250 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 



The conference at Washington also recommended the adoption of a 

 dial of 24 hours, which has the advantage that the use of the abbre- 

 viations a. m. and p. m. is unnecessary, as is the case with a dial of 

 12 hours. Unfortunately the spread of this reform seems to have 

 nearly stopped. It is officially used at present only in Belgium, 

 Canada, Spain, France, Italy, and British India. 



The civil day commences at mean midnight. For astronomical 

 purposes a system of 24 hours is universally employed but the zero 

 hour corresponds to mean noon, so that mean astronomical time is 

 exactly 12 hours later than mean civil time. This convention was 

 adopted so that the same date could be used for all the observations 

 of a single night. Although the conference at Washington resolved 

 that as soon as practicable all astronomical and nautical dates over 

 the whole world should commence at mean midnight, astronomers 

 have not so done. English mariners indicate by p. m. the afternoon 

 hours and by a. m. those of the forenoon. 



The time corresponding to certain zones have received special 

 designations : 



Western European time, or western time, corresponding to the zone of Greenwich. 



Central European time, or central time, corresponding to the zone 1 hour east 

 of Greenwich. 



Eastern European time, or eastern time, corresponding to the zone 2 hours east of 

 Greenwich. 



Eastern standard time, corresponding to 5 hours west of Greenwich. 



Central standard time, corresponding to 6 hours west of Greenwich. 



Mountain standard time, corresponding to 7 hours west of Greenwich. 



Pacific standard time, corresponding to 8 hours west of Greenwich. 



Since 1884 many countries have adopted systems of time based 

 upon the zones and the meridian of Greenwich. In the following 

 table are given the principal nations or portions of nations, the merid- 

 ians adopted, and the differences between their standard times and 

 that of Greenwich. The plus sign ( + ) indicates that the given 

 difference must be added to Greenwich time in order to obtain the 

 time in a given country; the negative sign (— ), that it must be 

 subtracted. 



The systems of time in various countries. 



