Principal Facts of the Earth's Magnetism and Methods of Determining the True Meridian and the Magnetic Declination, Volume 4

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U.S. Government Printing Office, 1909 - Geomagnetism - 99 pages
 

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Page 15 - the sailors, moreover, as they sail over the sea, when in cloudy weather they can no longer profit by the light of the Sun, or when the world is wrapped up in the darkness of the shades of night, and they are ignorant to what point of the...
Page 34 - Let whosoever would make the same experiments, handle the bodies carefully, skilfully and deftly, not heedlessly and bunglingly ; when an experiment fails, let him not in his ignorance condemn our discoveries, for there is naught in these Books that has not been investigated and again and again done and repeated under our eyes.
Page 84 - XVI the azimuth of Polaris corresponding to the latitude of the station and year of observation; find the natural tangent of said azimuth and multiply it by the distance from the peep sight to the rod; the product will express the distance to be laid off from the rod exactly at right angles to the direction already determined (to the west for eastern elongation or to the east for western elongation) to a point which with the peep sight will define the direction of the true meridian with a fair degree...
Page 84 - ... and Polaris. To reach elongation, the star will move off the plumb line to the east for eastern elongation, or to the west for western elongation, therefore by moving the peep sight in the proper direction, east or west, as the case may be, keep the star on the plumb line until it appears to remain stationary, thus indicating that it has reached its point of elongation. The peep sight will now be secured in place by a clamp or weight, with its exact position marked on the rest, and all further...
Page 81 - ... for every degree north of 40. Reverse these operations for correcting times of east elongation. e. To Refer to Any Other than the Tabular Longitude. — Add...
Page 83 - Attach the plumb-line to a support situated as far above the ground as practicable, such as the limb of a tree, a piece of board nailed or otherwise fastened to a telegraph pole, a house, barn, or other building affording a clear view in a north and south direction. The...
Page 86 - ... surveyor and give results with all desirable precision. They do not require an accurate knowledge of the time, which is their principal advantage. The relative motion of the stars employed. when near the meridian and the unchangeable azimuth of Polaris at elongation (so far as the 'surveyor is concerned), indicate with sufficient exactness the moment when the observation should be made. Stormy weather, a hazy atmosphere, or the presence of clouds, may interfere or entirely prevent observation...
Page 28 - by the Isle of Saint Michaell in the Acorres," he found "that the North poynt of the common compass, showeth the Pole very neere in that Meridian, but the bare Needle sheweth about 4 Degrees 50 Minutes to the Eastwards of the Pole." It was not until the close of the sixteenth century that the "variation from the true north" came to be generally accepted as an actual fact of nature and not one to be accredited to the imperfection of the construction of the compass. By referring again to Figure 8 it...
Page 24 - Azores ; for in sailing thence westward the ships went on rising smoothly towards the sky, and then the weather was felt to be milder, on account of which mildness the needle shifted one point of the compass ; the further we went the more the needle moved to the northwest, this elevation producing the variation of the circle which the North star describes with its satellites...
Page 14 - ... mustard seed. Hang it up in a place where there is no wind. Then the needle constantly shows the south; but among such needles there are some which, being rubbed, indicate the north. Our soothsayers have some which show south and some which show north. Of this 14 MAGNETIC DECLINATION TABLES FOR 1902. property of the magnet to indicate the south, like that of the cypress to show the west, no one can tell the origin.

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