ANNO DOMINI. 



constantly raised in society as to whether such or such a day or 

 month belonged to the eighteenth century or to the nineteenth. 



The first day and the starting point or zero of the Christian 

 chronological scale was the midnight with which the 1st January, 

 1 A.D. commenced. This was the moment, therefore, at which 

 the first century began, and it ended evidently when, dating from 

 that moment, 100 complete years had elapsed. The first century, 

 therefore, terminated and the second began at the midnight 

 between the 31st December, 100 A.D. and the 1st January, 101 

 A.D. In like manner the second century terminated and the 

 third began at the midnight between the 31st December, 200 A.D., 

 and the 1st January, 201 A.D. It is evident, therefore, that the 

 entire year 100 A.D. belonged to the first century, and the entire 

 year 200 A.D. to the second century ; and, in the same manner, 

 it follows that the entire year 1800 A.D. belonged to the eighteenth 

 century. The eighteenth century therefore commmenced with 

 the 1st January, 1701 A.D., and terminated with the 31st Decem- 

 ber, 1800 A.D., both these days belonging to that century. In 

 like manner the first day of the nineteenth century was 1st Jan., 

 1801 A.D., and its last day will be 31st December, 1900 A.D. 



10. One of the series of dates predicted in the almanack are 

 those which mark the commencement of the seasons. The winter 

 terminates and the spring commences at the moment of the vernal 

 equinox; the spring terminates and the summer commences at 

 the moment of the summer solstice ; the summer terminates and the 

 autumn commences at the moment of the autumnal equinox, and 

 the autumn terminates and the winter commences at the moment 

 of the winter solstice. The conditions which determine the 

 equinoxes and solstices have been explained in our Tract on 

 " Time." 



Owing to a certain small variation in the rate at which the sun 

 moves annually round the firmament the cause of which has 

 been explained in the same Tract the seasons are not equal in 

 length. The following are their lengths respectively : 



D. H. M. 



Spring 92 20 50 



Summer 93 14 7 



Autumn 89 17 49 



Winter 89 1 2 



365 5 48 



If the civil year, that is the year of the almanack, were iden- 

 tical with the equinoctial year, the seasons would commence 

 respectively always upon the same days of the year. But 

 although the civil year in the long run does not vary to any 



