We remark here a great diversity in regard to magnitude,--a diversity which does not appear to be subject to any definite law. While Venus, an inferior planet, is nine tenths as large as the earth, Mars, a superior planet, is only one seventh, while Jupiter is twelve hundred and eighty-one times as large. Although several of the planets, when nearest to us, appear brilliant and large, when compared with most of the fixed stars, yet the angle which they subtend is very small,--that of Venus, the greatest of all, never exceeding about one minute, which is less than one thirtieth the apparent diameter of the sun or moon. Jupiter, also, by his superior brightness, sometimes makes a striking figure among the stars; yet his greatest apparent diameter is less than one fortieth that of the sun. _Periodic Times_. Mercury revolves around the sun in nearly 3 months. Venus, " " " " 7-1/2 " Earth, " " " " 1 year. Mars, " " " " 2 years. Ceres, " " " " 4-2/3 " Jupiter, " " " " 12 " Saturn, " " " " 29 " Uranus, " " " " 84 " From this view, it appears that the planets nearest the sun move most rapidly. Thus, Mercury performs nearly three hundred and fifty revolutions while Uranus performs one. The apparent progress of the most distant planets around the sun is exceedingly slow. Uranus advances only a little more than four degrees in a whole year; so that we find this planet occupying the same sign, and of course remaining nearly in the same part of the heavens, for several years in succession. After this comparative view of the planets in general, let us now look at them individually; and first, of the inferior planets, Mercury and Venus.