98 



The Midnight Sun. 



It is, however, necessary, with reference to our especial 

 object of explaining the Midnight Sun, to go into further detail 

 of the unequal days and nights of different latitudes, and as some 

 little difficulty may arise from the apparent motion of the sun in 

 altitude, due to the earth's rising and sinking above his position, 

 it may be desirable first to consider the apparent paths of the 

 stars as caused by the earth's rotation on its axis, these bodies, 

 from their distance, being free from the effect produced upon 

 the sun's meridian altitude by the obliquity of the equator and 

 ecliptic, and therefore not altering their declination or distance 

 north or south from the equator. Some simple diagrams will 

 enable us to do this most effectually. In Fig. 1 the appearance 



of the heavens, as seen by an 

 inhabitant of the earth at the 

 equator, is indicated. In this 

 and the two following figures 

 the letters of reference are, 

 the same, H E, being the ob- 

 server's horizon ; N and S the 

 north and south poles of the 

 earth ; E Q, its equator ; Z 

 and Na, the zenith and nadir 

 of a place. The diagram then 

 shows that a place on the 

 equator will have the poles in 

 its horizon, and that all the 

 celestial bodies will rise and 

 set at right angles to the horizon, and will continue just as 

 long a time above it as they do below. The dotted linos re- 

 present the paths of stars or the sun, and as the rotation of 

 the earth on its axis is uniform in rate, the semicircle above 

 will be described in the same 

 time as the one below, and this 

 being twelve hours each, the 

 days and nights will bo equal 

 throughout the year. The ob- 

 server will also sco the whole 

 of tho stars in tho heavens, 

 which he can do nowhere else, H 

 although some will bo in 

 very unfavouniblo positions. 

 Passing to Fig. 2, a very 

 di Hi 'rent state of things is 

 presented to view. Here the 

 north pole is in the zenith, 

 and the ecjuator (or equinoc- 

 tial, as the circlo in tho hoavons 



