TrME-RECKONING. 103 



of the day entirely finislies. The globe must in fact make two entire 

 revolutions before any one week day runs out, consequently each and 

 every day of the week runs over 48 hours ; and, taking the whole 

 globe into account, two civil days always co-exist. The first 24 

 hours of one day co-exist" with the last 24 hours of its predecessor, 

 while the remaining 24 hours co-exist with the first 24 hours of the 

 day which follows. 



It is difficult to accept the fact that any one day lasts more than 

 24 hours ; but it can be demonstrated that it is the case. Let us 

 place together several maps of the world on Mercator's " Projection," 

 so as to represent, in consecutive order, each part of the earth's sur- 

 face as it passes the sun during several diurnal revolutions. [See 

 Plate). 



AA^, A'^A'', and A^A^, are intended to represent each a complete 

 map of the world. Within each of these limits every place on the 

 earth's surface is brought under the sun during a daily revolution. 



The vertical lines E I N R V represent meridians, for the sake of 

 simplicity selected 60*^ degrees apart, and the stars or dots at their 

 intersection denote the beginning and end of a day on each of the 

 six meridians. As the earth revolves, the sun passes successively 

 the meridians of those localities, with an interval of four hours 

 elapsing between each. 



Let us assume it to be 12 o'clock midnight on Thursday at meridian 

 A. At that moment and at that place Friday begins and runs for 

 24 hours, or on the diagram from A to A^. 



Four hours later Friday begins on meridian E, and runs four hours 

 on the second map, or into the 2nd revolution of the earth. Four 

 hours still later Friday begins on meridian / and runs eight on the 

 second map or into the 2nd revolution. This goes on from spot to 

 spot, until at last the commencement of Friday reaches the last 

 meridian, and at that point Friday runs entirely across the second 

 map to A^. Thus Friday begins at A, runs during two complete 

 revolutions of the earth, as shown on the map from A to A\ 



The diagram will thus illustrate the duration of every day in the 

 week, and it becomes obvious, when we take a general view of the 

 whole globe on any given day, say Saturday, that day begins in the 

 middle of Friday and does not end until the middle of Sunday. 

 Friday, on the other hand, beginning in the middle of Thursday, 

 runs into the middle of Saturday, while Sunday commences at the 

 moment Friday ends. To state the case differently : the same moment 



