Here is a curious circumstance: on account of the difference of rotation, the Jovian year comprises 87 more (Jovian) days at the equator than it does in the subtropical zone. If it were the same on our globe, the inhabitants of the Congo, Colombia, Borneo, and Sumatra would have a day more in their year (and even five in four years) than those of Senegal, the Antilles, Siam, or India, a difference of 125 days per century! It would be difficult to keep their calendars in agreement. There are seven or eight kinds of currents between the equator and the poles, so that one can say of Jupiter, as of the Sun, that it does not turn in one piece. And those speeds themselves vary with the years. In the southern tropical zone there is a curious spot which has been followed with some interest for fifty years. Although it is much larger than the Earth, it seems to float in the current. Constant observation shows its period of rotation to have been 9 hours 55 minutes 41 seconds in 1900 and 9 hours 55 minutes 39 seconds in 1906, and its period returned in 1913 to the figure of 1900. What is the nature of this floating spot? In 1890 its colour was red. It then gradually got paler, and then pink once more. Its shape was that of a long oval, measuring 26,000 miles in length, or more than three times the diameter of our globe. The current in which it floats has not the same period of rotation as the spot itself. The spot is pushed from west to east, and it has shifted 57 degrees in two years. Now, a degree on the globe of Jupiter in that latitude represents 720 miles. This Jovian formation has, therefore, been displaced 41,000 miles, or a distance more than five times the diameter of our planet. It is as if Australia were to detach itself from the bottom of the sea and float about on the surface of the Pacific Ocean! Does this oscillation, which we only see in plan, and not in elevation, indicate the formation of a satellite trying to disengage itself from its parent planet and not succeeding? It looks as if there were on this giant world of Jupiter no surface at all, but irregular aerial layers one over the other, and full of clouds. The temperature must be very high, and enormous masses of vapour are formed, to wrestle in prodigious storms. Though mythology is of no importance here, it is evident that Jupiter is indeed the god of thunder-storms. Jupiter is a world in the making, a sun which has lost its light, but not its heat. Its density, nearly equal to that of the Sun, is barely greater than that of water. A globe of vapour varied by mountains of clouds, impalpable Himalayas, aerial Alps in convulsions, fluid and constantly agitated Pyrenees! Its colossal bulk has prevented its cooling as fast as our Earth, and it will no doubt take tens of hundreds of millions of years to arrive at a temperature fit for inhabitants. In all probability there is nobody yet on Jupiter, neither men nor animals nor plants. This immense world is in its primordial