The finder can be used for many purposes, and it is a wonderful aid in making out in the sky the path of the stars, Sun, Moon and planets, and when they rise and set. In fact, it is a complete observatory on a small scale. Its cost is only $5.00. APPENDIX N THE ELLIS SEASONAL TWILIGHT CHART A useful chart, designed by Miss E. Rebecca Ellis, of Wellesley College, Wellesley, Mass. It makes clear the changes in the lengths of the day, the phenomena of the seasons, etc. Its price is $1.00. APPENDIX O THE CAMP FIRE SKY MAP This map, prepared by Prof. R. S. Dugan of Princeton University, shows the constellations as far south as the Southern Cross and is adjustable for the time of night, date, and for the latitude. Full instructions are given for its use. It is used in many schools and colleges. It is sold by the Camp Fire Stores Co., price 19 cents. DEFINITIONS OF SOME WORDS AND TERMS USED IN THIS BOOK =Action.= The way in which a thing works. =Affect.= To act upon; to change; to be moved or influenced by. =Almanac.= A pamphlet or book containing tables showing the days of the year; also the time the Sun and Moon rise and set; the conjunctions, eclipses and other information concerning the things in the sky. The word almanac is supposed to be derived from the Arabic article _al_ and the verb _manac_, which means to count. =Angular measurements.= See Appendix B. =Aphelion.= The point where a planet or a comet is farthest away from the sun. =Apparent.= To seem real. The daily motion of the Sun round the Earth is only apparent, for we know it is the Earth which turns round on its axis instead. =Arc.= See Appendix B. =Arc of circle.= See Appendix B. =Aspect.= (1) Any curious appearance of an object, especially if the object changes in appearance. (2)The figure formed by a planet with the stars of the constellation which it is in. =Astrologer.= One who forecasts the life of a person on the supposition that the stars control it. =Astronomer.= One who is skilled in seeing the stars and who knows them. =Atom.= A very small particle of matter. See Molecule; Matter. =Attract.= To pull toward. The attraction of the Sun and the Earth for each other is due to gravitation. =Attraction.= A force which pulls one body to another. =Attraction of Gravitation.= A force which pulls all bodies to each other. =Auditory nerve.= A nerve that carries the impressions of sound which reach the ear to the brain.