ROTATION OF THE EAETH. 11 



shore appear to pass along in an opposite direction to that 

 in which the ship is going. It is the same with the earth ; 

 the sun, which appears to move, is stationary, while the 

 earth is going round it ; and the result is, while the earth 

 turns round on its axis the whole firmament appears to 

 move, we lose sight of those stars which are to the west- 

 ward, which are then said to " set," while those to the east- 

 ward, constantly coming into sight, are said to " rise," the 

 whole appearing to pass from east to west, while in reality 

 the earth's surface is passing from west to east. At the 

 equator, or that part of the earth which lies midway between 

 the poles, the sun and stars appear to rise and set perpen* 

 dicularly to the horizon and at equal times above and below 

 it, it is therefore 12 hours day and 12 hours night ; in places 

 not situated on the equator, they do not rise and set perpen- 

 dicularly to the horizon, but form portions of circles at 

 greater or less altitudes in the heavens, and the nearer the 

 observer is to either of the poles, the smaller the circle, and 

 the more of it is seen ; so that, at the poles, any star situated 

 exactly overhead does not appear to move at all. This place 

 is called the north pole of the heavens, and the nearest star 

 to it is called the " polestar," which neither rises nor sets, 

 and, as it always keeps the same position, serves as a guide 

 to mariners. All this is the effect of the diurnal motion of 

 the earth, its annual motion not affecting the position of 

 the stars, they being at such an immense distance that the 

 circle which the earth forms in passing round the sun 

 although nearly 200,000,000 miles across is as a mere 

 point in proportion. But not so with the sun : as before 

 stated, at the equator it is twelve hours above the horizon 

 and the same time below it ; now, as we approach towards 

 the poles, it forms at each rotation an arc above the horizon, 

 lower and lower, until at the poles its daily rising and 

 setting is lost altogether, and there would never be daylight 

 there, provided that the earth was only subject to the diurnal 

 motion (fig. 9) ; but as the earth turns upon an oblique axis, 

 the north and south poles share the blessing of daylight 

 between them, so that through one-half of the earth's orbit 

 the north pole is towards the sun, as shown in the figure, and 



