One more mighty chasm of nine hundred millions of miles, for the same distance which separates the pathway of Saturn from the pathway of Uranus, separates also the pathway of Uranus from the pathway of Neptune. Cold, and dark, and dreary indeed seems to us the orbit on which this banished member of our family circle creeps round the sun, in the course of one hundred and sixty-five years, at the sluggish rate of three miles a second. On the planet Saturn, the quantity of light and heat received from the sun is not much more than a hundredth part of that which we are accustomed to receive on earth. But by the time we reach Neptune, the great sun has faded and shrunk in the distance until to our eyes he looks only like an exceedingly brilliant and dazzling star. We know little of this far-off brother, Neptune, except that he is rather larger than Uranus, being one hundred and five times as big as the earth; that he has at least one moon; and also that, like Uranus, he is made of materials lighter than those of earth, but heavier than those of Jupiter or Saturn. After all, it is no easy matter to gain clear ideas as to sizes and distances from mere statements of “so many miles in diameter,” and “so many millions of miles away.” A “million miles” carries to the mind a very dim notion of the actual reality. Now if we can in imagination bring down all the members of the Solar System to a small size, keeping always the same proportions, we may find it a help. “Keeping the same proportions” means that all must be lessened alike, all must be altered in the same degree. Whatever the supposed size of the earth may be, Venus must be still about the same size as the earth, Saturn seven hundred times as large, and so on. Also, whatever the distance of the earth from the sun, in miles, or yards, or inches, Mercury must still be one-third as far, Jupiter still five times as far, and thus with the rest. First, as to size alone. Suppose the earth is represented by a small globe, exactly three inches in diameter. It will be a very small globe. Not only men and houses, but mountains, valleys, seas, will all have to be reduced to so minute a size, as to be quite invisible to the naked eye. Fairly to picture the other members of the Solar System, in due proportion, you will have them as follows: Mercury and Mars will be balls smaller than the earth, and Venus nearly the same size of the earth. Uranus and Neptune will be each somewhere about a foot in diameter. Saturn will be twenty-eight inches and Jupiter thirty-two inches in diameter. The sun will be a huge dazzling globe, _twenty-six feet_ in diameter. No wonder he weighs seven hundred and fifty times as much as all his planets put together. Next let us picture the system more exactly on another and smaller scale. First, think of the sun as a brilliant globe, about nine feet, or three yards, in diameter, floating in space.