How beautiful beyond description must the heavens appear as viewed from the satellites of Jupiter! Viewed from the distance of Io, or Satellite I, the mighty planet Jupiter presents a spectacle such as the eye of man has never been privileged to behold. The huge flattened globe, ninety thousand miles in equatorial diameter, equal in mass to _three hundred planets such as our own_ and in volume to nearly _fourteen hundred_, fills a space in the heavens nearly twenty degrees in extent as viewed from this satellite. Fifteen hundred of our own full moons would hardly fill the same space. Whirling on its axis with frightful speed in a period of less than ten hours, the huge ball glides rapidly but majestically onward through the sky. A far distant sun shrunk to but one-fifth the diameter of the full moon throws light and shade across the rapidly changing surface of the planet, rich in the reds, browns and yellows and all the gorgeous shades and tints of its dense, seething, gaseous envelope. The phases of the moon on a greatly enlarged scale rapidly succeed each other on Jupiter as it is viewed from the satellite in all positions with reference to the sun. The cause of the belts of Jupiter, that lie parallel to the planet's equator and are constantly changing in number, width and shade, as well as the nature of all the peculiar splashes of color and intensely white flecks that come and go in the dense atmosphere of the planet would not be such a mystery to us were it possible to view the great planet from the distance of Satellite I, which is about as far from the surface of Jupiter as the moon is from the earth. It is uncertain whether the planet is entirely gaseous throughout or has a central core of solid or liquid matter. Its density is only one and one-quarter times that of water and slightly less than that of the sun, showing that it is composed largely, if not entirely, of matter in a gaseous state. Jupiter is a world as different from our own as it is possible to imagine. There is no visible surface crust and there are no permanent markings. Different spots on the planet's disk give different periods of rotation showing that it is atmospheric phenomena that we observe. All is constant flux and change on Jupiter. Dense vapors arise from a highly heated interior and spread out into belts parallel to the equator in the direction of the planet's rotation. From its nearest satellite all the interesting changes of color and form that constantly take place in the atmosphere of this great globe could be observed in great detail. The high percentage of light and heat that Jupiter reflects from the sun to its nearer satellites makes it a secondary sun to them of tremendous size though feeble strength.