The centimeter-gram-second system of electromagnetic units (EMU) has been used in magnetism since the latter part of the 19th century. The International System of Units (SI), a successor to Giorgi's 1901 rationalized four-dimensional meter-kilogram-second system, was adopted by the General Conference on Weights and Measures in 1960 with the ampere as the fourth base unit. However, EMU remains in common use for the expression of magnetic data. The forthcoming revision of the SI will accentuate its differences with EMU. The permeability of vacuum will no longer be a fixed constant, which recalls the Giorgi system and prompts a review of historical arguments on the concepts of magnetic flux density and magnetic field strength in vacuum. The redefinition of the ampere in terms of the fixed numerical values of two defining constants could allow for independent experimental measurements of the permeability of vacuum, i.e., determination of the magnetic constant.

中文翻译：

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电磁单位、Giorgi 系统和修订后的国际单位系统

自 19 世纪下半叶以来，厘米 - 克 - 秒系统的电磁单位 (EMU) 已被用于磁学。国际单位制 (SI) 是 Giorgi 1901 年合理化的四维米-千克-秒系统的继承者，于 1960 年被度量衡大会采用，安培作为第四个基本单位。然而，EMU 仍然普遍用于磁数据的表达。即将修订的 SI 将突出其与 EMU 的差异。真空的磁导率将不再是一个固定的常数，这让人想起 Giorgi 系统，并促使我们回顾一下关于真空中磁通密度和磁场强度概念的历史争论。