LONGITUDE AND TIME 209. Longitude is the distance east or west from an established point or meridian on the earth's surface. Nations usually fix their own capital or national observatory as the point from which to measure longitude, but in the United States it is quite customary to reckon from the observatory at Greenwich, England. 210. Standard Time is the sun time of some selected meridian of longitude. Solar Time is the sun time, mid-day occurring at a given place when the sun reaches the meridian of that place, thus, there is a different time for every meridian. The standard time was adopted to avoid the necessary confusion caused to travelers and others by the difference of time. Railroads and many cities and towns have adopted standard time. In the United States eastern standard time is the sun time of the meridian 75° west of Greenwich; central standard time, 90°; mountain standard time, 105°; western (Pacific) standard time, 120°. The standard time is one hour earlier in the day, in each successive belt toward the west; and one hour later in the day, in each successive belt toward the east. Thus, when it is 11 a. m. in the Eastern belt-71° on each side of the 75th meridian—it is 10 a. m. in the Central belt, 9 a. m. in the Mountain belt, 8 a. m. in the Western belt. Every circle, great or small, may be considered as divided. into 360 equal parts called degrees. Since the earth turns on its axis once in 24 hours, a point on the earth's surface will describe a circumference (360°) in 24 hours; in 1 hr., the point would describe 24 of 360° or 15°; in 1 min., the point would describe ¿ of 15° or 15'; in 1 sec., the point would describe 15". Therefore we have the following: of 15′′ or TABLE OF COMPARISON BETWEEN LONGITUDE AND TIME 15° of longitude 1 hour of time. 15' of longitude 1 min. of time. The following table showing the longitude of important cities of the world east or west from Greenwich, England, will be used in the solution of the problems: 1. The difference in longitude between two places is 18° 25' 30". What is the difference in time? SOLUTION 60 15)18° 25′ 30" 1 13 42 EXPLANATION. By reference to the table of comparison on the previous page we see that 15° equal an hour of time, 15′ equal 1 min. of time and 15′′ equal 1 second of time. Therefore 18° 25′ 30′′ will be equal to as many hours, minutes and seconds as 15 is contained in them, and dividing according to the rules for division of Compound Numbers we have as a result 1 hr. 13 min. 42 sec. From the foregoing we have the following: To Change Longitude to Time a. Divide the longitude by 15 according to the rule for division of Compound Numbers and the result will be time. Since the reverse of division is multplication, we may reduce time to longitude by the following: To Change Time to Longitude a. Multiply the time by 15 according to the rule for multiplication of Compound Numbers and the result will be longitude. NOTE. If one place be in east, and the other in west longitude, the difference of longitude is found by adding them, and if the sum be greater than 180°, it must be subtracted from 360°. 2. The difference of longitude between two places is 30°. What is the difference of time? 3. The difference of longitude between two cities is 16° 34'. What is the difference of time? 4. The difference of longitude between New York and Chicago is 13° 11'. What is the difference in time? 5. The difference of time between two places is 2 hr. 30 min. What is the difference of longitude? 6. The difference of longitude between London and Washington is 77° 0′ 15′′. What is the difference in time? 7. What is the difference in time between Portland, Me., and New Orleans? 8. What is the difference of time between Richmond, Va., and Des Moines, Ia.? 9. What is the difference in time between Detroit, Mich., and San Francisco, Cal.? 10. What is the difference in time between Nashville, Tenn., and Omaha, Neb.? 11. What is the difference in time between New Haven, Conn., and Denver, Colo.? 12. What is the difference in time between New York and Sitka, Alaska? 13. What is the difference in time between Rio Janeiro, Brazil, and Honolulu, Sandwich Islands? 14. What is the difference in time between Rome, Italy, and Boston, Mass.? 15. When it is noon at Charleston, S. C., what is the time at Indianapolis, Ind.? NOTE. Since Charleston is east of Indianapolis, subtract the difference of time. 16. When it is 2 p. m. at St. Louis, Mo., what is the time at Philadelphia, Pa.? NOTE. Since St. Louis is west of Philadelphia, add the difference of time to 2 p. m. 17. When it is noon at Chicago what is the time at Rome, Italy? NOTE. Since Chicago is west and Rome east of the prime meridian, the difference between their longitudes is found by taking the sum of their longitudes. Since Rome is east of Chicago, the difference of time is added to the time of Chicago to find the time at Rome. 18. When it is 1 p. m. at Omaha what is the time at Paris, France? 19. What is the time of day at Berlin when it is 2 p. m. at New York? 20. When it is midnight at Boston what is the time at Austin, Texas? 21. What is the time of day at Washington when it is 28 min. past 10 a. m. at Chicago? 22. St. Petersburg is east longitude and St. Louis is west longitude. When it is 1 a. m. at St. Petersburg, what is the time at St. Louis? 23. When it is 1 a. m. on Wednesday at Washington what is the time at Bombay? When it is 10 min. past 2 a. m. on Sunday at Bombay what is the time at Washington? 211. The International Date Line is an imaginary line, in crossing which navigators must either add or subtract a day in order to make their calendar correspond to that of the inhabitants of the adjacent islands. Given the time of day and longitude of one place and the longitude of another, and the time of day of the latter is easily. found but to find the correct day of the month is not always so easy. For this purpose a knowledge of the "International Date Line," a cut of which is given on the following page is indispensable. Travelers in going round the earth to the west find themselves a day behind the calendar and when going east, a day ahead, irrespective of the time required to make the trip. Starting from somewhere in Asia the world has been peopled by some going east and some going west. These tides, as it were, of people met in the Pacific ocean, Asia and a few islands along the coast being peopled by those coming from the west and America with the islands in the eastern Pacific by those coming from the east. Each branch brought its own time and when they met they must necessarily differ by a full day. The "International Date Line" represents where they met and hence marks the division between the two kinds of time. On one side of the line it is |