We must now close our description of this lovely planet; but before doing so, let us add--or in some cases repeat--a few statistical facts as to the size and the dimensions of the planet and its orbit. The diameter of Venus is about 7,660 miles, and the planet shows no measurable departure from the globular form, though we can hardly doubt that its polar diameter must really be somewhat shorter than the equatorial diameter. This diameter is only about 258 miles less than that of the earth. The mass of Venus is about three-quarters of the mass of the earth; or if, as is more usual, we compare the mass of Venus with the sun, it is to be represented by the fraction 1 divided by 425,000. It is to be observed that the mass of Venus is not quite so great in comparison with its bulk as might have been expected. The density of this planet is about 0.850 of that of the earth. Venus would weigh 4.81 times as much as a globe of water of equal size. The gravitation at its surface will, to a slight extent, be less than the gravitation at the surface of the earth. A body here falls sixteen feet in a second; a body let fall at the surface of Venus would fall about three feet less. It seems not unlikely that the time of rotation of Venus may be equal to the period of its revolution around the sun. The orbit of Venus is remarkable for the close approach which it makes to a circle. The greatest distance of this planet from the sun does not exceed the least distance by one per cent. Its mean distance from the sun is about 67,000,000 miles, and the movement in the orbit amounts to a mean velocity of nearly 22 miles per second, the entire journey being accomplished in 224.70 days. CHAPTER IX. THE EARTH. The Earth is a great Globe--How the Size of the Earth is Measured--The Base Line--The Latitude found by the Elevation of the Pole--A Degree of the Meridian--The Earth not a Sphere--The Pendulum Experiment--Is the Motion of the Earth slow or fast?--Coincidence of the Axis of Rotation and the Axis of Figure--The Existence of Heat in the Earth--The Earth once in a Soft Condition--Effects of Centrifugal Force--Comparison with the Sun and Jupiter--The Protuberance of the Equator--The Weighing of the Earth--Comparison between the Weight of the Earth and an equal Globe of Water--Comparison of the Earth with a Leaden Globe--The Pendulum--Use of the Pendulum in Measuring the Intensity of Gravitation--The Principle of Isochronism--Shape of the Earth measured by the Pendulum.