SUPPLEMENTARY MATERIALS 



193 



east of that meridian have afternoon and places west 

 have forenoon. Thus when it is twelve o'clock noon 

 in Minneapolis it is afternoon in New York City and 

 forenoon in Los Angeles. 



Since the earth rotates on its axis once in twenty- 

 four hours, it rotates 1/24 of 360 degrees, or 15 de- 

 grees, in one hour. If we wanted to keep our watches 

 and clocks accurately timed according to the earth's 

 rotation, we should have to set them back four min- 

 utes for every degree of longtitude we travel westward 

 or put them ahead four minutes for every degree 

 longitude we travel eastward. To avoid the confusion 

 this would cause in commerce and travel, standard 

 time was adopted in 1884. The country was divided 

 into four districts or time belts. The time in each 

 district was made one hour earlier than the district 

 to the east of it and an hour later than the district to 

 the west of it. These four times are called Eastern, 

 Central, Mountain, and Pacific Standard times. The 

 map in Figure 316 shows the time belts of the United 

 States. The 75th meridian, passing through Phila- 

 delphia, is the starting point. All places east and west 

 within a half hour of the local time of the 75th merid- 

 ian use the local time of this meridian. This is the 

 eastern time belt, and its time is known as Eastern 

 Standard Time. Going westward we find the central 

 time belt, the mountain time belt, and the Pacific time 

 belt, which have the local times of the 90th, 105th, and 

 120th meridians, respectively. It should be noticed 

 on the map that the boundaries of the different time 

 belts are not exactly on the meridians just mentioned. 

 The dividing lines are not straight, but are arranged 

 to correspond to division points of the railroads, thus 

 avoiding inconvenience in operating the railroads. 

 The same general plan is used now throughout prac- 

 tically the entire civilized world. 



REFERENCES FOR FURTHER STUDY 



Texts 



Caldwell and Curtis, Science for Today, Chaps. 17 and 18 

 Clement, Collister, and Thurston, Our Surroundings, Chap. 



11 

 Hunter and Whitman, Science in Our World of Progress, 



Unit 9 ; Science in Our Social Life, Unit 9 

 Lake, Harley, and Welton, Exploring the World of Science, 



UnitS 



Pieper and Beauchamp, Everyday Problems in Science, Unit 

 1 



Powers, Neuner, and Bruner, This Changing World, Chap. 4; 

 Man's Control of His Environment, Chap. 29 



Skilling, Tours through the World of Science, Tour 6 



Van Buskirk and Smith, The Science of Everyday Life, pp. 

 302-311 



Watkins and Bedell, General Science for Today, Chap. 10 



Webb and Beauchamp, Science by Observation and Experi- 

 ment, Unit 6 



Wood and Carpenter, Our Environment: How We Adapt 

 Ourselves to It, Topic 4; Our Environment: How We Use 

 and Control It, Topic 14 

 Special references 



Fabre, The Story Book of Science 

 Fabre, This Earth of Ours 

 Seeley, The Story of the Earth 

 Washburne, The Story of the Earth 



WHAT YOU SHOULD AIM TO ACQUIRE FROM 

 THIS STUDY 



1. A knowledge of the cause of the phases of the 

 moon. 



2. The cause of lunar and solar eclipses. 



3. The causes of ocean tides. 



4. The cause of day and night. 



5. The cause of the change of seasons. 



6. How time is kept. 



TEST OF MASTERY OF THE TOPIC 



In your notebook complete the statements, answer the 

 questions, and comply with the instructions. 



1. The phases of the moon are 



2. When the moon is at A (Fig. 310) its phase is spoken 

 of as 



3. When the moon is at D its phase is spoken of as 



4. The moon is in first quarter when it is at . _. 



5. The moon is at full when it is at 



6. The length of day on the moon is 

 length of night is . 



days and the 



7. The sun crosses the equator on 



and 



moon, and 



8. Lunar eclipses may occur only at . 

 solar eclipses only at . moon. 



9. Partial eclipses are caused by 



10. Show, by means of a diagram, how a solar eclipse 

 is total only for a small portion of the earth. 



11. Explain why days and nights are of unequal length 

 at different times of the year. 



12. On what dates are day and night of equal length ? 



13. Why do the seasons change? 



14. Why do we have our warmest weather in summer 

 even though we are farther from the sun than in the winter? 



SUPPLEMENTARY MATERIALS 



Reading suggestions 



Darrow, Masters of Science and Invention (Har- 



court) 



Gibson, Heroes of Science (Lippincott) 

 Collins, Th'e Boy Astronomer (Lothrop) 

 Proctor, The Young Folk's Book of the Heavens 



(Little) 

 Lewis, Astronomy for Young Folks (Duffield) 



Murphy, A Beginner's Star Book (Putnam) 

 MacPherson, The Romance of Modern Astronomy 



(Lippincott) 



MacPherson, Modern Astronomy (Oxford) 

 Rogers, Earth and Sky Every Child Should Know 



(Grosset) 



Serviss, Astronomy irith the Naked Eye (Harper) 

 Jeans, The Mysterious Universe (Macmillan) 



