## A Treatise on Military Surveying: Including Sketching in the Field, Plan-drawing, Levelling, Military Reconnoissance, Also a Particular Description of the Surveying Instruments Commonly Employed by Military Men, with Instructions for Using and Adjusting ThemW.H. Allen, 1847 - 344 pages |

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accuracy adjustment altitude artificial horizon ascertain barometer bearing bisect centre chain contour lines convenient correct cosine degrees depression direction distance divided divisions draw elevation equal error field-book fixed give given glass Greenwich ground half height hills Hindustani language horizontal circle inches instrument intersection Lachar latitude length limb longitude lunar distance Malaga mark means measured ment meridian meridian altitude method miles military sketching minutes moon mountain Nautical Almanac necessary needle object obtained off-sets operations paper parallax parallel parallel ruler perpendicular picket plane plate position protractor purpose reading reconnoissance refraction rhombus right angles rivers road Royal Engineers ruler scale screw sextant side sine slopes spirit-level square staff station sun's suppose surface survey surveyor taken tangent telescope theodolite tical tion triangle trigono trigonometrical Trigonometrical Survey true tube upper vane vernier yards zero

### Popular passages

Page 195 - ... but it may be made in a variety of ways, so as to revolve on any light portable stand. The tube, when required for use, is filled with water (coloured with lake or indigo), till it nearly reaches to the necks of the bottles, which are then corked for the convenience of carriage. On setting the stand tolerably level by the eye, these corks are both withdrawn, which must be done carefully and FRENCH REFLECTINQ-LEVEL.

Page 171 - THE first adjustment is that of the line of collimation; that is, to make the intersection of the cross wires coincide with the axis of the cylindrical rings on which the telescope turns : it is known to be correct, when...

Page 228 - SO'OO inches as the average height of the barometer at the level of the sea (which is however too much), the altitude of the upper station is at once obtained by inspection of Table I, correcting for temperature of the stratum of air traversed by table II.

Page 270 - ... 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. .

Page 173 - ... error must be corrected by turning the screw, B, and the other half by the two parallel plate-screws over which the telescope is placed. Next turn the telescope a quarter round, that it may lie over the other two screws, and make it level by moving them, and the adjustment will be complete. Before making observations with this instrument, the adjustments should be carefully examined and rectified, after which the screw B should never be touched ; the parallel plate-screws alone must be used for...

Page 145 - ... without any regard to thickness. This area, or the content of the plane figure, is estimated by the number of little squares that may be contained in it; the side of those little measuring squares being an inch, a foot, a yard, or any other fixed quantity.

Page 299 - What is the error of the best tables now in use ? hours, or one minute of space in two minutes of time. Therefore, if we make an error of one minute in observing the distance, we make an error of two minutes in time, or 30 miles of longitude at the equator. A single observation with the best...

Page 147 - ... in chains and decimals. Therefore, after the content is found, it will be in square links ; then cut off five of the figures on the right hand for decimals, and the rest will be acres. These decimals are then multiplied by 4 for roods, and the decimals of these again by 40 for perches.

Page 104 - ... the number of links to be deducted from each chain's length, in measuring up or down an inclined plane, to reduce it to the horizontal measure.