## A TREATISE ON THE PRINCIPLES AND PRACTICE OF LEVELLING |

### From inside the book

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**right angles**. If the earth were an ex- tended plane , all lines representing the direction of gravity at every point on its surface would be parallel to each other ; but , in consequence of its figure being that of a sphere or globe ... Page 6

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**right angles**to the horizontal line A B. Now if the surface was undulatory , as shown by the curved line A B , and it was required to make a section represent- ing it , an instrument capable of tracing out a line parallel to the ... Page 7

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**right angles**to the radius of the circle ( or semi- diameter of the earth ) , I C. A line which is parallel to the sensible horizon of the observer , is the line traced out by our spirit - levels ; it is parallel to a tan- gent to the ... Page 18

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**right angles**to the principal level , which affords very great facility in setting up the instrument , and adjust- ing for observation , as will be hereafter described ; it likewise has a reflecting mirror , mounted with a hinge joint ... Page 26

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**right angles**to it , and separated so as to admit , at usual distances , the staff e to appear between them , by which the observer can always tell if the staff - man holds it erect in a lateral direction , as before explained . The ...### Other editions - View all

### Common terms and phrases

50 base adjustment approximate point b₁ b₂ back sight back staff bench mark calculations centre line centre stake chain clinometer Cloth computed half width construction correct cross wires curvature curve cuttings and embankments datum line depth of cutting determined diagram difference of level direction distance Dover Castle Dumpy Level earth edition engraving equal example field-book Folkstone Foot of bank Fore Sight forward reading forward station give gradient ground Gunter's chain horizontal line hypothenuse Hypsometry Illustrated inches inclined plane instrument J. P. WHITNEY length line A B lines of railway mean height measured Merrimack River method middle area mile object glass observer obtain outer rail parallax perpendicular placed plates point a₁ point H practice radius ratio Reduced Levels refraction represent right angles slope spirit-level stones subtracted superelevation surveyor Tables tangent telescope theodolite tion Top of bank Treatise turnpike road yards

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