555 



The specific resistances of the specimens of copper wire from the 

 manufactories A, B, C, D, of which a comparative statement is given 

 in the first Table above, I have estimated in absolute measure by 

 comparing each with F 2 , of which the resistance in absolute measure 

 is 6,580,000 x -1999, or 1,316,000. The various results reduced to 

 specific resistances per grain of mass per foot of length are collected 

 in the following Table, and shown in order of quality in connexion 

 with four determinations of specific conductivity by Weber . 

 Specific Conductivities of specimens of Copper expressed in British 

 Absolute Measure. 



Description of Metal. 



Specific resistances. 



Copper wire A No. 22 7,600,000 



Wire of electrolytically precipitated copper : 



Weber(l) 7,924,000 



Copper wire B No. 22 7,940,000 



Ordinary No. 18 copper wire 8,100,000 



Copper wire C No. 22 8,400,000 



Weber's copper wire : Weber (2) 8,778,000 



No. 14 strand specimen, once covered 8,960,000 



Kirchhoff s copper wire : Weber (3) 9,225,000 



No. 14 strand specimen, thrice covered 10,400,000 



Jacobi's copper wire : Weber (4) 10,870,000 



No. 16 wire specimen, thrice covered 11,700,000 



Ditto, twice covered 1 1,970,000 



Ditto, not covered 1 1,850,000 



Ditto, once covered 12,410,000 



No. 14 strand specimen, twice covered 12,590,000 



Slip of fine sheet-copper 13,600,000 



Copper wire D No. 22 13,800,000 



No. 14 strand specimen, not covered 14,750,000 



Slip of common sheet-copper 22,300,000 



). The numbers in the last column, headed " Specific resistances re- 

 seconds.-' 



duced to British measure," express the resistances of conductors composed of ten 

 different qualities of metal, and each one foot long and weighing one grain. It 

 is impossible to over-estimate the great practical value of this system of absolute 

 measurement carried out by Weber into every department of electrical science, 

 after its first introduction into the observations of terrestrial magnetism by Gauss. 

 See"Messungengalvanischen Leitungswiderstande nach einem absoluten Maasse," 

 Poggendorff's Anualen, March 1851. See also the author's articles entitled " On 

 the Mechanical Theory of Electrolysis," and " Application of the Principle of 

 Mechanical Effect to the Measurement of Electromotive Force, and of Galvanic 

 Resistances in Absolute Units," Philosophical Magazine, December 1851. 

 VOL. VIII. 2s 



