Practical Geodesy ... |
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Practical Geodesy: Comprising Chain Surveying, and the Use of Surveying ... J. Butler Williams No preview available - 2018 |
Practical Geodesy: Comprising Chain Surveying, and the Use of Surveying ... J. Butler Williams No preview available - 2015 |
Common terms and phrases
accuracy adjustment adopted altitude angle of elevation angular distance appear artificial horizon ascer ascertained axis boundary Butser Hill calculation centre chain circle clamped column construction contained arc contour lines correction cross wires depression described determined difference direction drawn equal feet field field-book fixed fore sight given glass ground height hills horizontal angles horizontal lines inch inclosure index error instrument intersection Kit Hill latitude length limb line of collimation longitude marked means measured meridian method mile Nautical Almanac normal contours objects observed obtained offsets operations parallax parallel parish pickets placed plate plotting pole pole star position protractor purpose quantity reading reduction reference refraction rhombus right angles road rods scale screws sextant shade sides signals spirit-level staff star station line straight line surveyor taken telescope theodolite tion traced triangles Trigonometrical Survey vane vernier vertical arc zenith
Popular passages
Page 10 - Upon the same base, and on the same side of it, there cannot be two triangles that have their sides which are terminated in one extremity of the base equal to one another, and likewise those which are terminated in the other extremity.
Page 212 - ... fixing the index, and altering the position of the instrument to make the objects appear on the other wire ; if the contact still remains perfect, the axis of the telescope is in proper adjustment ; if not, it must be altered by moving the two screws which fasten, to the up-and-down piece, the collar into which the telescope screws. This adjustment is not very liable to be deranged.
Page 88 - ... the telescope brought down to the horizon ; a light, seen #' through a small aperture in a board, and held at some distance by an assistant, is then moved according to signals, until it is covered by the intersection of the spider's lines. A picket driven into the ground, under the light, serves to mark the meridian line for reference by day, when the angle formed by it and the magnetic meridian may be measured.
Page 210 - ... lower end of the frame of the glass. To examine the Parallelism of the Planes of the two Glasses, when the Index is set to Zero, This is easily ascertained ; for, after setting the zero on the index to zero on the limb, if you direct your view to some object, the sun for instance, you will see that the two images (one seen by direct vision through the unsilvered part of the horizon-glass, and the other reflected from the silvered part) coincide or appear as one, if the glasses are correctly parallel...
Page 211 - ... and call the minutes and seconds denoted by the vernier, the reading on the arc. Next place the index about the same quantity to the right of zero, or on the arc of excess, and make the contact of the two images perfect as before, and call the minutes and seconds on the arc of excess* the reading off the arc...
Page 97 - SDCBA, actually strikes on A. Now, it is a law of optics, that an object is seen in the direction which the visual ray has at the instant of arriving at the eye, without regard to what may have been otherwise its course between the object and the eye. Hence the star S will be seen, not in the direction AS, but in that of A s, a tangent to the curve SDCBA, at A. But because the curve described by the refracted ray is concave...
Page 211 - ... reading off the arc; and half the difference of these numbers is the index error; additive when the reading on the arc of excess is greater than that on the limb, and subtractive when the contrary is the case. EXAMPLE. Reading on the arc, . . 31
Page 210 - ... object passes exactly over or covers its image, as seen directly ; and any error is easily rectified by turning the small screw, i, at the lower end of the frame of the glass. To examine the Parallelism of the Planes of the two Glasses, when the Index is set to Zero. — This is easily ascertained ; for, after setting the zero on the index to zero on the limb, if you direct your view to some object, the sun for instance, you will see that the two images (one seen by direct vision through the...
Page 247 - AC and BD ; and in the triangle CAD, the sides AC, CD, with their contained angle ACD, being given, the base DA and the angle CDA are found by Case II. But the distances DA, DB being now given, with their contained angle ADB, the base AB is found by Prop. 20. PROP. XXV. PROB. The mutual distances of three remote objects being given, with the angles which they subtend at a station in the same plane, to find the relative place of that station.
Page 53 - ... of those metals which alone are applicable to such uses; and their own weight, however symmetrically formed, must always be unequally sustained, since it is impossible to apply the sustaining power to every part separately : even could this be done, at all events force must be used to move and to fix them; which can never be done without producing temporary and risking permanent change of form.