescope, as at first, and note the deviation of the line of sight from the second mark.

Correct

By estimation, one-fourth of the deviation of the vertical cross wire by means of the screws at right angles with it that hold the cross wires in the telescope tube. Whether the telescope shows objects right side up, or not, turn these screws as if to increase the apparent deviation. Loosen the screw permitting the desired movement before turning the other. Leave the screws under a gentle, even, strain. If the deviation is large, loosen the other pair of screws slightly, but have a care not to get the vertical cross wire inclined. Set the line of sight again upon the first mark, as at first. Repeat the tests, corrections, and tests till no deviation appears when the test is made.

This adjustment is required theoretically in reading angles, but not in running straight lines. It conforms to the best working conditions, however, both optically, and in the field practice.

What's the difference between plain and geodetic surveying?