« BROWN : 



the sun can be seen at certain times and from certain positions 

 in any point of the horizon. 



At the time of the equinoxes the sun rises in the east point 

 and sets in the west point for all the world except the veiy 

 pole. At the pole, namely, there is but one way to look, and 

 that is directly towards the equator. On that day, accord- 

 ingl}^, the sun moves in the horizon, which is the equator for 

 the polar observer. 



Confining ourselves for the sake of simplicity, now as 

 before, to the northern hemisphere, since the same reasoning 

 applies to both, it is clear that the inhabitants of the Torrid 

 Zone will, as the sun moves toward the Tropic, see him rise 

 and set more towards the north. For a line drawn in the hor- 

 izon through the sun, the observer and the centre of the earth 

 will make an angle towards the north with the plane of the 

 equator, and, consequently, with the observer's parallel. 



At the solstice the polar observer can mark no amplitude, 

 as it is defined, when the sun is rising or setting ; for the sun 

 is here, for a season, wholly free throughout the twenty-four 

 hours from the circle on which amplitude is reckoned, the 

 horizon namely. 



But if it be remembered that at the equator the horizon is 

 perpendicular to the plane of the same, and at the pole par- 

 allel to it, and that between these positions its angle with the 

 plane of the equator is constantly changing as the observer 

 moves on a meridian, it will be seen that he at the pole can 

 make the sun touch the northern horizon In^ moving south- 

 ward to the polar circle. If the expression may be permitted, 

 he tilts up his horizon to meet the sun. The sun's amplitude 

 at this moment of rising-setting is said, technically, to be east 

 or west 90° north And, proceeding with the idea, the obser- 

 ver tilts up his horizon more and more as he goes farther 

 south. Now sunrise and sunset are points common to ecliptic 

 and horizon. As the southward movement continues the two 

 circles intercept greater arcs each from the other. The extreme 



