The stars just mentioned belong to the comparatively young stellar bodies, while the Sun in common with other yellow stars is considerably older. Correlated with their age is undoubtedly the greater mean density of the yellow stars. Around many of the young stars, for instance around the brilliant Altair, the principal member of the constellation Aquila, a gas shell of great expansion has been observed, usually consisting of hydrogen but frequently also of helium. These extensive gas appendages may be considered as a kind of atmosphere surrounding the stars in question. Their density is no doubt exceedingly small. Our own central orb, the Sun, is also endowed with rarefied gases outside of the luminous clouds. By their absorption of light they cause the dark lines in the Sun’s spectrum, after their discoverer named Fraunhofer lines. The greatest height from the surface of the Sun is reached by hydrogen, mixed with a small quantity of helium and with a gas, unknown on Earth, which we call coronium because it has been observed in the Sun’s corona. These gases may be looked upon as the atmosphere of the Sun. Similar conditions obtain no doubt on the major planets, which possess a density not essentially different from that of the Sun. They have, moreover, practically the same period of revolution around their own axis, Jupiter 9.9 hours, Saturn 10.3, and Uranus (probably) 10.8 hours. Judging by their density, they are, in all probability, like the Sun, gaseous throughout except for the heavy cloud formations which appear to constitute the outer limit of these stellar bodies. Their interior, like that of the Sun, may contain comparatively sluggish gas-masses, as certain peculiar patches appear on their exterior, similar to the sunspots and persisting for long intervals, sometimes over a year. The best known example of the kind is the so-called red spot on Jupiter, which has remained since 1878, although it is not so pronounced now as during its early days (see Fig. 11). Characteristic for these planets are certain bands of a marked delineation and running parallel with the equator (see Figs. 11 and 12). They are caused by the rapid peripheral motion of these planets, with Jupiter 28 and with Saturn 24 times that of the Earth. [Illustration: Fig. 11. The planet Jupiter in 1909 in Mercator’s projection by F. le Coultre of Geneva. The “red spot” over which the clouds are dispersed, is found at 355° Long. and 20° S. Lat. in the outcurving of the dark band. South direction is upward, as on all pictures obtained with astronomical tubes. ]