The true length of the solar year is 365-242217 days, or about 365 da. 5 hr. 48 m. 47 sec. The civil year is also divided into 12 calendar months, If the year exceeded 365 days by 6 hours exactly, then once in four years these hours would amount to another day. Hence, once in four years, an additional day is given to the month of February; and such years are called Bissextile or Leap years. quite 6 hours, this rule of adding one day to February every fourth year is interrupted, and the centennial years, which are not divisible by 400, are regarded as common years.* Hence, any year, (except a centennial year,) which is divisible by 4, is a Leap year, or consists of 366 days. But, since this excess is not Centennial years which are divisible by 400 are regarded as Leap years; all others are considered as common years. 1796, 1804, 1808, 1812, 1816, 1820, 1824, 1828, 1832, 1836, 1840, were all Leap years. 1800, not being divisible by 400, was a common year of 365 days; the same may be said of 1900; but the year 2000, being divisible by 400, will be a Leap year. The number of days in the respective months may be recalled by recollecting the following versification: Thirty days hath September, Which has but twenty-eight in fine, Till Leap Year gives it twenty-nine. Repeat the Table for Time. What is the length of the solar year to the nearest second? What is the more accurate value in decimals? Into how many calendar months is the civil year divided? Repeat their names and the number of days belonging to each. How often in general is an additional day added to February? What are such years styled? Is the rule of counting every fourth year Leap year correct? Are centennial years, which are not divisible by 400, Leap years? Was 1800 a Leap year? Mention the next preceding and next following Leap year to 1800. It is very desirable to be able readily to determine the number of days from any particular date to any other date. For this purpose, we will give the following *There is still a further modification which takes place at the end of every 1000 years, which it is unnecessary to explain in this place. TABLE, SHOWING THE NUMBER OF DAYS FROM ANY DAY OF ONE MONTH TO THE SAMB DAY OF ANY OTHER MONTH IN THE SAME YEAR. FROM ANY DAY OF JANUARY, MARCH, APRIL, MAY, JUNE, TO THE SAME DAY OF Jan. Feb. Mar. | Ap'l May June July Aug. Sept. Oct. Nov. Dec. 122 153 183 214 244 92 123 153 184 214 61 365 31 59 90 120 151 181 212 243 273 304 334 334 365 28 59 89 120 150 181 212 242 273 303 306 337 365 31 61 92 122 153 184 214 245 275 275 306 334 365 30 61 91 245 276 304 335 365 31 61 214 245 273 304 334 365 30 92122 153 183 JULY, 184 215 243 274 304 335 365 31 62 92 123 153 AUGUST, 153 184 212 243 273 304 334 365 31 61 92122 SEPTEMBER, 122 153 181 212 242 273 303 334 365 30 61 91 OCTOBER, 92 123 151 182 212 243 273 304 335 365 31 61 NOVEMBER, 61 92 120 151 181 212 242 273 304 334 365 30 DECEMBER, 31 62 90 121 151 182 212 243 274 304 335 365 As an example, suppose we wish the number of days from November 6th to the 15th of next April. We find November in the left-hand vertical column, and April at the top line of the table, and at the intersection we find 151 days. So that from November 6th to April 6th is 151 days; consequently, adding 9, we find 160 for the number of days between November 6th and April 15th. This table is constructed on the supposition of 28 days to February. When there are 29 days in February the proper allowance must be made. EXAMPLES. 1. How many days from May 3d to the 4th of the next July? Ans. 62 days. 2. How many days from July 4th to the 25th of the Ans. 174 days. next December? 3. How many days from March 21st to the 23d of the next September? Ans. 186 days. 4. How many days from September 23d to the 21st of the next March? Ans. 179 days. 5. How many days from June 21st to the 22d of the next December? Ans. 184 days. 6. How many days from December 22d to the 21st of the next June? Ans. 181 days. 7. How many days from March 21st to the 21st of the next June? Ans. 92 days. 8. How many days from Jan. 13th, 1848, to September 17th of the same year? Ans. 248 days. CIRCULAR MEASURE, OR MOTION. 77. By this is estimated Latitude and Longitude, and the motion of the heavenly bodies which appear to move in circles. Every circle, whether great or small, is divided into 360 degrees. The sun appears to pass completely around the earth in 24 hours, that is, it appears to move westward over 360° of longitude in 24 hours. Consequently, in one hour it will move over 4 of 360°-15° of longitude. Hence, if the difference in the longitudes of two places is 150, it will be noon at the more easterly place, just one hour before it is noon at the other place. And in all cases, the difference in time of any two places will be at the rate of one hour for every 15° of longitude between the two places. As an example, suppose the city of Washington to be 77° west of Greenwich: it is required to find what time it is at Washington, when it is noon at Greenwich. Dividing 770 by 150 we have 5 for the number of hours difference in time, that is, 5h. 8m. And as the apparent motion of the sun is westward, it must be earlier at Washington than at Greenwich. Therefore, when it is noon at Greenwich, it is 5h. 8m. before noon at Washington; that is, it is at Washington 6h. 52m. A. M. What use is made of Circular Motion? Into how many degrees are all circles supposed to be divided? Repeat the Table. Over how many degrees of longitude does the sun appear to move in 24 hours? Over how many degrees in 1 hour} What is the difference of time corresponding to 770? When it is noon at Greenwich, what time is it at Washington, 770 west of Greenwich? 78. Measures, &c., not included in the foregoing tables. |