Suppose we lay eight marbles around a large marble placed on top of a table and in the center. This means that all the marbles lie in the same plane which is the top of the table, as shown in Fig. 60. The planets are all arranged round the Sun, as shown in Fig. 61, just the same as if they were all placed on a big, level board or table top. If we draw a picture of the plane view of the planets (Fig. 60) and the top view of the planets (Fig. 61) together, we shall have a picture of the _solar system_, as the Sun and all of his planets are called, as shown in Fig 62. From these pictures you will see that the planets are not arranged, in distance from the Sun, in order of size. [Illustration: FIG. 62.—SOLAR SYSTEM IN PERSPECTIVE.] To remember the arrangement of these planets in their relation to the Sun commit to memory this simple sentence: _Men Very Early Made Jars Serve Useful Needs._ As the first letter of each of the above words is the same as the first letter of a planet, you will be able to instantly recall the proper place of any one of them. [Illustration: FIG. 63.—EGG SHELL ON PLATE.] =How the Planets Are Held in Space.=—If you will take an ordinary dinner plate and half an eggshell, and give the eggshell a slight spin on the rim of the plate—the rim should be slightly moistened—you will find that by tilting the plate a trifle the eggshell will revolve in two directions; first, it will spin round on its own axis, and second, it will travel round the rim of the plate, which we will call its orbit, as shown in Fig. 63. This double motion of the eggshell is exactly like the double motion of a planet—each one turns on his own axis and each travels round the Sun in its own orbit; moreover, all the planets travel round the Sun in the same direction, the nearest planets taking the shortest time to complete the circle or orbit, while those farthest away take the longest time to go round their orbits just as we might expect them to do. In the beginning of things the planets were a part of the Sun, as we shall see further on, and when they were thrown off by him they spun round their own axes, and they continued to spin round their axes just as a ball continues to do so after it has left the pitcher’s hand. The tendency to fly off at a tangent which every particle of a rotating body feels is called centrifugal force. Now, no one knows what centrifugal force is, but how it acts is very well known, and you can find out for yourself by making the following experiment. [Illustration: FIG. 64.—BOY THROWING STONE TO ILLUSTRATE CENTRIFUGAL FORCE.] Take a stone and tie one end of a string to it; now swing the stone round in a circle; if the string should break, or you should let it go accidentally (on purpose) the stone will shoot off at a _tangent_, that is in a line away from the circle in which it was swinging, as shown in Fig. 64.