b'\x1b\x1a\x19 \x1f\x18\x1d\x17\x16Metric MattersHISTORY OF AMPERE AND KELVINBy Edmund IsakovO n Oct. 10, 1933, the eighth meeting of the General Con-ference on Weights and Measures,Ampere Kelvinalso known as CGPM, consideredUnit: ampere Unit: kelvinthe necessity of substituting inter- Symbol: A Symbol: Knational electric units with abso- Measure: electric current Measure: thermodynamic temperaturelute electric units.On Oct. 21, 1948, the ninth CGPMof negligible circular cross section,cian, physicist, chemist and philoso-meeting abolished absolute electricand placed 1 meter apart in vacuum,pher. He is best known for work in units and adopted the ampere aswould produce between these con- electromagnetism.the unit of electric current. ductors a force equal to 210 7new- In 1848, Lord Kelvin, aka William The CGPMs definition was, Theton per meter of length. Thomson, in his paper On an Ab-ampere is that constant current,The unit of electric current issolute Thermometer Scale, calcu-which, if maintained in two straightnamed after Andr-Marie Amprelated that absolute zero was equiv-parallel conductors of infinite length,(1775-1836), a French mathemati- alent to -273 C (-459.4 F) on air 12 m COATINGS! Visit us at West Hallbooth 431716WITH HiPIMS in thecemecon.com24MAY 2020 MetricMatters-2.indd 24 4/16/20 12:27 PM'