THE YEAR. 



should have exactly the same length. The same condition is 

 indispensable ; and for the same, and even stronger, reasons in 

 the case of the annual unit. Yet the natural standard from 

 which that unit is taken, the periodical return of the seasons, like 

 the periodical return of the sun to the meridian, is subject to a 

 certain variation. It is on that account unsuitable for a standard 

 measure of time. This defect, however, is removed by an expe- 

 dient similar to that by which the mean solar day was substituted 

 for the apparent solar day. A fictitious period is assigned to the 

 return of the seasons, which is a mean between the extreme 

 variations of the actual period which marks their successive 

 returns, and this fictitious period, which is invariable and never 

 differs much from the real period, being sometimes a little more 

 and sometimes a little less, is adopted as the chronological year. 



Unfortunately for the facility of chronology, however, neither 

 this nor any other standard measure of time based upon the 

 succession of seasons, consists of an exact round number of days 

 without a fraction ; nor has the fractional part remaining over a 

 whole number of days the advantage of amounting by any extent 

 of repetition to a day, or even to any whole number of days. 



This circumstance, "as will presently appear, has been productive 

 of grave inconvenience in history and chronology. 



74. In their first rough attempt at the establishment of the 

 annual standard of time, the Egyptians gave the year 360 days, 

 divided into twelve equal months of 30 days. 



This is supposed to have been the origin of the division of the 

 circle into 360 degrees, and indeed of the prevalence of a duode- 

 cimal modulus in many other popular measures. 



The subsequent addition of the five complementary days is 

 attributed to an Egyptian god or hero called by the Greeks 

 HEKMES, with the distinguishing appellation of TEISMEGISTOS, 

 thrice-greatest. 



75. This interval of 365 days was as near an approximation to 

 the period of the seasons as could be made in round numbers. 

 Nevertheless its continuance would, after the lapse of a certain 

 time, have been the cause of inextricable confusion. Let us see 

 whether we cannot make this apparent. 



The true period marked by the return of the seasons is now known 

 to differ from 365| days by a little more than eleven minutes. This 

 difference, minute as it is, has been the cause of great difficulties 

 in history and chronology. Let us, however, for the present put 

 it out of view, and take the year as being 365| days exactly. 



After the lapse of one year of 365 days the seasons would, 

 therefore, return a quarter of a day later than in the preceding 

 year. After another year of 365, they would return half a day 



155 



