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Longitude and Time-Table

For every hour of time there is a difference of 15° in longitude. " minute " " 15' " " second " " 15" " ८८ degree of longitude " 4 minutes in time. " minute " " 4 seconds " ८८ second " " 1-16 seconds " 360° - I revolution of the earth, or 1 day. 1440" = I " " " 1440 - 360 = 4 minutes, or 1 degree.

I Add difference of time for places east, and subtract it for places west of any given locality. The greatest circumference of the earth's surface is 24,930 miles. 1º of that circumference is 1-360th of that number, or 6914 miles. Hence a geographical or nautical mile is equal to 1' of the earth's greatest circumference, or a trifle more, the 1st mile and 49 rods. The following table exhibits the divisions of the circle as used by geographers, astronomers, surveyors, navigators, etc.: 60 seconds (") make 1 minute, marked ' 60 minutes make 1 degree, marked ° 30 degrees make I sign, marked sig. 90 degrees make I quadrant, marked quad.

I right angle, marked r. a. 4 quadrants or 12 signs make I circumference or circle, marked cir. EQUIVALENTS.

Q C S I 12 If I 360 60 = I = = 21,600 1,800 60 = = I = = 1,296,000. 108,000. 3,600. 60.

A full circle is 360°, 1½ circle is 180°, 14 circle is 90°, circle is 60°. The distance around a circle is called its circumference. The distance across its diameter, and any section of its circumference is called an arc. Geological Time. The divisions of time established by geologists are based upon the formations of strata and the advents of different forms of animal life. The history of the earth is divided into five "eras," seven "ages," twenty-two "periods," and the last two periods are subdivided into seven epochs. These divisions, proceeding from the fifth downward to the first, are as follows: Psychozoic era, age of man, human period, and recent epoch. Cenozoic era, or age of mammalsembracing the quaternary period, which comprehends the terrace. Champlain and glacial epochs, and the tertiary period, which comprehends the pliocene, miocene, and eocene epochs. Mesozoic, or middle era, the age of reptiles, the cretaceous, jurassic, and triassic periods. 2. Paleazoic era, the carboniferous age, or age of acrogens and amphibians; the Devonian age, or age of fishes; the silurian age, or age of invertebrates, or mollusks-the names of the fourteen periods into which these ages are divided are not in common use. 1. Archaean, or eozoic era; the archaean age, and the Huronian and Laurentian periods. Clocks. In the year 1000 A. C. the Arabs used the pendulum as a measure of time. A second calculated by the movement of a 39-inch pendulum is one with that motion, and the movement itself is a simple deflection of the combined motions of the earth in its orbit from east to west, and on its axis from west to east. The origin of clock work is involved in great obscurity. Notwithstanding the statements made by many writers that clocks, horologia, were in use so early as the ninth century, and that they were then invented by an archdeacon of Verona named Pacificus, there appears to be no clear evidence that they were machines at all resembling those which have been in use for the last five or six centuries. But it may be inferred from various allusions to horologia, and to their striking spontaneously, in the twelfth century, that genuine clocks existed then, though there is no surviving description of any one until the thirteenth century, when it appears that a horologium was sent by the Sultan of Egypt in 1232 to the Emperor Frederick II. It resembled a celestial globe, in which the sun, moon and planets moved, being impelled by weights and wheels, so that they pointed out the hours, day and night, with certainty. A clock was put up in a former clock-tower at Westminister with some great bells in 1288, out of a fine imposed on a corrupt chief-justice, and the motto, "Discite Justitian, Moniti," inscribed upon it. The bells were sold, or rather, so it is said, gambled away by Henry VIII. In 1292 one is mentioned in Canterbury Cathedral as costing £30; and another at St. Alban's, by P. Wallingford, the abbot, in 1326, is said to have been such as there was not in all Europe, showing various astronomical phenomena. A description of one in Dover Castle, with the date 1348 on it, was published in 1851, and the clock itself was exhibited going in the Scientific Exhibition in 1876. NOTES.