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OFTH6 T 



.jtVERSlTY 

 LECTUKES 



ON 



EXPERIMENTAL PHILOSOPHY, &c. 



LECTURE XXIII. 

 ASTRONOMY. 



THE VICISSITUDES OF THE SEASONS, AND 

 THE DIVISIONS OF TIME. 



THE constant inclination of the axis of the earth 

 to the plane of the ecliptic, and its parallelism, 

 produce the vicissitudes of the seasons. That 

 part of the earth which has the sun at mid-day as 

 near to its zenith as possible, consistently with its 

 latitude, enjoys the pleasant season of summer ; 

 and it is winter when the sun is as far distant as 

 possible from its zenith. As, therefore, the track 

 of the ecliptic lies between the two tropics, it is 

 evident that our midsummer must be on the day 

 of the summer solstice, or that on which the sun 

 is vertical, or in the zenith, to all that part of the 

 globe which is under the tropic of Cancer, and 

 our midwinter or winter solstice must be on that 

 day on which that part which lies under the tro- 

 pic of Capricorn has the sun vertical, or in the 



VOL II. B 



