When you look up into the sky from the Earth you see the clouds moving and changing their shapes slowly. But if you could go quite near you would find their changes to be really very quick. And just so--only very much more so--at the vast distance of Jupiter we see movements which to us seem tiny and slow, yet which we believe to mean there, on the spot, the wildest rushings of heated clouds hither and thither. No storms on the Earth can be spoken of in the same breath with the terrific storms on Jupiter. And the question is--what brings this about? Our earthly tempests are caused by the heat of the Sun, but the Sun is so very far from Jupiter and yet the storms there are much more violent than any here. Do you remember being told that once upon a time, long, long ago, our Earth, now so cold and quiet a globe, was most likely a dazzling little Sun, and that she slowly cooled down from a Sun to a world? When she was a Sun she was fiercely hot and glowing gases played over her; and instead of solid ground and liquid seas there were only raging vapors, bright with their own heat. The Earth was larger then than now, for gases take up much more room than water and rocks and earth. Between those days and these our Earth must have passed through a _half-way_ stage. Suppose you have a lump of ice, and you wish to turn it into hot steam--how can you do it? Of course you must heat the ice, and then it will melt--not into steam, but into water. And when you have the water you can heat that again till it boils and goes off in steam--or, as we say, “it boils away.” Again, if you had steam and wished to turn it into ice, it would have to go through being water between the steam-state and the ice-state. So the water is a kind of half-way stage between ice and steam--between great cold and great heat. No doubt, our Earth, as she cooled, passed through a “half-way stage” too. She did not all at once become firm and cool. First she was a bright Sun, made of glowing gases. Then she was a half-sun, half-world: no longer shining, yet very hot indeed; no longer made of gases, but by no means solid. Then lastly she cooled down, as we now see her. These are, we suppose, three chief parts in the story or life of a heavenly body. Our Sun is in the early part--made of gases, exceedingly hot and bright. Our Earth is in the later part, cold and firm, and not shining! But Jupiter seems to be still in the middle part, in the half-way stage. He is very, very hot, yet not so hot as to give forth light of his own, for he shines by the Sun’s light. He is not any longer a great mass of gases, yet he seems to be very far from being solid and firm. The clouds which cover Jupiter, though not like the fiercely-glowing Sun-clouds, are yet very unlike our cool Earthly mists, and perhaps they may be at least as hot as the steam which pours from a boiling kettle.