Water was found on mars, but not not before it, like earth, was subjected to fire. All the planets are composed of a light substance much of the same kind as fire. But, so vast is their size that fire is not so quick and powerful there as on earth. Many years ago it was supposed that Venus had a different light from the sun; we now know that the apparent difference is caused by a difference in our own motions as compared with the planets. The great discovery that there are other systems of sun and stars in the sky was made by Galileo, and is called the Copernican system. The earth is a planet, and is in company with others as large as our earth and even larger, all moving round a sun like our own sun. The moon is covered with fine seas and mountains. Saturn is a planet so large that it can take six years to go round the sun. The sun is the center of our system and the greater luminary that lights the night. Venus is to the earth as our moon is to the earth. Mars is a planet very like the earth. It was thought that there was but one moon, but Galileo made a great discovery. He found that there were two moons, one the moon that we call Diana, and the other is named after his friend Callisto. The moon changes its shape very often, that is, some of its shape. The moon and the earth are in a good position to the sun; they almost complete a circle round him, and, what is most remarkable, the moon goes round the earth once every twenty-seven days. This is the reason of the changes in the moon's shape. The moon revolves round the earth very slowly; but it revolves round the sun much faster; it takes about twenty-seven days to go round the sun, and in a month's time the moon goes round once more. The moon is nearer to us when its changes are larger. As it goes round the earth, on the part where it is nearest the earth we call the moon new, when it comes round to that part on which it is farthest away, it is called old. As the moon is nearer to the earth when it is new, the parts of it which are nearest to us will then appear larger, as well as its surface. The moons of Jupiter and Saturn are so much larger than the moon that we cannot see them with a telescope; they would be much brighter than our moon and stars if they were not so far away. Jupiter has five moons, Saturn four. These moons do not change their shape at all; they are always the same, and in shape they are much like our moon. Saturn has two rings, and there are probably moons in them like our own, for Saturn's rings are now very plain. The change in the moon's shape is only a shadow thrown on the surface of the moon from a group of mountains upon the earth, or a shadow thrown from the earth. We say that the moon changes her shape, but we must understand that she does not change, but that the shadows cast by the earth on the moon are distorted. We do not see any sign of animal life on the moon; the sun is too powerful there for the existence of any such thing. Mercury is nearest to the sun, and that planet does not change its shape, because it is too small. Mercury revolves round the sun in three hundred and sixty-five days, or more than three years. When we use the word "year" we do not know how many days a year has, but the word year means a year in the time of the moon. We know that the moon takes about one month to go round the earth, but the sun takes nearly thirty-three and a quarter years, and this time is called one _sidereal year_. This is a year as measured on our earth, but Mercury revolves round the sun once in three hundred and sixty-five days, and in this time passes a whole year in the sky. Mercury is only thirty-three days long, or a third of a month, as measured on our earth. The sun does not cast a shadow, so we do not see the dark side of Mercury, which is always facing the sun. Mars, after the moon, is next to the earth in distance from the sun, and is also so near to us that we see him easily, and with his four small moons all in company, and all revolving round him. The change of the moon's shape is caused by the shadow of the earth. It seems as if the earth cast a shadow on the moon, but the explanation is that we are so far from the moon that it seems smaller. The shadow of the earth casts a different shape than if the moon were farther from us. With a very large glass you can see one of the large moons of Mars, called Deimos and Phobos, but they are much farther away from us than we are from Mars. You see one of these moons in less than half an hour; then you see the whole of one of them in about four hours, and all in a little more than four hours you can see the whole surface of the moon, which is so much larger. There is probably life on Mars, and on some other planets; as the sun is so much larger than the earth, the planets are so much larger than the earth, so that our earth is only a tiny speck in comparison. We see from these facts that we are not so important in the universe. In a way we are of no account at all in the great scheme of things. But that does not trouble us much. When we look round the universe we cannot but be filled with admiration and wonder. How to Read a Dial A dial is a device for showing the time of day by day or night by night. Dials are made of stones, stone or marble figures cut in the shape of spirals, circles, or ovals. Dials are round, square, octagonal, and oval. Round dials are divided into six spaces, each marking ten minutes of an hour; square dials are divided into four spaces each marking five minutes of an hour, and octagonal dials are divided into eight spaces each marking twelve minutes of an hour. All of these have an outer circle for the full day, and an inner circle for the night. The ancient Greeks used a round dial, and these figures are used now to tell the time of day in astronomical observatories. The Romans used a ring of thirty dials in each wall; the first at the north signified the day and hour; the last at the south signified the day and hour. In the center of this ring is an opening, through which the sun, moon, or other celestial object could be seen. [Illustration: FIG. 1] Fig. 1 shows how to draw a round dial. A is a circle which is divided into twelve parts by diameters D, D, and the spaces at E, E; B is a circle divided into four parts by diameters G, G. The dial is to be divided in the same way into twelve parts, or divisions. We can find out how many there are by taking 12 or 24 times four as the number of divisions. For example, 24 is 12 times 4, and 12 is 4 times 3, so the number of divisions is four. It is a matter of choice how to divide the circle into the divisions, but the following is an easy and convenient method of marking the hours on the circle: We will call the center of the dial K. Then we make divisions from K to K through D, D, and so on in both directions. The points where the diameters cross are denoted by S, S, S', S'', and as these are equally distant from K, K, they will mark divisions of the hours. All the points of intersection of a circle and a diameter are equally distant from the center of the circle. Dial Rings, How to Draw Them Fig. 2 shows the same dial with the inner circle turned. We will first show how to draw the parts which are outside the dial. Draw a dotted line from B to B', and we have a half circle for the night. Similarly B' is the point of division for the day. Now draw another dotted line from S' to O, and this shows us the point of division for the 12 hours. Here O is the first hour, and this we may call the 12th, as 12 is four times 3; then draw another dotted line from S'' to S'''. This shows us the point of division for the 24 hours. Here O is the last hour, as this 24th hour can be measured from O by means of 24 and S'''. And we shall call this hour the 24th hour. [Illustration: FIG. 2] When