间的距离，就形成了十字架二和水平线之间的角距。为了把所得的这个角度固定下来，他用刺针把一根木条横钉在圆规的两只脚上，这样就可以把它们之间的角度适当地保留下来。
做完了这一步工作，下一步只要计算一下角度就行了。但是首先要把水平线的俯角考虑在内，因此必须再到海平面上去进行观察，量一下峭壁的高度。有了上述的角度就可以求出十字架二的高度，从这里也可以求出天极在水平线上的高度，也就是海岛的纬度，困为地球上任何一个地方的纬度都永远等于当地天极在水平线上的高度。
to the south the horizon， lighted by the first rays of the moon， was very clearly defined against the sky.
at this moment the southern cross presented itself to the observer in an inverted position， the star alpha marking its base， which is nearer to the southern pole.
this constellation is not situated as near to the antarctic pole as the polar star is to the arctic pole. the star alpha is about twent
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