INTRODUCTION. IX. 



July 23 ; Virgo the Virgin nj?, August 23 ; 

 Libra the Balance zD=, September 23 ; Scorpio 

 the Scorpion wt, October 23 ; Sagiflarins the 

 Archer ^, November 22 ; Capricornus the Wild 

 Goat ]CP, December 23 ; Jqnarius the Water- 

 b&arpr ,;»', January 19 ; and Pisces the Fishes Ky 

 feoruary 18. 



^ The Seasons may be thus explained. The 

 poles of the earth being inclined to the plane of the 

 orbit, it happens that there is a perpetual variation 

 of the relative length of day and night ; there will 

 therefore be two points in the orbit, or in other 

 words two days in the year, in which day and 

 night are of equal length, and these are call d the 

 Equinoxes ; the first or vernal equinox is when 

 the sun enters T, the second or autumnal is when 

 he enters =0= . There will also be one day in the 

 year when the day is longest and the night 

 shortest, and this is whe)i the sun enters as ; the 

 heat is then the greatest, and as the change in the 

 variation of daylight is less about this time than 

 about the equinoxes, it is called the summer 

 solstice. Conversely, in tlie opposite point in the 

 heavens, is the winter solstice. The fom* sea- 

 sons of the year. Spring, Summer, Autumn, and 

 Winter, are four artificial divisions of the year, 

 which correspond to the above periods. Each 

 season, if we regard the relative length of the 

 days therein, ought to begin and end at periods 



