The Midnight Sun. 103 



Let us sum up the teaching of these diagrams. To all 

 places at the equator the days and nights are always of equal 

 length. To all other places, except the poles, the days and 

 nights are never equal, except at the equinoxes. To all parts of 

 the world the days and nights are equal at the vernal and 

 autumnal equinoxes, about the 21st of March and 23rd of 

 September, when the sun enters the signs Aries and Libra, 

 and has no declination. 



To all places having the same latitude, the days and nights 

 are always of equal length at the same particular time of year. 



To all places north of the equator, the longest day and the 

 shortest night are when the sun has his greatest north decli- 

 nation, and is on the Tropic of Cancer ; and their shortest day 

 and longest night when the sun has his greatest south declina- 

 tion, or is on the Tropic of Capricorn. In southern latitudes 

 the reverse is the case. 



To all places at the Arctic and Antarctic circles, when the 

 sun has his greatest declination, he appears without setting for 

 twenty-four hours, the length of their longest day, although the 

 continuous daylight may last for weeks, as the sun sinks so 

 little below the horizon that the twilight is sufficient for all 

 purposes throughout the night. To all places within those circles 

 the length of the longest days and nights increases the nearer 

 the places are to the poles. 



At the north pole, from the 20th of March to the 23rd of 

 September, the sun is constantly above the horizon, and below 

 it through the opposite interval. There is, therefore, during 

 the whole year, but one day and one night, each of six months 

 duration ; but no one has yet reached the pole to experience 

 this effect. In speaking of the long and dreary winter night, 

 lasting for many months, which these illustrations show to be 

 the lot of polar regions, we should not lose sight of the com- 

 pensating influences. Thus, although the sun may be for months 

 below the horizon, still he is rarely as much as 18 degs. lower 

 than that circle, and therefore, owing to the existence of an 

 atmosphere and its property of refraction, the amount of twi- 

 light is very considerable; and if we remember how strong 

 this is during our summer, when for one month before and 

 one after the longest day, we are said to have " no real night," 

 the importance of this beneficial arrangement becomes mani- 

 fest.* Again, the full moon is always opposite to the sun, and 



* As far as 84^ degs. north latitude, the sun approaches within 18 degs. of 

 the horizon at mid-winter, and therefore relieves the long night of three or four 

 months, every twenty-four hours, with a short twilight. Even at the North Polo 

 the sun is not more than 18 degs. below the horizon, till November 12th, and 

 comes within that distance again on January 29th ; the 78 days between being 

 the only period of total night. From September 21st, to November 12th, and 

 from January 29th to March 21st, although the sun is absent, there is twilight. 



