天然磁石勺“司南”实证研究

Empirical Research on the Loadstone Spoon “Si Nan” in Ancient China

1945年王振铎提出司南复原方案,并制作"磁石勺"司南,其他研究者一直未能重复实现此方案,导致对唐以前是否可能发明磁性指向器存在长期争议。磁石是古人对具有显著天然剩余磁性的矿石的统称,其磁性较强者有磁铁矿、磁赤铁矿与磁黄铁矿等。采集到与古文献记载磁性相近的磁石,制成了具有良好指极性的磁石勺。通过新研制的"磁矩测量装置",发现按古代工艺切割、摩擦等造成的退磁非常轻微;加工后形状变化导致磁化强度略有降低,数十天后恢复稳定。古地磁学研究表明,两千多年来以洛阳、天水、北京为代表的中原、关中和华北地区地磁水平方向分量呈显著M形变化,先秦至唐中期正处于高峰期,此期间磁石勺指向性显著提升。实验显示磁石水浮法、悬吊法及"铜勺盛放磁石"等有一定可行性,但缺点明显;"铁勺盛放磁石"、"钢勺磁化"可行性差。古文献中"司南"、"针"词频变化与地磁场水平分量的演变高度对应。磁石指向器的制作方法决定其不易辨别地磁偏角,不能以未发现地磁偏角否定天然磁石指向器的发明。唐以前发明磁石指向器的可能性是存在的,磁石勺是最佳方案。

A reconstruction of the ＂south pointing loadstone spoon＂ was presented by Wang Zhengduo in 1945,though subsequent researchers have not been able to reproduce this design.As a result,there has been a longstanding controversy among academics as to whether it was possible that a magnetic pointing device had been invented prior to the Tang dynasty or not.In ancient China,＂ci shi＂ 磁石 is the collective name for high natural-remnant iron ore exhibiting strong magnetism,such as magnetite,maghemite and pyrrhotite.some loadstones that mainly contained high natural-remnant magnetism have been found in Chicheng,Hebei Province.The magnetism of these loadstone specimen are very similar to the loadstones recorded in ancient Chinese literature.Thus,some loadstone spoon were successfully constructed and can point south very well.In addition,a new ＂magnetic moment measuring device＂ was successfully developed.It was shown that,if we use traditional cutting and polishing methods,the demagnetization of the lodestone is very slight; shape change after processing may lead to a measurable magnetization intensity reduction,but it turns stable again after a few weeks.According to paleomagnetism research,over 2000 years,the horizontal component of the geomagnetic field in the Central Plains,Guanzhong Plain and North China,with Luoyang,Tianshui and Beijing as their centers,has undergone an M-shaped change.From the pre-Qin period to the mid Tang dynasty,the horizontal component of the geomagnetic field reached an all-time high,with the result that the south pointing effectiveness of the spoon-shaped loadstone increased sharply.Experi-ments show that while other restorations,such as the ＂water floating method＂,＂hanging method＂ and ＂copper spoon loadstone＂,can also point southward effectively,defects remain obvious in comparison with the ＂spoon-shaped loadstone＂.In addition,the ＂magnetized steel spoon＂ and ＂steel spoon loadstone＂ do not work very well.Furthermore,changes in the frequency of the use of the words ＂south pointing（si nan）＂ and ＂needle （zhen）＂ in historical documents corresponds closely with the evolution of the horizontal component of the geomagnetic field.The production method of the loadstone magnetic pointing device has already determined its weakness in the detection of magnetic declination.Therefore,the fact that the geomagnetic declination was not found cannot lead to a denial of the invention of such a magnetic pointing device.In summary,it is possible that the magnetic pointing device was invented before the Tang dynasty,and that the spoon-shaped loadstone can be considered an optimum design.