60. Q. What is all that we ordinarily see with the eye or telescope of the sun? A. The shining surface called the photosphere on which the cromosphere rests. 61. Q. What is the diameter of the photosphere, or the visible and measurable part of the sun? A. Eight hundred and sixty thousand miles. 62. Q. How many globes like the earth would it require to measure the sun’s diameter? A. One hundred and eight. 63. Q. What is the volume of the sun as compared with that of the earth? A. It is 1,245,000 times greater. 64. Q. What is the density of the sun as compared with that of the earth? A. It is only one-fourth as great. 65. Q. What is the mass of the sun as compared with that of all the planets, asteroids, and satellites of the solar system put together? A. It is seven hundred times as great. 66. Q. What are some of the opinions as to the surface of the sun? A. That it is hot beyond all estimate is indubitable. Whether it is solid or gaseous we are not sure. 67. Q. What on the surface of the sun have been objects of earnest and almost hourly study on the part of eminent astronomers for years? A. The spots. 68. Q. To what must the speed of the orbital revolution of the planets be proportioned? A. To the distance from the sun. 69. Q. What is the orbital speed of Mercury, and what that of Neptune? A. That of Mercury is about twenty-nine and a half miles in a second, and that of Neptune about three and one-third miles a second, or nearly nine times as slow. 70. Q. How do the periods of the axial revolution, which determine the length of the day, vary with the four planets nearest the sun? A. They vary only half an hour from that of the earth. 71. Q. In what time do Jupiter and Saturn revolve? A. In ten and ten and a quarter hours respectively. 72. Q. What is the density of Jupiter and Saturn as compared with the earth? A. That of Jupiter is about one-fourth and that of Saturn is about one-eighth that of the earth. 73. Q. How much less is the polar diameter of Jupiter than the equatorial? A. Five thousand miles. 74. Q. If we represent the sun by a globe two feet in diameter, how could we represent the comparative size of the five planets nearest the sun? A. Vulcan and Mercury by mustard seeds, Venus and Earth by peas, and Mars by one half the size. 75. Q. How could the comparative size of the other planets be represented? A. Asteroids, by the motes in a sunbeam; Jupiter, by a small-sized orange; Saturn, by a smaller one; Uranus, by a cherry; and Neptune, by one a little larger. 76. Q. Applying the principle that attraction is in proportion to the mass, what would a man weighing one hundred and fifty pounds on the earth weigh on Jupiter, and what on Mars? A. On Jupiter he would weigh three hundred and ninety-six pounds, and on Mars only fifty-eight pounds. 77. Q. How are the seasons of the planets caused? A. By the inclination of its axis to the plane of its orbit.