SCALE-ascending, 60, 8, 16, 8; descending, 8, 16, 8, 60. MEASURE OF TIME. 299. Time is the measure of duration. The unit is the day, and the table is made up of its divisors and multiples. SCALE ascending, 60, 60, 24, 7; descending, 7, 24, 60, 60. NOTES.1. In most business transactions 30 days are called 1 month. 2. The civil day begins and ends at 12 o'clock, midnight. The astronomi cal day, used by astronomers in dating events, begins and ends at 12 o'clock, noon. The civil year is composed of civil days. BISSEXTILE OR LEAP YEAR. 300. The period of time required by the sun to pass from one vernal equinox to another, called the vernal or tropical year, is exactly 365 da. 5 h. 48 min. 49.7 sec. This is the true year, and it exceeds the common year by 5 h. 48 min. 49.7 sec. If 365 days be reckoned as 1 year, the time lost in the calendar will be The time thus lost in 4 years will lack only 44 min. 41.2 sec. of 1 entire day. Hence, If every fourth year be reckoned as leap year, the time gained in the calendar will be, In 4 yr., "100 66 44 min. 41.2 sec. 66 The time thus gained in 100 years will lack only 5 h. 22 min. 50 sec. of 1 day. Hence If every fourth year be reckoned as leap year, the centennial years excepted, the time lost in the calendar will be, The time thus lost in 400 years lacks only 2 h. 28 min. 40 sec. of 1 day. Hence If every fourth year be reckoned as leap year, 3 of every 4 centennial years excepted, the time gained in the calendar will be, The following rule for leap year will therefore render the calendar correct to within 1 day, for a period of 4000 years. I. Every year that is exactly divisible by 4 is a leap year, the centennial years excepted; the other years are common years. II. Every centennial year that is exactly divisible by 400 is a 'leap year; the other centennial years are common years. NOTES.-1. Julius Cæsar, the Roman Emperor, decreed that the year should consist of 365 days 6 hours; that the 6 hours should be disregarded for 3 successive years, and an entire day be added to every fourth year. This day was inserted in the calendar between the 24th and 25th days of February, and is called the intercalary day. As the Romans counted the days backward from the Orst day of the following month, the 24th of February was called by them sexto calendas Martii, the sixth before the calends of March. The intercalary day which followed this was called bis-sexto calendas Martii; hence the name bissextile. 2. In 1582 the error in the calendar as established by Julius Cæsar had increased to 10 days; that is, too much time had been reckoned as a year, until the civil year was 10 days behind the solar year. To correct this error, Pope Gregory decreed that 10 entire days should be stricken from the calendar, and that the day following the 3d day of October, 1582, should be the 14th. This brought the vernal equinox at March 21 - the date on which it occurred in the year 325, at the time of the Council of Nice. 3. The year as established by Julius Cæsar is sometimes called the Julian year; and the period of time in which it was in force, namely from 46 years B. C. to 1582, is called the Julian Period. 4. The year as established by Pope Gregory is called the Gregorian year, and the calendar now used is the Gregorian Calendar. 5. Most Catholic countries adopted the Gregorian Calendar soon after it was established. Great Britain, however, continued to use the Julian Calendar until 1752. At this time the civil year was 11 days behind the solar year. To correct this error, the British Government decreed that 11 days should be stricken from the calendar, and that the day following the 2d day of September, 1752, should be the 14th. 6. Time before the adoption of the Gregorian Calendar is called Old Style (0. S), and since, New Style, (N. S.) In Old Style the year commenced March 25, and in New Style it commences January 1. 7. Russia still reckons time by Old Style, or the Julian Calendar; hence their dates are now 12 days behind ours. 8. The centuries are numbered from the commencement of the Christian era; the months from the commencement of the year; the days from the commencement of the month, and the hours from the commencement of the day, (12 o'clock, midnight.) Thus, May 23, 1860, 9 o'clock A. M., is the 9th hour of the 23d day of the 5th month of the 60th year of the 19th century. MEASURE OF ANGLES. 301. Circular Measure, or Circular Motion, is used principally in surveying, navigation, astronomy, and geography, for reckoning latitude and longitude, determining locations of places and vessels, and computing difference of time. Every circle, great or small, is divisible into the same number of equal parts: as quarters, called quadrants; twelfths, called signs; 360ths, called degrees, etc. Consequently the parts of different circles, although having the same names, are of different lengths. The unit is the degree, which is part of the space about a point in any plane. The table is made up of divisors and multiples of this unit. SCALE ascending, 60, 60, 30, 12; descending, 12, 30, 60, 60. NOTES.1. Minutes of the earth's circumference are called geographic or nautical miles. 2. The denomination, signs, is confined exclusively to Astronomy. 3. A degree has no fixed linear extent. When applied to any circle it is always part of the circumference. But, strictly speaking, it is not any part of a circle. 4. 90° make a quadrant or right-angle; 60° 66 "sextant "of a circle. The terms folio, quarto, octavo, duodecimo, etc., indicate the number of leaves into which a sheet of paper is folded. A sheet folded in 2 leaves is called a folio. A sheet folded in 4 leaves a quarto, or 4to. an octavo, or 8vo. a 16mo. an 18mo. a 24mo. a 32mo. 305. COPYING. 72 words make 1 folio or sheet of common law. 90 GOVERNMENT STANDARDS OF MEASURES AND WEIGHTS. 306. In early times, almost every province and chief city had its own measures and weights; but these were neither definite nor uniform. This variety in the weights and measures of different countries has always proved a serious embarrassment to commerce; hence the many attempts that have been made in modern times to establish uniformity. The English, American, and French Governments, in establishing their standards of measures and weights, founded them upon unalterable principles or laws of nature, as will be seen by examining the several standards. UNITED STATES STANDARDS. 307. In the year 1834 the U. S. Government adopted a uniform standard of weights and measures, for the use of the custom houses, and the other branches of business connected with the General Government. Most of the States which have adopted any standards have taken those of the General Government. 308. The invariable standard unit from which the standard units of measure and weight are derived is the day. Astronomers have proved that the diurnal revolution of the earth is entirely uniform, always performing equal parts of a revolution on its axis in equal periods of duration. Having decided upon the invariable standard unit, a measure of this unit was sought that should in some manner be connected with extension as well as with this unit. A clock pendulum whose rod is of any given length, is found always to vibrate the same number of times in the same period of duration. Having now the day and the pendulum, the different standards hereafter given have been determined and adopted. STANDARD OF EXTENSION. 309. The U. S. standard unit of measures of extension, whether linear, superficial, or solid, is the yard of 3 feet, or 36 inches, |
