## Outline of the Method of Conducting a Trigonometrical Survey, for the Formation of Topographical Plans: And Instructions for Filling-in the Interior Detail, Both by Measurement and Sketching : Military Reconnaissance, Leveling, &c., &c., with the Explanation and Solution of Some of the Most Useful Problems in Geodesy and Practical Astronomy, to which are Added a Few Formulę and Tables of General Utility for Facilitating Their CalculationJohn Weale Architectural Library, 1840 - 200 pages |

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accuracy adjusted altitude angle of depression angles of elevation apparent ascertained Astronomy axis azimuth base calculated centre chain chronometer circle column contour contour lines correction curvature degree determined diameter difference of latitude difference of longitude direction earth equal feet field-book figure fixed Geodesie Greenwich Greenwich mean ground height horizontal line inches index error instrument intersection interval laid latitude length longitude marked mean measured meridian method miles mountain barometer Nautical Almanac necessary object observed angles obtained Ordnance Survey parallax parallel perpendicular pickets plane plotting pole protractor purpose radius reciprocal angles refraction right angles right ascension rods scale screw semidiameter sextant sidereal sides sketch slopes spherical excess spirit-level staff star stations subtracted surface Survey of Ireland taken tangent telescope temperature theodolite thermometer tion topographical Townlands triangles trigonometrical points Trigonometrical Survey tube vane vernier vertical arc vertical distances zenith distance zero

### Popular passages

Page 134 - Day is the interval of time between two successive transits of the sun over the same meridian; and the hour-angle of the sun is called Solar Time.

Page 134 - PZ, it follows that the altitude of the elevated pole is equal to the latitude of the place of observation. The triangle ZPM then (however much it may vary in shape for different positions of the star...

Page 111 - Wales," will be found all the details connected with the measurement of an arc of the meridian, extending from Dunnose in the Isle of Wight, to Clifton in Yorkshire. The calculations are resumed at page 354« of the third volume ; the length of one degree of the arc resulting from which, in latitude 52° 30...

Page 145 - Z S") when to the north below the pole. Perhaps the rule given by Professor Young for the two first cases is more simply expressed thus : — Call the zenith distance north or south, according as the zenith is north or south of the object. If it is of the same name with the declination, their sum will be the latitude ; if of different names, their difference ; the latitude being of the same name as the greater. EXAMPLE I. On April 25, 1838, longitude 201 30s east, the meridional double altitude of...

Page 46 - ... till it is passed, and then returning in the same manner to the original line. But perhaps a more convenient method is to measure on a line making an angle of 60° with the original direction a distance sufficient to clear the obstacle, and to return to the line at the same angle, making CD = BC'; the distance BD is then equal to either of these measured lines. The distance from B on the line...

Page 83 - ... 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.

Page 6 - ... the expansion of which is five, the two being riveted together at the centre C ; DE and de are the iron tongues pinned on to the bars, so as to admit of their expansion, with the platina dots at D and d. The tongues are by construction made perpendicular to the rods at a mean temperature of 60° Fahrenheit, and the expansion taking place from their common centre, when A expands any quantity which may be expressed by three, B expands at the same time a quantity equal to...

Page 83 - AB is a hollow tube of brass, about half an inch in diameter, and about 3 feet long ; c and d are short pieces of brass tube of larger diameter, into which the long tube is soldered, and are for the purpose of receiving the two small bottles, e and/, the ends of which, after the bottoms have been cut off, by tying a piece of string round them when heated, are fixed in their positions by putty or white lead ; the projecting short axis, g, works (in...

Page 83 - ... 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 when the tube is nearly level, or the water will be ejected with violence; and the surface of the water in the bottles, being necessarily on the same level, gives a horizontal line in whatever direction the tube is turned, by which the vane of a levelling staff is adjusted.

Page 13 - Fresnel & Arago, and used by them in co-operation with Colonel Colby and Captain Kater. By means of this a station 48 miles distant was observed. The most powerful night signal is, however, Drummond's light. This was invented by Lieutenant Drummond, and consists of a ball of lime about \ in. diameter placed in the focus of a parabolic reflector and raised to an intense heat by a stream of oxygen gas directed through a flame of alcohol. This produces a light eighty times the intensity of an Argand...