Longitude

(lon'je-tūd.) [From L. long it udo, length. (Geog.) The angle between two meridional planes, one pa ing through a particular station, the other a fixed plane of reference. L. is commonly measured E. and W. of the fixed meridian through 180°. In America the meridian of Washington is adopted as the origin whence longitudes are measured. In this work, however, longitudes are calculated from the English meridian of Green wich, which is still of more common use. The determination of the L. of any station on the earth, whether on land or on the ocean, is of the utmost importance to the astronomical observer, the traveller, and the seaman. The problem is not an easy one. It is not difficult to determine the latitude of any station since there is an actual change in the aspect of the heavens (for every hour) with any change of latitude. But in travelling from E. to W., or from W. to E., there is no change in the aspect of the heavens; the stars seen at any moment in one L. being situated precisely as they would be seen, though not at the same moment, from any other station in the same latitude. All methods of determining the L. are based on the fact that the apparent time is different for two places separated by any distance in L. The sun or any given star will cro the celestial meridians of the two places at different hours, and so also any celestial phenomena will occur at different hours of apparent time. On the other hand, the occurrence of any phenomenon indicative of apparent time, as the sou thing of the sun or a star, will take place at different hours of absolute time. For places on land any method by which the difference of time at two stations can be determined will serve to determine their difference of L.; but for observations to be made at sea other methods must be adopted. One method is to observe the altitude of the sun at about that part of the day when his altitude is changing most rapidly. This altitude being determined, and the latitude and time of observation known (the latter from the chronometer), the L. can be calculated. Long-legs, (-legz.) (Zool.) See PHALANGITA. [s. 554]