## A treatise on surveying, Volume 2 |

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accuracy accurate adjustment altitude astronomical axis azimuth base calculated celestial celestial pole centre chain chord chronometer circle computed Corr correction curve declination determined dial difference direction earth equal equator error feet fixed stars formula given graduated Greenwich Greenwich mean height high water horizontal hour angle hypsometer inches instant instrument intersection intervals latitude length longitude low water lunar mark measured meridian method micrometer miles minutes moon Nautical necessary notch observations obtained parallel perpendicular plane plane-table plotted plumb-bob point of Aries polar pole position prime vertical projection radius refraction right angles right ascension scale screw sextant side sidereal solar sphere spherical trigonometry staff station straight stream subtended sun's surface survey surveyor tacheometer taken tangent line tangential angle telescope temperature theodolite tidal tide transit trigonometry upper velocity vernier vide fig wire zenith distance zero

### Popular passages

Page 89 - The longitude of a place is the arc of the equator intercepted between the meridian of that place and some assumed meridian to which all others are referred.

Page 147 - Ocean, the first thing which strikes us is, that, the north-east and south-east monsoons, which are found the one on the north and the other on...

Page 79 - Having given two sides and the included angle, or two angles and the included side.

Page 69 - ... often takes many hours) before it can be considered fit for use ; and, if this precaution be not attended to, the whole E of the work, after having set very hard on the surface, cracks and becomes a friable mass, from the slaking of the refractory particles after the body of the concrete has set. The reader is referred, for further information on this subject, to the volume of this series on " Foundations and Concrete Works.

Page 16 - ... by moving the telescope vertically, and read the two ends. Read the height of the crosswires on the rod. Bring the bubble near the other end of tube and read both the bubble and rod. Repeat many times. Reduce the work by taking the half-difference of the two end readings in each case, thus giving the distance of the centre of the bubble from the centre of tube for each position. Take the mean of these results for each set of end readings separately. If these mean results were for opposite ends...

Page 44 - The greatest care was taken during each of the measurements to secure correct alignment, to adjust differences of level, to estimate variations due to temperature, and to allow for all other possible sources of error. Where each day's work left off, a fine plumb-line was suspended to mark it off, the plummet vibrating in a brass cup, sunk in the ground and filled with water.

Page 78 - That is, the sines of the sides of a spherical triangle are proportional to the sines of the opposite angles.

Page 9 - ... the plane of the sextant. The simplest test of its perpendicularity is the following. Set the index near the middle of the arc; then, placing the eye very nearly in the plane of the sextant, and near the index glass, observe whether the arc seen directly and its reflected image in the glass appear to form one continuous arc, which will be the case only when the glass is perpendicular.

Page 10 - ... which are placed two wires parallel to each other, and equidistant from the centre, to which are generally added two others at right angles to these, and parallel to each other. By means of these wires the adjustment may be made thus : screw on the telescope, and turn the tube containing the eyeglass till two of the wires are parallel to the plane of the instrument ; then take two objects, as the sun and moon, or the moon and a star, or two stars, whose angular distance must not be less than...

Page 83 - A, 4 cos 6 = cos c cos a + sin c sin a cos B, > (1) . , "cos c = cos a cos b + sin a sin b cos C. J Whence . cos a — cos b...