TIME-RECKONING. 103 
of the day entirely finishes. 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 # J V & 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 Z, and runs four hours 
on the second map, or into the 2nd revolution of the earth. Four 
hours still later Friday begins on meridian J 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’ 
