The third moon, Europa, is rather smaller, takes over three days to its journey, and suffers eclipse once in every eighty-five hours. The fourth moon, Ganymede, is believed to be considerably larger than Mercury, journeys round Jupiter once a week, and is eclipsed once every hundred and seventy-one hours. The fifth moon, Callisto, is also said to be slightly larger than Mercury, performs its journey in something more than sixteen days, and from its greater distance suffers eclipse less often than the other four. The distance of the nearest is more than one hundred thousand miles from Jupiter; that of the farthest, more than one million miles. The following table presents more minutely the results of the latest discoveries concerning these satellites: +-----------------------+----------------+------------+-----------+ | | DISTANCE FROM | | PERIOD OF | | SATELLITES. | CENTER OF | DIAMETER. |REVOLUTION.| | | JUPITER. | | | +-----------------------+----------------+------------+-----------+ | | | |D. H. M. S.| |1. Barnard’s Satellite,| 112,500 miles.| 100 miles.| 11 57 23| |2. Io, | 266,000 ” |2,356 ” | 1 18 27 33| |3. Europa, | 424,000 ” |2,046 ” | 3 13 13 42| |4. Ganymede, | 676,000 ” |3,596 ” | 7 3 42 33| |5. Callisto, |1,189,000 ” |2,728 ” |16 15 32 11| +-----------------------+----------------+------------+-----------+ The fact of these eclipses, and of the shadow thrown by Jupiter’s body, shows plainly that though he may give out some measure of light, as has been suggested, yet that light can not be strong, or it would prevent any shadow from being thrown by the sunlight. Also, the dense masses of cloud around him, though reflecting sunlight brightly, would shut in much of his own light. Possibly it is chiefly as heat-giver and as sunlight-reflector that Jupiter serves his five satellites. As with our own moon, so with Jupiter’s moons, the real center of their orbit is the sun, and not Jupiter. They accompany Jupiter in his journey, controlled by the sun, and immensely influenced by Jupiter.