DIVISIONS OF TIME. 



A Solar Day ia measured by the rotation of the earth 

 upon its axis, and is of different lengths, owing to the 

 ellipticity of the earth's orbit and other causes ; but a 

 mean solar day, recorded by the time-piece, is twenty-four 

 hours long. 



An Astronomical Day commences at noon, and is 

 counted from the first to the twenty-fourth hour. A Civil 

 Day commences at midnight, and is counted from the first 

 to the twelfth hour, when it is recounted again from the 

 first to the twelfth hour. A Nautical Day is counted as a 

 Civil Day, but commences, like an Astronomical Day, from 

 noon. 



A Calendar Month varies in length from 28 to 31 days. 

 A Mean Lunar Month is 29 days, 12 hours. 44 minutes, 

 2 seconds, and 5.24 thirds. 



A Year is divided into 365 days. 



A Solar Year, which is the time occupied by the Sua 

 in passing from one Vernal Equinox to another, consists*of 

 365.24244 solar days, or 365 days, 5 hours, 48 minutes, and 

 49.536 seconds. 



A Julian Year is 365 days. A Gregorian Year is 

 365.2425 days. Every fourth year is Bissextile, or Leap 

 Year, and is 368 days. The error of the Gregorian compu- 

 tation amounts onjy to one day in 3571.4286 years. 



TO ASCERTAIN THE LENGTH OF THE DAY AND NIGHT. 



At any time of the year add 12 hours to the time of the 

 sun's setting, and from the sum subtract the time of rising 

 for the length of the day. Subtract the time of setting 

 from 12 hours, and to the remainder add the time of rising 

 next morning for the length of the night. These rules are 

 equally true for apparent time. 



ooj^-jo* ' 



IMPORTANT EPOCHS A3STD EEAS. 



Destruction of Troy June, B. C. 1184. 



Building of Solomon's Temple May, B. C. 1015. 



Roman Era April 24. B. C. 753. 



Christian Era January 1, A. D, 1 ; A. M. 4004. 



Destruction of Jerusalem September 21, A. D. 69. 



Conquest of England October H, A. D. 1066. 



Declaration of American Independence. .July- 4, A. D- 1776. 



THINGS WORTH KNOWING. 



Socsd travels at tho rate of 1 142 feet per second in the 

 air, 4980 in water, 11,000 in cast-iron, 17,000 in steel, 18,000 

 in glass, and from 4638 to 17,000 in wood. 



Mercury freezes at 38 degrees below zero Fahrenheit, and 

 becomes a solid mass, malleable under the hammer. 



The greatest height at which visible clouds ever exist 

 does not exceed ten miles. 

 Air is about 816 times lighter than common -water. 

 The pressure of tho atmosphere upon every square foot 

 of tho earth amounts to 2160 lbs. Ali ordinary sized man, 

 supposing his surface to be 14 square feet, sustains the 

 enormous pressure of 30,340 lbs. 



Heat rarefies air to such an extent that it can be made 

 to occupy 5500 times the space it did before. 



The violence of tho expansion of water when freezing is 

 sufficient to cl,eave a globe of copper of such thickness as to 

 require a force of 28,000 lbs. to produce a like effect. 



During the conversion of ice into water, 140 degrees of 

 heat are absorbed. 



Water, when converted into steam, increases in bulk 

 18,000 times. 



One hundred pounds of Dead Sea water contains 46 lbs. 

 of salt. 



The mean annual depth of rain that falls at the equator 

 is 96 inches. 



Assuming the temperature of the interior of the earth to 

 increase uniformly at the rate of one degree for every 45 

 feet, at the depth of 60 miles the degree of heat would be 

 sufficient to fuse all known substances. 



The explosive force of close-confined gunpowder is six 

 and a half tons to the square inch. 



The greatest artificial cold ever produced is 91 degrees 

 below zero Fahrenheit. 



Water obstructs one-half of the perpendicular rays of 

 the sun in 17 feet, and three-fourths in 34 feet ; and less 

 than one-thousandth part reaches the depth of 200 feet ; 

 hence the bottom of deep waters is in total darkness. 



The Sun has a diameter of 885,680 miles, and its bulk is 

 1,400,000 times greater than that of the Earth. 



The Earth moves forward in its orbit. 1,640,000 miles per 

 day, 68,000 miles per hour. 1,100 miles per minute, and 

 nearly 19 miles every second. Its diameter is 7912 miles, 

 and its distance from the Sun 52,000,000 miles. The 

 Moon's diameter is 2160 miles, and its volume one forty- 

 nintli of that of the Earth. It revolves in its orbit once 

 in 204 days, at a distance of 240,000 miles from the Ear** 



