STANDARD MEASURE OF TIME. 39 



CHAPTER IV. 



THE PERFECT REGULARITY OF THE DAILY ROTATION 

 OF THE EARTH SERVES AS THE STANDARD MEASURE 

 OF TIME, SPACE, WEIGHT, QUANTITY OF MATTER, AND 

 MECHANICAL FORCE. 



measuring time, one rotation of the earth 

 on its axis is adopted as the unit standard, 

 denoted a DAY. The minutest subdivision of 

 ti me -is 86^ P art f one rotation of the earth, 

 denoted a SECOND. 



The earth turns on its axis three hundred and 

 sixty-six times in the period of one orbital revolu- 

 tion about the sun. While the same spot on the 

 earth's equator passes under a meridian star 

 three hundred and sixty-six times yearly, it passes 

 only 365^ times under the meridian sun. Nearly 

 one entire day is lost by the circling movement of 

 the earth around the sun, as occurs when a navi- 

 gator sails from east to west around the world. 

 Consequently, each solar day is twenty-four hours 

 and four minutes long. 



A heavy body attached to the end of a rod 

 exactly 39^ inches in length, forming a pen- 

 dulum, will make precisely one swing in the 

 part of one rotation of the earth on its axis. 



All bodies used as material measures of length 



