Hydrographical Surveying: A Description of the Means and Methods Employed in Constructing Marine ChartsMurray, 1898 - 388 páginas |
Otras ediciones - Ver todas
Hydrographical Surveying: A Description of Means and Methods Employed in ... William James Lloyd Wharton Sin vista previa disponible - 2016 |
Términos y frases comunes
accuracy artificial horizon ascertain azimuth base beacon beam compass boat Breastmark calculated centre chart chord chronometers coast coast-line commencement compass convenient convergency correct difference of longitude direction dist elevation equal altitudes equation of equal error fathoms fixed give Gnomonic Projection height heliostat hour angle HYDROGRAPHICAL SURVEYING inches instrument intersection interval knots latitude Length in Feet limb low water lunitidal interval main stations mark Markab mean measured meridian altitude meridian distance method miles minutes nautical necessary noon object observations obtained ordinary paper plotted points pole position prick protractor result right angles right ascension round running survey scale sea rate sextant sheet ship shore side sidereal sketch sounding spot stars station pointer surveyor taken telescope temperature theodolite tide tion transit triangulation true bearing vernier Vers versine vertical watch wire zero ΙΟ
Pasajes populares
Página 169 - ... should be established, recording the date and height above such mean level. Even recording the height to which the tide rose on a certain day and time would render a comparison possible in future years. A good determination of the mean sea-level by the simple operation of taking means may be made, in less than two days, with even a moderate number of observations properly distributed so as to subdivide both solar and lunar days into not less than three equal parts. Suppose, for example, we choose...
Página 37 - Across it are nailed crossed strips of copper with a white cardboard disc, about an inch in diameter, fastened to their centre. ' The rod that carries this ring slips up and down in a hole at the end of the arm, and is clamped by a retaining screw. ' In the centre of the back of the mirror a hole of about \ inch diameter is scraped in the tinfoil, being careful to leave a sharp edge.
Página 170 - ... observations in the series ; and if either m or n be a multiple of 3, or of a larger number, the whole series may be divided into two or more series having no observation in common, and each complete in itself. The accuracy of the method can thus be tested, by comparing the means obtained from the separate sub-series of which the whole is made up. Should the ship's stay not permit of the employment of the above method a very fair determination may be made in less than a day, by taking the mean...
Página 170 - The theoretical error of this method is very small, and the result thus obtained is decidedly to be preferred to the mere mean of the heights at high and low water. " The mean level thus determined is subject to meteorological influences, and it would be desirable, should there be an opportunity, to redetermine it at the same place at a different time of year. Should a regular series of observations for a fortnight be instituted, it would be superfluous to make an independent determination of the...
Página 16 - ... the telescope, maintains its position during a complete revolution, the external azimuthal axis is truly parallel with the internal, and both are vertical at the same time ; but, if the bubble does not maintain its position...
Página 169 - ... 00 80 16 0 8 16 16 16 24 16 16 32 24 32 32 32 The observations may be regarded as forming three groups of three each, the members of each group being separated by 8 hours solar or lunar, while one group is separated from the next by 8 hours lunar or solar. In the mean of the...
Página 16 - ... of its run by turning these screws. The bubble will now retain its position while the vernier plate is turned completely round, showing that the internal azimuthal axis about which it turns is truly vertical. The bubbles of the levels on the vernier plate, being now, therefore, brought to the...
Página 15 - Bring the bubble, b, of the level, ss, beneath the telescope to the center of its run by turning the tangent screw, i. Turn the vernier plate half round, bringing the telescope again over the same pair of the parallel plate screws ; and, if the bubble of the level be not still in the center of its run, bring it back to the...
Página 56 - On low coasts and islets flag staffs upwards of loo ft. high made of several spars lashed together must sometimes be erected in order to get the necessary range of vision. A fixed beacon can be erected in shallow water by constructing a tripod of spars about 45 ft. long. The heads of two of them are lashed together and the heels kept open at a fixed distance by a plank nailed at about 5 ft. above the heels of the spars. These are taken out by three boats and the third tripod leg lashed in position...
Página 38 - ... when the mirror is at a large angle, and also the beam of light will be dispersed before it has traversed many miles. It is well to have the mirror a fair size, say 6 in. square, as in practice it will be found generally necessary, in order to save time, after once adjusting the flash, to leave a man to keep it on while the surveyor is taking his angles ; and although a man will soon pick up the knack, a larger mirror will allow for eccentricities on his part, and also, on a dull day, a faint...