Precise Leveling in the United States 1903-1907

Hayford, John Fillmore; Pike, L.

Bibliographic data

Monograph

Persistent identifier:: 883838079

Author:: Hayford, John Fillmore; Pike, L.

Title:: Precise Leveling in the United States 1903-1907

Sub title:: with a readjustment of the level net and resulting elevations

Scope:: 280 Seiten, 1 Karte

DOI:: 10.14463/GBV:883838079

Year of publication:: 1909

Place of publication:: Washington

Publisher of the original:: Government Printing Office

Identifier (digital):: 883838079

Illustration:: 1 Karte

Language:: English

Usage licence:: Public Domain Mark 1.0

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2017

Document type:: Monograph

Collection:: Earth sciences

Chapter

Title:: INSTRUCTIONS FOR PRECISE LEVELING.

Document type:: Monograph

Structure type:: Chapter

10 PRECISE LEVELING IN THE UNITED STATES, 1903-1907. on which readings are made to millimeters by estimation. This type is described in Appendix 8, Report for 1899, pages 418-419. In August, 1903, the experiment was made of using a point marked on the top of the rail of the railroad track as the rod support.* A full account of this experiment with the results is given on pages 416-418 of Appendix 6, Report for 1904; entitled “Precise Leveling from Red Desert, Wyo., to Owyhee, Idaho, 1903.” The most prominent effect was to change the rate of accumulation of discrep ancy between the forward and backward lines. This is a clear confirmation of the theory that the accumulated discrepancy is due mainly to systematic rising or set tling of rod supports. This theory is based upon the frequently observed fact that when a change is made in the method of rod support or in the habits of the rodman, a change is liable to take place in the rate of accumulation of discrepancy between the forward and backward lines. The evidence showed clearly that the use of the rail for the rod support increased both the speed and accuracy of the leveling, and the practice has been adopted in all Coast and Geodetic Survey leveling since that time. Two uncertainties in connection with this method of rod support will occur to anyone who considers it carefully, namely, the uncertainty as to whether the rodman holds the foot of the rod for both foresight and backsight on precisely the same point on the slightly rounding and sometimes inclined surface of the top of the rail, and the uncertainty as to the recovery by the rail of its former elevation after a train has passed over it. The first of these uncertainties is very small, provided the rodman is careful. No difficulty was found in marking the exact spot on the rail which was used in such a way, with chalk or keel, that the mark was recoverable, even after a train had passed over it. Direct observations have indicated that, as a rule, the rail rises to sensibly its former elevation quickly after a train passes. Doubtless there are exceptional cases. The best proof available that such cases are comparatively rare for the conditions under which the rail was used as a rod support, and that the systematic permanent settling of the rail caused by the passage of the train is exceedingly small, is furnished by the comparison given in Appendix 6, Report for 1904, of the accuracy of the leveling by each party before and after beginning the use of the rail as a rod support, and this has been confirmed by the good results obtained on later lines. The footpins were carried along with each party during the progress of the leveling and were used whenever a train was known to be approaching, or when there were special reasons for supposing that the track was not in as stable a con dition as usual. The results are not subject, therefore, to the possible uncertainty arising from the action of every train. INSTRUCTIONS FOR PRECISE LEVELING. The general instructions issued to the leveling parties in 1908 are given below. Those issued in 1903-1907 differ from these only in minor matters and in not being so complete. * Mr. F. W. Perkins, Assistant Superintendent, who was the observer on the line from Washington to Annapolis, 1875, states that the rods were supported upon the railroad rails, although that fact was not especially noted in the record, as this was the ordinary practice at that time.

Access restriction

Copyright

fullscreen: Precise Leveling in the United States 1903-1907

Monograph

Chapter

Table of contents

Cite and reuse

Monograph

Chapter

Image

Image fragment

Citation links

Citation recommendation