44 1HE YEAR. 



lower and lower to the south at mid-day, is vertical at 

 a point in latitude 23 28' south. Of course it is then 

 noon of the longest day at that point ; but, because of 

 the fraction already mentioned, it does not happen 

 twice in succession at the same point, but is nearly six 

 hours in time, or 90 in longitude further to the west 

 every year than in the year immediately preceding. 

 From this point the apparent motion of the sun is west- 

 ward, tending a very little to the north, so that, though 

 it be again mid-day at the place where the observation 

 commenced, in twenty-four hours, the sun is not over 

 head, but to the north, only the difference in one day 

 is so small that it cannot be observed without very fine 

 instruments. 



Every succeeding diurnal rotation of the earth upon 

 its axis will procure another apparent revolution round 

 the earth of the point where the sun is vertical, only 

 each time that the sun comes to the first meridian 

 that in which the tropic or turning point is situated he 

 will be farther and farther to the north of that point, 

 and as the revolutions become more numerous, the 

 daily northing will become greater. After about ninety 

 revolutions, the sun will be over head at some point of 

 the equator; it will be the vernal equinox in the 

 northern hemisphere; a quarter of the year will have 

 elapsed; and it will be at some time on the 21st of 

 March, reckoning the time as in England. Some 

 notion of the difference of rate at which the northing 

 changes through this quarter, may be formed, when it 

 is mentioned that the seventy miles nearest the tropic 

 requires about sixteen revolutions, or days, while the 

 seventy miles nearest the equinox requires only four ; 



