ABSOLUTE ELECTRIC MEASUREMENT. 4 1 



and in the next paper describes another step in electrical 

 measurement, which, besides being of primary importance in 

 leading him on to his final goal, constitutes him the 

 father of the present system of absolute units in science. 

 This was the adoption of a definite quantitative unit of 

 electricity. The connection between this step and his last 

 experiments may be clearly inferred. In these he wanted 

 to obtain a measure or estimate of the quantity of zinc 

 consumed in supplying the current he was using. The 

 actual consumption in the battery included besides this, that 

 which was wasted by local action through the imperfections 

 of the batteries. To eliminate this wasted zinc, he made 

 use of " Faraday's discovery of the definite quantity of 

 electricity associated with the chemical equivalents of the 

 bodies ; " the current caused by the consumption of each 

 equivalent of zinc in the battery being capable of dissociating 

 one equivalent of the hydrogen in the voltameter. To 

 avail himself of this law, his galvanometer " was connected 

 with an apparatus furnished with fine platinum electrodes. 

 A current was transmitted through the instrument, and 

 after a few minutes the current was broken, and the hydrogen 

 measured in a graduated tube." The mean of ten trials 

 showed that "076 gr. of water was decomposed per hour 

 by the current indicated by each unit of my former 

 numbers." The decomposition of 9 grains of water, i.e. t one 

 grain of hydrogen, would represent the solution of one equiva- 

 lent (32*3) of zinc, so that the current represented by each 

 ■degree of his galvanometer represented the solution of 27*27 

 grains of zinc. He had made these experiments and calcula- 

 tions before March 10th, 1840, as they are included in the 

 tables in his 7th letter, but the determination of adopting them 

 as a general quantitative unit of electricity seems to have been 



