National Geographic : 1899 Aug
MAGNETIC WORK OF COAST AND GEODETIC SURVEY 289 corrections for secular variation will be made with the aid of observations repeated at certain intervals at so-called " repeat" or " secular variation " stations. The Survey likewise is cooper ating with the various state geologists in the carrying out of detailed state magnetic surveys. This work consists in the estab lishment, at the county-seats, of true meridian lines for the use of the surveyor and in the detection and mapping out of regional magnetic disturbances and the correlation of the latter with geologic formations. 2. Magnetic Survey of Ocean Areas. When the great rble which the compass plays in the art of navigation is recalled, it seems remarkable that our country has done so little systematic work in the determination of magnetic elements at sea. In supplying compass directions on its charts the Survey is feeling keenly the need of more accurate data. It is a well-known fact that at the very places-near coast lines and over submerged land areas where danger from shipwrecks is greatest the compass directions, taken from present charts of the lines of " equal magnetic varia tion," are weakest. At these places these lines will present the same peculiar curvatures and interlacings that we find over the land areas. The Survey therefore proposes to contribute its ade quate share toward remedying these defects and is making ample provision for carrying on such work systematically in the future. This work will be of a twofold character: a. Determination of magnetic elements at shore stations. h. Determination of magnetic elements at sea, the. dip and relative intensity being obtained with the Fox dip circles. 3. Continuous Observations at Magnetic Observatories. To make possible the rapid and economical execution of the plans just set forth, three well-equipped magnetic observatories will be established, viz., one near Washington city (this to be the cen tral or standard observatory, at which the constants of all mag netic instruments will be determined), one on the Pacific coast, and another on the Hawaiian islands. These observatories, with the cooperation of those at Toronto, Habana, Mexico, and Manila, and some temporarily established observatories for re cording the variations of the declination, will suffice for the practical needs of the magnetic survey work. Their function will be to record and to fix the countless variations and fluctua tions of the earth's magnetism and thus make possible the re duction of all magnetic observations to a common epoch.