1. What is the difference in time of two places if the difference in longitude is 15°? 30°? 60°? 90°?

2. State a rule for finding the difference in time when the difference in longitude is known.

3. What is the difference in longitude between two places if the difference in time is 1 hour? 3 hours? 24 hours? 4. State a rule for finding the difference in longitude, when the difference in time is known.

5. When it is noon here, what time is at it a place 15° east of here? 30° west? 120° west? 90° east? 45° east? 15° 30' west? 30° 15' east?

6. How far apart are A and D? 7. How far apart are B and F? 8. How far apart are A and C? 9. How far apart are C and G? 10. How far apart are B and C? 11. How far apart are D and G?

How was it found? How was it found? How was it found? How was it found? How was it found? How was it found? 12. State a rule for finding the difference in longitude between two places when both are in east longitude? When both are in west longitude? When one is in east and the other in west longitude?

Find the difference in longitude between places situated at the following meridians:

1. When it is 2 P.M. at A, 60° west longitude, what time is it at B, 90° east longitude?

A. Solution by using chart:

Turn the hour dial until 2 P.M., the time at A coincides with 60° W., the longitude of A. Find 90° E., the longitude of B, and on the hour dial read the corresponding time.

When it is noon at Paris, what time is it at Boston?

One place being in east longitude and the other in west longitude, we add and find the difference to be 73° 23′ 52". Since 15° of longitude makes a difference of 1 hr. in time, and 15' of longitude makes a difference of 1 min. in time, we divide the difference in longitude by 15°, and find the difference in time to be 4 hr. 53 min. 35 sec. Since Boston is west of Paris, it must have earlier time, so we subtract 4 hr. 53 min. 35 sec. from 12 M. and find the time is 6 min. 25 sec. past 7 o'clock A.M.

When it is noon at New York, what is the solar time of:

10. When it is 3 P.M. at New York, what time is it in New Orleans?

11. When it is noon at Canton, what time is it at Washington?

12. When it is 6 A.M. at Chicago, what time is it at Rome?

13. When it is 9 A.M. at C, 120° W., it is 12 м. at D. Find the longitude of D.

A. Turn the hour dial until 9 A.M. coincides with 120° W., Find 12 M. and read the longitude on the corresponding dial.

B. 12 hr. 9 hr. 3 hr.

=

=

45°

3 × 15° 120° 45° 75° w.

=

First find the difference in time. Since 1 hr. in time makes a difference of 15°, we multiply 15° by 3 and find the difference in longitude is 45°. Since the time at D is later than the time at C, it must be east of it. When we are in west longitude and travel east, we are moving toward the prime meridian, and therefore subtract 45° from 120°.

14. When it is noon at Paris, what is the time at St. Petersburg, 30° 16′ E?

When it is 10 o'clock A.M. at Philadelphia, 75° 10', it is
What is the longitude of Paris?

10 min. past 3 P.M. at Paris.

15 hr. 10 min. 77° 10 hr.

5 hr. 10 min.

75°

2°

30'

10'

20' E.

3 P.M. is the 15th hour of the day. The difference in time is 5 hr. 10 min., which corresponds to 77° 30' difference in longitude. Since Paris has later time than Philadelphia it must be 77° 30' east of it. Since the prime meridian is only 75° 10' east of Philadelphia, then Paris must be the difference between 77° 30′ and 75° 10' east of the prime meridian.

1. A and B sailed together from New York. A kept his watch by New York time and B set his by the sun every day. In a few days the watches were 2 hr. 16 min. apart. Whose watch was the faster? In what longitude were they?

2. The longitude of Jerusalem is 35° 32′ E. When it is 7.30 A.M. at New York, what time is it at Jerusalem?

3. What change must a person make in his watch in going from Washington to Paris?

4. A is 45° 10' east of B. What time is it at B, when it is 6 o'clock P.M. at A?

5. When it is noon at Greenwich it is 5 hr. 50 min. 26 sec. earlier at another place. From the table of longitudes, find the name of the other place.

6. Suppose an account of an accident, that happened in Manila 120° E. at 5 A.M. Wednesday morning, was sent to New York with only a loss of one hour in transmission, at what time would it reach New York?

7. At what time will quotations of the stock exchange in Paris reach New York, if cabled at 1 P.M.?

8. A ship in distress reports by wireless telegraph that she is in longitude 45° 30' west. If the message was sent at 10 A.M., when could the Boston station catch the message?

9. Allowing no time for transmission when could the New York papers receive dispatches sent at noon from Canton? Rome? Manila?

1. The difference in time between all places caused such inconvenience to the railroads and persons traveling that in November, 1883, the railroads of the United States and Canada adopted what is called Standard Time.

2. Four meridians were chosen, 15° apart, as central meridans. These are the 75°th, 90°th, 105 th, 120°th. It was intended that all places 71° on either side of these meridians should form a belt, but as a matter of fact the railroads found it necessary to change time at some convenient point. The result is very irregular boundaries for the belts.

3. These time belts are called Eastern, Central, Mountain, and Pacific.

4. When it is noon in the Central belt, what time is it in the Eastern? Mountain? Pacific?