138 Electromagnetic and Calometric Absolute Measurements. 



zontal component of the earth's magnetic force (which alone 

 might make a difference of 2 units in the value of J), that he 

 has not reduced the indications of the thermometer he employed 

 to the air thermometer (a reduction which might make a dif- 

 ference of 4 units), and that he used in his experiments very 

 powerful currents and very feeble resistances (a procedure 

 which must necessarily have been attended with some slight 

 errors), no great weight will be laid upon this small difference ; 

 the previously startling discrepancy is removed. 



It can in two ways be shown that W. Weber, as we have 

 maintained, found the absolute value of Jacobi's unit of resist- 

 ance about 8 per cent, too small. 



Bosscha,in 1856*, determined according to Ohm's method the 

 electromotive force of a Daniell's element in absolute electro- 

 magnetic measure. His measurements were based on a standard 



of resistance the absolute value of which, 0*607 x 10 10 ( |, 



7 \ sec. y 



was obtained by comparison with the above-mentioned copy 

 by W. Weber of Jacobi's unit. He found the absolute elec- 

 tromotive force of a Daniell's element, in the mean out of 

 several measurements, 



= 10-258 xl oio/ ^lim*milligr.\ 

 \ sec/ / 



This result is proportional to the resistance taken as the basis 

 of the measurement ; the error committed in measuring this 

 resistance enters into the derived value of the electromotive 

 force. 



From a long series of absolute measurements of the electro- 

 motive forces of the Daniell element, the details of which shall 

 be related in another place, I have found that the lowest value 

 of the electromotive force of the Daniell element in absolute 

 electromagnetic measure is 



10-96 xl0^( , mfflim - tm 2 im g r - i \ 



\ sec. / 



that the absolute value of the electromotive force of a Daniell's 

 element of the form usually employed is 



11-30 xl QW miIlim.*milHg r .h 

 \ sec. / 



and that the highest value of the electromotive force of a Da- 

 niell's element amounts to 



11-54 xl0 i.( "»iU^mffligr.\ 

 \ sec/ / 



£. Ann. yoI. ci. p. 517. 



