167.—Ruled glass in transit instrument 162 168.—The time ball 164 169.—Receiving time signals by wireless 165 170.—The zodiac as invented by the ancients 167 171.—The zodiac as we know it today 167 172.—Constellations and signs of the zodiac 170 173.—Cardboard zodiac 171 174.—Constellations of zodiac in circle 172 175.—Constellations of Aries the Ram 174 176.—Constellations of the Lion and Big Dipper 177 177.—Constellations of Virgo the Virgin 179 178.—Libra, Lion, Scorpio, Virgo 179 179.—Lyra, Aquila, Capricornus 181 180.—Camera pointing to North Star 186 181.—Star trails 187 182.—Boy looking through prism at slit in cardboard 189 183.—Fraunhofer’s lines 190 184.—The spectroscope 191 185.—Geometrical figures 195 186.—Kullmer star finder 209 THE BOOK OF THE STARS CHAPTER I HOW TO FIND THE NORTH STAR If you want to know something about the stars which will be helpful as well as entertaining, the first thing you should do is to be able to find the _North Star_. The North Star is taken as a starting point in the sky for two very good reasons: first, of all the thousands of stars which the eye can see, it moves the least; and second, it is _north_ from any place on the Earth’s surface from which it can be seen. It must be plain then that this star is the most important one of all to us, for by its friendly light we can easily tell the points of the compass, though we may be lost in an unknown land or shipwrecked on a strange sea. That is, of course, we can easily find the points of the compass if we have first learned how to find the North Star. =How to Make a Star Finder.=—To find the North Star for the first time is a very easy matter if the simple directions given below for making and using a star chart, or star finder, are followed. Get a smooth pine board, about 16 inches wide, 20 inches long and ⅞ inch thick; make two cleats of wood, each of which is 1 inch wide, 12 inches long and ½ inch thick, and screw these to the board near the ends and on the same side, to prevent the board from warping, as shown in Fig. 1. If a drawing board of any size is at hand, it will serve the purpose just as well as a homemade board.