The transits of the satellites across the Jovian disk present many curious appearances, due to complicated and changeable effects of light and shade both upon the planetary background and upon the little circular objects self-compared with it. These, in the ordinary course, show bright while near the dusky limb, then vanish during the central passage, and re-emerge again bright at the opposite side. But instead of duly vanishing, they now and then darken even to the point of becoming indistinguishable from their own shadows, by which they are preceded or followed. This difference of behavior can not be attributed wholly to varieties of lustre in the sections of the disk transited; otherwise it could be predicted. But this has never been attempted; “black transits” come when least expected. The third and fourth satellites are those chiefly subject to these phases; the second has never been known to exhibit them; and they but slightly affect the first. Indeed, all the satellites, except, perhaps, No. II, are striped or spotted; and this leads to seeming deformations in their shape, as well as fluctuations in their brightness, the markings being evidently of atmospheric origin, and hence changeable. Their distinct and accurate perception has been made possible by the excellence of the Lick 36-inch refractor. Jupiter’s moons seem to resemble him in constitution. The first three possess the same high reflective power. No. II is as bright as the planet’s brightest parts, so that its albedo can not fall short of 0.70. And even No. IV (formerly designated “Calypso” in reference to its frequent obscurations) exactly matches, during its darkest phases, the blue-gray polar hoods of its primary. On an average, too, the satellites seem to be of about the same mean density as Jupiter, No. I being considerably the lightest for its bulk; and their spectra, according to Vogel’s observations in 1873, are composed of solar rays modified in precisely the same way as those reflected by the planet. The discovery, September 9, 1892, of Jupiter’s “fifth satellite” was one of the keenest astronomical surprises on record. Professor Barnard seized the opportunity, lent by the specially favorable opposition of 1892, to rummage the system for novelties. Keeping the telescopic field dark by means of a metallic bar placed so as to occult the gorgeous planetary round, he sought, night after night, for what might appear. At length, on September 9, he caught the glimmer he wanted, and made sure, September 10, that it truly intimated the presence of a new satellite.