A TREATISE ON THE PRINCIPLES AND PRACTICE OF LEVELLING |
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Page 18
... cross level , placed at 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 ...
... cross level , placed at 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 ...
Page 20
... cross the wires obliquely , and any want of verticality in the staff will be immediately detected , and the ob- server must signal to the staff - man accordingly . The advantages from the use of the modern staves , over those of the old ...
... cross the wires obliquely , and any want of verticality in the staff will be immediately detected , and the ob- server must signal to the staff - man accordingly . The advantages from the use of the modern staves , over those of the old ...
Page 26
... cross it precisely at W , the common focus of the two glasses , where the image of the staff ( or distant object ) is formed , and there- fore the wires and the staff will appear to an observer as one object , or , at least , equally ...
... cross it precisely at W , the common focus of the two glasses , where the image of the staff ( or distant object ) is formed , and there- fore the wires and the staff will appear to an observer as one object , or , at least , equally ...
Page 27
... cross wires are fixed to a plate , called a dia- phragm , attachedby screws to the slide G H , which also carries the slide D F of the eye - piece . The point W , or focus of the object glass , does not remain constant for terrestrial ...
... cross wires are fixed to a plate , called a dia- phragm , attachedby screws to the slide G H , which also carries the slide D F of the eye - piece . The point W , or focus of the object glass , does not remain constant for terrestrial ...
Page 28
... cross wires , which will be the case if they seem to be attached to each other , or , in other words , appear equally distant from him ; and the moving about of the observer's eye does not detect any apparent dis- placement of the staff ...
... cross wires , which will be the case if they seem to be attached to each other , or , in other words , appear equally distant from him ; and the moving about of the observer's eye does not detect any apparent dis- placement of the staff ...
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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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