At some remote period, when only part of the now solid earth had been condensed from gaseous and vapory matter, our planet might have had a mean density like that of Jupiter, as its rocky materials contain between forty and fifty per cent, of oxygen; and while condensations and chemical combinations were going on rapidly our globe must have been the scene of
"Thunders, lightnings, and prodigious storms."
And it is probable that certain stars which have suddenly blazed forth with passing splendor have exhibited to us the spectacle of conflagrations extending over millions and billions of square miles. Color changes in Jupiter—such as those noticed by Mr. Browning and the writer in 1869-'70—may have been caused by soda-flames, though not fierce enough or extensive enough to add materially to his ordinary luminosity, which is estimated as always exceeding, though not in a very high degree, what it would be by mere reflection of light received from the sun. A drawing after Mr. Browning was published in the fifth volume of the "Student and Intellectual Observer," showing a broad, full, yellow equatorial belt; also broad belts of purplish brown edged with narrower yellow bands above and below it, and curious white patches in the upper dark belt. The polar belts were purplish and olive. The appearance and disappearance of these remarkable belts indicated great physical changes, and it is to be regretted that spectroscopes could not afford so much information as was hoped for. The planet, though appearing much brighter than any star, gives, according to Mr. Browning, a spectrum fainter than that of a star of the second magnitude. It is the size of the planet and his nearness, as compared with the distance of any fixed star, that make him such a brilliant object. The size of a luminous body greatly affects our estimation of the intensity of its light. Mr. Huggins, at the time mentioned, discovered some dark lines in the Jovian spectrum not belonging to the solar spectrum, and probably resulting from the absorptive action of the planet's atmosphere. He also pointed out that the remarkable yellow color had been seen some years before. Quite recently Mr. Huggins has been employing his large reflector to take photographic spectra of the planet, and he informs the writer that "from G to O in the outer violet there is no sensible modification, either in addition or absence of lines, of the solar spectrum." This is curious, as Jupiter has exhibited a good deal of primrose tint, with orange-brown belts and a big orange-brown spot.
A telescopic view of Jupiter usually exhibits some dark belts, occupying a zone of considerable breadth, on either side of the planet's equator, with less conspicuous markings nearer the polar regions. It is also common to find various-shaped patches brighter than the rest. Sometimes the general pattern formed by these markings lasts for months with little visible alteration. At other times a few min-
