_Occultations of Jupiter by the Moon._—Phenomena of this kind are always awaited with keen interest by the possessors of telescopes; but it is rarely that all the circumstances are favourable. The first recorded instance appears to have been in A.D. 847. In 1792, on April 7, Schröter observed an occultation of this planet, with a desire to verify his suspicion of a lunar atmosphere. He saw that “some of the satellites became indistinct at the limb of the Moon, while others did not suffer any change of colour. The belts and spots of Jupiter appeared perfectly distinct when close to the limb of the Moon.” On Jan. 2, 1857, an occultation took place under conditions which rendered it visible to many observers in this country, and the most interesting fact elicited was that at emersion a dark border was seen attached to the arc of the Moon projected on the planet. Mr. Lassell described this dark border as “a shadowy line, in character, magnitude, and intensity extremely like Saturn’s obscure ring projected on the ball.” During the thirty years following 1859 only two occultations visible in England occurred, and the last of these, on August 7, 1889, was widely observed. On this occasion Capt. Noble and others redetected the shadowed edge of the Moon seen by Lassell in 1857. “It was a strongly marked shading, following the outline of the Moon’s limb.” At Bristol I recorded that, at the disappearance, the outer margin of our satellite was fringed with light where it crossed the planet; but at the reappearance this effect had vanished, and the appearance was perfectly normal. The disk of Jupiter, where it met the edge of the lunar disk, looked dusky by the effects of contrast; but I saw no marked shading with a sharply terminating boundary, such as appears to have been remarked elsewhere. As the planet emerged definition was superb, the belts were lividly distinct, and the spectacle was one of the prettiest that could be imagined. The red spot was going off the W. limb, and the disk was covered with belts; many of them near the poles were extremely narrow, like fine lines drawn with a sharp lead pencil. I used a 4-inch refractor, powers 65 and 145, with this instrument the foregoing sketch was made. The exceptional distinctness of the Jovian markings on this occasion shows that the proximity of the Moon has certainly no tendency to efface planetary details, but rather to intensify them[34]. On Sept. 3, 1889, an occultation of Jupiter was visible in America, and observed by Mr. Brooks at Geneva, N.Y., with a 10-1/8-inch equatoreal. His drawing, made from a photograph and eye-observations, shows nothing of a dark fringe bordering the Moon’s limb. [Illustration: Fig. 36. Jupiter and satellites seen in a small glass.] _The four Satellites._—When Galilei directed his telescope to Jupiter on the evening of Jan. 7, 1610, he saw three small star-like points near the planet; so:— [Illustration] On Jan. 13 he discovered a fourth; thus:— [Illustration]