ANNUAL SOLAR ACTIOX. 53 



pass within the parallel of 66 32' north (the Arctic 

 polar circle). The days, or daily portions of sun, between 

 those parallels, are of all varieties of length, from 24 

 hours to ; gradually less and less from south to north, 

 more than 12 hours south of the equator, just 12 

 there, and less than 12 in every place farther to 

 the north. There is remarkably little change in the 

 daily influence of the sun at this season, though the 

 heat produced by its continued presence augments ra- 

 pidly in the south, and the cold that results from its 

 absence, in the north. At all seasons the daily change 

 is greater, the farther that the place is from the equator ; 

 but still, the change in the length of the day is so little, 

 that for twelve days before and twelve after the solstice, 

 the whole alteration is only eight minutes in the latitude 

 of London, while during an equal period before and after 

 the equinox, it is more than an hour and a half. This 

 continued uniformity in the length of the day is the 

 cause of the remarkably steady weather which takes 

 place at, or rather a little after, the midsummer and mid- 

 winter in high latitudes ; and it is also the cause why 

 the winter is so much more unpleasant in lower latitudes 

 where the temperature keeps vacillating near the freez- 

 ing point. 



As the year advances, and the daily change in declina- 

 tion becomes more rapid, the daily changes of tempera- 

 ture are greater ; and the weather in the low latitudes is 

 irregular and broken. In very high latitudes, the 

 change, especially that from winter, is not so felt, because 

 the coating of snow with which the earth is covered, 

 reflects off part of the heat of the sun, and consumes 

 part by evaporation. When the equinox is past, the 



