These Galilean Satellites have proved of great value in two respects : ( 1) the observed variations in the times of the eclipses of i. with the varying distance of the earth from Jupiter led Romer in 1675 to the discovery of the motion of light and the first determination of its velocity; (2) observations of the phenomena of the satellites were formerly much used for the determination of longitudes by comparing the calculated times of their occurrence, at Greenwich, for instance, with the local times of the place at which they were observed. Of the remaining satellites, v., which is the nearest of all to Jupiter, is in conse quence of its smallness and its proximity to the planet visible only in the large instruments. About the same mean distance from the planet, viz., rather over 7,000,000 miles, are vi. and vii., which are also very small. Their two orbits interlock like two links in a chain, but their planes are inclined to one another at an angle of about 28°. Somewhat similar conditions hold for the orbits of vim and ix., of which the mean distances are of the order of 15,000,000 miles, and the periods of revolution slightly more than two years. Owing to their great remoteness from Jupiter they I are subject to enormous perturbations by the sun. The motion
of both these satellites, like that of Phoebe, the outermost satel lite of Saturn, is retrograde. (T. E. R. P.) JUR (DiuR), the Dinka name for a tribe of negroes of the upper Nile valley, whose real name is Luoh, or Lwo. They appear to be immigrants from the south ; they now occupy a district of the Bahr-el-Ghazal between the Bongo and Dinka tribes. Of a reddish black colour, fairer than the Dinka, they are well pro portioned, with the hair short. Tattooing is not common, but when found is similar to that of the Dinka; they pierce the ears and nose, and in addition to the ornaments found among the Dinka wear a series of iron rings on the forearm covering it from wrist to elbow. They are mainly agricultural, but hunt and fish to a considerable extent ; they are also skilful smiths, smelting their own iron, of which they supply quantities to the Dinka. Their chief currency is spears and hoe-blades, and cowrie shells are used in the purchase of wives. Their chief weapons are spears and bows.
See G. Schweinfurth, The Heart of Africa: Travels 1868-1871, trans. G. E. E. Frewer (2nd ed., 1874) W. Junker, Travels in Africa (Eng. ed., 189o-92).