Surveying by Thomas William Norman

Author:Thomas, William Norman
Language: eng
Format: epub
Tags: Surveying
Publisher: London, E. Arnold
Published: 1920-03-25T05:00:00+00:00

Mi

required, 0 is sighted from B, and £ ^

the graduated wheel rotated until the ' ^iq. 184.

points A or M are seen by reflection to

coincide with 0. The range is indicated by the reading as before.

If desired, the range may be determined by setting out M at right angles to AO from A, viewing 0 by reflection as already explained, then fixing the scale at the 1000 reading and finding by trial a point

B on MA produced, at which the image of 0 coincides with M. The distance AO is then 50 x AB.

Or if the point 0 is sighted directly from A, then at B the image of M is made to coincide with 0 as seen by direct vision, and AO = 50 AB as before.

Adjnstment of the Telemeter.—A point M is accurately set out by any of the usual methods (e.g. box sextant, theodolite, etc.), so that AM is at right angles to AO.

The zero of the graduated collar is brought into coincidence with the fixed mark on the tube, and the arrow mark on the collar of the small toothed wheel is made to coincide with the fixed arrow on the front of the instrument.

The operator then stands directly over A, steadies the instrument against a ranging rod if he wishes, and directs the telescope to 0, when the image of M should coincide with 0 on the horizon glass. If not, the instrument requires to be adjusted.

To complete the adjustment, if it is found necessary, the small toothed wheel is rotated until coincidence is obtained between M and 0, when the mirrors shoidd be inclined at 45"^, the scale still reading zero. The arrow mark on the collar of the toothed wheel is thus moved relatively to the fixed arrow, and it is required to bring it back into coincidence without altering the relative positions of the mirrors. Consequently, the toothed wheel itself must not be disturbed, but by loosening a small set screw, the collar upon which is engraved the arrow mark may be rotated relatively to the wheel untU the two arrows again coincide; the set screw is then tightened and the collar secured in position.

The operation should be repeated until the adjustment is perfect.

The accuracy of the results obtained depends very largely upon the care with which the length of the base is determined.

It is claimed that with care results giving a p.e. of ^t 1 in 100 can be obtained.

The mekometer is the military range-finder adopted by the British Government. It consists of two instruments connected by a silk-covered hemp-base cord 25 (or 50) yds. in length.

The left-hand instrument has two fixed mirrors inclined at 45^ like those of an optical square, while the right-hand instrument has one mirror fixed and the other capable of rotation as in a box sextant.

The left-hand operator sights to the point A whose range is required and moves into such a position that the reflected image of the right-hand instrument coincides with the direct image of A, i.

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