我国古代对磁场的认识及其应用有哪些?以及给世界的航海带来了什么好处?

2025-02-27 02:30:00
推荐回答(1个)
回答(1):

1. 磁石的吸铁性及其应用
  我国是对磁现象认识最早的国家之一,公元前4世纪左右成书的《管子》中就有“上有慈石者,其下有铜金”的记载,这是关于磁的最早记载。类似的记载,在其后的《吕氏春秋》中也可以找到:“慈石召铁,或引之也”。东汉高诱在《吕氏春秋注》中谈到:“石,铁之母也。以有慈石,故能引其子。石之不慈者,亦不能引也”。在东汉以前的古籍中,一直将磁写作慈。相映成趣的是磁石在许多国家的语言中都含有慈爱之意。
  我国古代典籍中也记载了一些磁石吸铁和同性相斥的应用事例。例如《史记·封禅书》说汉武帝命方士栾大用磁石做成的棋子“自相触击”;而《椎南万毕术》(西汉刘安)还有“取鸡血与针磨捣之,以和磁石,用涂棋头,曝干之,置局上则相拒不休”的详细记载。南北朝(512~518年)的《水经注》(郦道元)和另一本《三辅黄图》都有秦始皇用磁石建造阿房宫北阙门,“有隐甲怀刃人门”者就会被查出的记载晋书·马隆传》的故事可供参考:相传3世纪时智勇双全的马隆在一次战役中,命士兵将大批磁石堆垒在一条狭窄的小路上。身穿铁甲的敌军个个都被磁石吸住,而马隆的兵将身穿犀甲,行动如常。敌军以为马隆的兵是神兵,故而大败(“夹道累磁石,贼负铁镗,行不得前,隆卒悉被犀甲,无所溜碍”)。
  古代,还常常将磁石用于医疗。《史记》中有用“五石散”内服治病的记载,磁石就是五石之一。晋代有用磁石吸出体内铁针的病案。到了宋代,有人把磁石放在耳内,口含铁块,因而治愈耳聋。
  磁石只能吸铁,而不能吸金、银、铜等其他金属,也早为我国古人所知。《淮南子》中有“慈石能吸铁,及其于铜则不通矣”,“慈石之能连铁也,而求其引瓦,则难矣”。
2. 磁石的指向性及其应用
  在我国很早就发现了磁石的指向性,并制出了指向仪器 司南。《鬼谷子》中有“郑子取玉,必载司南,为其不惑也”的记载。稍后的《韩非子》中有“故先王立司南,以端朝夕”的记载。东汉王充在《论衡》中记有“司南之杓(勺子),
投之于地(中央光滑的地盘),其柢(勺的长柄)指南”。
  不言而喻,司南的指向性较差。北宋时曾公亮与丁度(990~1053)编撰的《武经总要》(1044年)在前集卷十五记载了指南鱼的使用及其制作方法:“若遇天景噎(阴暗)霾,夜色瞑黑,又不能辨方向……出指南车或指南鱼,以辨所向……鱼法,用薄铁叶剪裁,长二寸阔五分,首尾锐如鱼形,置炭中烧之,候通赤,以铁钤钤鱼首出火,以尾正对子位,蘸水盆中,没尾数分则止,以密器收之。用时置水碗于无风处,平放鱼在水面令浮,其首常南向午也”。需要特别指出的是,这里极为清晰地论述了热退磁现象的应用。当烧至通赤时,温度超过居里点,磁畴瓦解,这时成为顺磁体。再用水冷却,磁畴又重新恢复。这时鱼尾正对子位(北方),在地磁场作用下,磁畴排列具有方向性,因而被磁化。还应注意到,“钤鱼首出火”时“没尾数分”,鱼呈倾斜状,此举使鱼体更接近地磁场方向,磁化效果会更好。从司南到指南鱼,无疑是一个重大进步,但在使用上仍多有不便。
我国古籍中,关于指南针的最早记载,始见于沈括的《梦溪笔谈》。该书介绍了指南针的四种用法:水法,用指南针穿过灯芯草而浮于水面;指法,将指南针搁在指甲上;碗法,将指南针放在碗沿;丝悬法,将独股蚕丝用蜡粘于针腰处,在无风处悬挂。磁针的制作,采用了人工磁化方法。正是由于指南针的出现,沈括最先发现了磁偏现象,“常微偏东,不全南也”。
  南宋时,陈元靓在《事林广记》中记述了将指南龟支在钉尖上。由水浮改为支撑,对于指南仪器这是在结构上的一次较大改进,为将指南针用于航海提供了方便条件。
  指南针用于航海的记录,最早见于宋代朱彧(yù)的《萍洲可谈》:“舟师识地理,夜则观星,昼则观日,阴晦观指南针”。以后,关于指南针的记载极丰。到了明代,遂有郑和下西洋,远洋航行到非洲东海岸之壮举。

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