Page:Popular Science Monthly Volume 16.djvu/778

744. Some Merz telescopes add, from their defects, a purple tint; and an instrument of another maker gives the spot the color known as Venetian red. Dr. Pigott, who has a With-Browning silvered mirror instrument, and a fine refractor by Wray, finds the latter so unusually well corrected that its performance coincides closely with that of the former. Color-changes, both as regards time and intensity, may be caused by the greater or less translucency and refracting powers of the atmosphere through which any object is seen; but they may also very frequently arise from the greater or less heat and luminosity of solid or viscid matter below the cloudy strata, and from important modifications of chemical action. Between September 3d, at from 10.45 to 10.55, and October 4th, 10.40 , Captain Noble's drawings, made at Maresfield, show a great change in the aspect of the planet, affecting the brightness and the tint of enormous spaces. Parts above the great spot which were brilliant on the former occasion had become cloudy, and, southeast of the spot, there came a round white spot, with very dark surroundings. These changes must have affected many millions of square miles.

On October 16th, at 10.5, he noticed the color of the red spot "more marked than ever." There were also extensive changes in the belts, and the polar regions were more cloudy. He made the following entry in his note-book: "It is a most noticeable feature; the red spot reposes like an island in the middle of a light space on the planet's disk, and the belts, north and south of it, seem in a great measure to conform to its curved outline. This would indicate a disturbance of a stupendous character, from the amount of the area involved."

On the whole, during the season for observation of 1879-'80 Jupiter has been more than usually interesting. From pole to pole changes of great magnitude have been produced with prodigality of violence rather than with economy of time. Perhaps the mighty planet is still in the stage of youth, with blazing and explosive energies that a few hundred thousands of years may be required to tame down to the soberness of our comparatively quiescent earth.—Belgravia.

—The red spot spoken of above was watched by an astronomer in this country, Mr. E. Leopold Trouvelot, of the observatory at Cambridge, during a part of 1878. He has published an account of his observations in "The Observatory," and has furnished to "La Nature" two views of the spot as seen at times three months apart, which we reproduce. In his published description, Mr. Trouvelot says that in looking at Jupiter on September 25, 1878, at six hours and fifty minutes, he noticed a remarkable red spot a little above the southern border of the equatorial belt, with its center situated a little to the east of the central meridian. It occupied apparently about one fifth of the diameter of the planet, and was quite distinct, its intense rose-color forming a striking contrast with the luminous white ground on which