Math & Physics Problems Wikia
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方家以磁石磨针锋,则能指南,然常微偏东,不全南也。水浮多荡摇,指爪及碗唇上皆可为之,运转尤速,但坚滑易坠,不若缕悬为最善。其法取新纩(kuàng)中独茧(jiǎn)缕,以芥子许蜡缀于针腰,无风处悬之,则针常指南。其中有磨而指北者。予家指南、 北者皆有之。磁石之指南犹柏之指西,莫可原其理。


Mengxi Bitan Chapter 24 Zazhi (Part I) 18

Diviners can make a needle point to the south by rubbing it with magnetite. However the needle often inclines to the southeast direction, not pointing to due south. If the needle is floating on water, it often sways. The needle may be placed on a nail or the edge of a bowl, which may make it rotate a bit more flexibly, but the hard and smooth surface may make it easily fall off. The best way is to hang the needle with a silk thread. If we take a newly-reeled raw silk and paste it to the middle of the needle with wax similar to a seed of leaf mustard, and hang up the needle in a windless place, the needle will often point to the south. Some needles may point to the north after being rubbed with magnetite, for instance, in my house some needles point to the south while others point to the north. When the needle rubbed with magnetite points to the south, just as the cypress tree leans to the west. Nobody knows the reason why it is so.


看风水的人用磁石去磨针尖,针尖就能指出南方,不过常常略为偏东,并不完全指向正南。把 磁针浮在水面上,常晃荡不停。也可以把磁针放在指甲上和碗口上,磁针转动更灵快些,但这上面又 硬又滑,磁针容易掉落,不如用丝线悬挂为最好。其方法是从新丝棉中抽取一根蚕丝,用芥菜籽大小的一点蜡粘连在磁针的腰部,悬挂在没有风的地方,磁针就常常指向南方。磁针也有经磨后指向北的。我家的磁针,指南指北的都有。磁石的指南,如同柏树的指西,不能推究出其中的道理。