Book II chapter 12

The Magnetick Horizon.

H orizon is the name given to the great circle, separating the things which are seen from those which are not seen; so that a half part of the heaven always is open and easily seen by us, half is always hidden. This seems so to us on account of the great distance of the star-bearing orbe: yet the difference is as great as may arise from the ratio of the semi-diameter of the earth compared with the semi-diameter of the starry¹ heaven, which difference is in fact not perceived by our senses. We maintain, however, that the magnetick horizon is a plane level throughout touching² the earth or a terrella in the place of some one region, with which plane the semi-diameter, whether of the earth or of the terrella, produced to the place of the region, makes right angles on every side. Such a plane is to be considered in the earth itself and also in the terrella, for magnetick proofs and demonstrations³. For we consider the bodies themselves only, not the general appearances of the world. Therefore not with the idea of outlook (which varies with the elevations⁴ of the lands), but taking it as a plane which makes equal angles with the perpendicular⁵, we accept in magnetick demonstrations a sensible horizon or boundary, not that which is called by Astronomers⁶ the rational horizon.

1 starry   

adj.星光照耀的, 闪亮的

参考例句：

• He looked at the starry heavens.他瞧着布满星星的天空。
• I like the starry winter sky.我喜欢这满天星斗的冬夜。

2 touching   

adj.动人的，使人感伤的

参考例句：

• It was a touching sight.这是一幅动人的景象。
• His letter was touching.他的信很感人。

3 demonstrations   

证明( demonstration的名词复数 )； 表明； 表达； 游行示威

参考例句：

• Lectures will be interspersed with practical demonstrations. 讲课中将不时插入实际示范。
• The new military government has banned strikes and demonstrations. 新的军人政府禁止罢工和示威活动。

4 elevations   

（水平或数量）提高( elevation的名词复数 )； 高地； 海拔； 提升

参考例句：

• Weight of the crust changes as elevations are eroded and materials are deposited elsewhere. 当高地受到侵蚀，物质沉积到别的地方时，地壳的重量就改变。
• All deck elevations are on the top of structural beams. 所有甲板标高线均指结构梁顶线。

5 perpendicular   

adj.垂直的，直立的；n.垂直线，垂直的位置

参考例句：

• The two lines of bones are set perpendicular to one another.这两排骨头相互垂直。
• The wall is out of the perpendicular.这墙有些倾斜。

6 astronomers   

n.天文学者，天文学家( astronomer的名词复数 )

参考例句：

• Astronomers can accurately foretell the date,time,and length of future eclipses. 天文学家能精确地预告未来日食月食的日期、时刻和时长。 来自《简明英汉词典》
• Astronomers used to ask why only Saturn has rings. 天文学家们过去一直感到奇怪，为什么只有土星有光环。 来自《简明英汉词典》