Εικόνες σελίδας
PDF
Ηλεκτρ. έκδοση

Greenwich chronometer when the sun is on the meridian; what is the ship's longitude ?

8. The longitude of Honolulu is 157° 52' W., and the longitude of Sydney, Australia, is 151° 11' E.; when it is 6 o'clock a. m. on Saturday at Honolulu, what is the hour and day of the week at Sydney?

INTERNATIONAL DATE LINE

224. The International Date Line is the imaginary line, agreed upon by civilized nations, as the line which separates the lands in the Pacific Ocean where American date is kept from those where Asiatic date is kept. Navigators generally use the 180th meridian, but the date line varies slightly from this meridian. In passing through Bering Strait it bends to the east of the 180th meridian, and in avoiding the Aleutian Islands it reaches a point 10° west of the meridian. From a point about go to a point about 50° south of the equator it lies a little to the east of the 180th meridian. (The remainder of its course coincides with that meridian.)

225. The day begins, by agreement, at midnight on this date line. Therefore if it is Sunday forenoon when a steamer going westward reaches the line, it becomes Monday forenoon the moment the line is passed. But in going eastward, upon reaching the line on Sunday forenoon, it becomes Saturday forenoon the moment the line is passed. Thus the day that is dropped in going westward is “picked up” again on the return trip.

STANDARD TIME

226. Primarily for the convenience of railway traffic, a uniform system of time-keeping, known as Standard Time,

was agreed upon in 1883 by the principal railroad companies of the United States and Canada. By this system, time meridians 15° apart have been established. The United States uses the meridians 75°, 90°, 105°, and 120° west from Greenwich. Places within the belt extending 71° east or west of a time meridian have the time of the time meridian. Therefore, the time between two places differs by whole hours, or not at all. The belts are named, beginning with the 75th meridian, as follows: Eastern Time, Central Time, Mountain Time, and Pacific Time.

227. Irregularities.-While the time meridians are exactly 15° apart, the belts using the several meridian times vary to suit the convenience of the railroads. This causes great irregularities. El Paso, Texas, has the same standard time as Savannah, yet there is a difference of 1 hr. 41 min. 30 sec. in local time. On the other hand, San Diego, California, has two hours later standard time than El Paso, although there is a difference of only 42 min. in local time.

Exercise XXVIII

1. The longitude of Buffalo is about 79° W. When it is noon in that city by standard time, what is the sun-time?

2. If a man travels from San Francisco to St. Louis, what change should he make in his watch?

3. Washington, D. C., is in longitude about 77° W. When it is 6 o'clock p. m. in that city by sun-time, what is the hour by a clock keeping standard time?

4. A man living in Galveston, Texas, observed that his clock, correct by sun-time, was 19 min. slower than the depot clock, correct by standard time. Find the longitude of Galveston.

5. Explain how the following information could reach the United States on Sunday, Feb. 28, 1904:

For two hours yesterday morning (Monday, Feb. 29, 1904), the Japanese squadron bombarded Port Arthur, injuring the Askold and Novik, and again damaging the Retvisan. The Japanese fleet is reported to have escaped injury.-Harper's Weekly.

IX. MEASURES OF TEMPERATURE

228. Temperature is usually measured by a thermometer constructed upon one of the following scales: (1) Fahrenheit (F.), boiling-point 212°, freezing-point 32o. (2) Centigrade (C.), boiling-point 100°, freezing-point 0°. (3) Réaumur (R.), boiling-point 80°, freezing-point 0°.

TABLE OF EQUIVALENTS. Boiling point F. C. R.

180° F.

80° R. of water

100° C. + 212° + 100°

+ 80°

1° “ =

[ocr errors]
[blocks in formation]

1. +86° F. corresponds to what readings on C. and R.? (1) 86° F. 32° F. = 54° F. = num. of degrees above freezing. (2) 1° F. ° C. = *° R. (3) 54° F.

54 x C. 54° R. (4) 54° F.

30° C. 24° R. (5) 54° F. + 32° F. 86° F. .: 86° F. corresponds to 30° C. and 24° R.

[ocr errors]
[ocr errors]
[ocr errors]

f°R.

[ocr errors]
[ocr errors]
[ocr errors]

2. -4° F. corresponds to what readings on C. and R.? (1) – 4° F. 32° F. 36° F. = num. degrees below freezing. (2) 1° F. C. (3)

36° F. 36 x 50 C. - 36 x 4° R. (4) – 36° F. 20° C. - 16° R. (5) – 36° F. + 32° F. = – - 4° F. .. – 4° F. corresponds to – 20° C. and 16° R. 3. +24° R. corresponds to what readings on F. and C.? (1) 80° R.

180° F.

100° C.
(2) 1° R.

° C.
(3) 24° R. 24 x F. 24 x 0 C.
(4) .. 24° R.

30° C. (5) 54° F. + 32° F. .. + 24 R. corresponds to 86° F. and 30° C. 4. -10° C. corresponds to what readings on F. and R.?

(1) 100° C. - 180° F. = 80° R.
(2) 1° C.

R.
(3) – 10° C. 10 x ° F. - 10 x 1° R.
(4) – 10° C.

18° F. -8° R.
(5)

18° F. - 14° F.
- 10° C. corresponds to 14° F. and — 8° R.

54° F.

86° F.

[ocr errors]

32° F.

Exercise XXIX

1. C. reads 10° above zero; what are the readings of F. and R.?

2. The temperature of the room is 68° F. Find the temperature in C.; in R.

3. Lead melts at 335° C. Find its melting point in F.

4. Silver melts at 1040° C. Find its melting point in R.; in F.

5. On a certain day the temperature fell from 95° F. to 10° C. How many degrees R. did it fall?

X. THE METRIC SYSTEM

229. The Metric System of weights and measures is used by all scientific writers throughout the civilized world. It is employed in the affairs of everyday life by most nations except the United States and Great Britain.

NOTE.—The Metric System was originated by the French. Two

surveyors, Delambre and Méchain, measured an arc of the meridian from Dunkirk, France, to Barcelona, Spain (a distance of about 10 degrees). From this they computed the distance from the equator to the pole. The quadrant thus obtained was divided into ten million equal parts; one part was made the base of the system, and was called a meter. All measures are derived from the meter. The system was adopted by France in 1840, and legalized in the United States in 1868.

230. The meter (Greek metron, measure) is the unit of length, and is 39.37043 inches long.

The multiples and submultiples of the meter and of

the units derived from it are based on the decimal

scale. The multiple units are designated by Greek prefixes

They are: deka (10), hekto (100), kilo (1000), and myria (10000). The submultiple units are designated by Latin prefixes. They are: deci (.1),

centi (.01), and milli (.001). An abbreviation of a submultiple begins with a small

letter, while an abbreviation of a multiple begins with

a capital letter. Many of the denominations given in the tables are not

in common use. Those usually employed in business or science are printed in bold-faced type.

« ΠροηγούμενηΣυνέχεια »