142 Prof. Buff on Galvanic Circuits. 



measurement. These fluctuations appear only in a smaller 

 degree to be dependent on the changes of the earth's magnetism, 

 or on the changeable elasticity of the thread by which the needle 

 hangs ; in a greater measure, on the contrary, on such magnetic 

 actions as are neither to be avoided, nor entirely governed, in a 

 building not expressly erected for magnetic observations. I have 

 avoided, I think, all such disturbances, by referring all measure- 

 ments of electromotive force to the force of a constant element of 

 particular construction, which, as I have shown (Liebig's Annalen, 

 vol. lxxxv. p. 1), maintains, for months, an absolute constancy. 

 In order to show the use of this proceeding, I add some experi- 

 ments which were made on four consecutive days in the month 

 of February 1853, with the view of comparing the force of Bun- 

 sen's charcoal zinc element with those of the before-mentioned 

 constant element. 



The actions of a zinc-charcoal element on the needle are 

 marked with /3, those of the constant element, whose force 

 served as unity of measurement, with a. Each value of « and /3 

 is the mean of two deviations caused by the same current ; the 

 one east, and the other west of zero. The numbers standing in 

 the same horizontal line relate to observations which were made 

 in immediately successive times. 



1-8167 



The charcoal cylinder in these four experiments was always 

 the same, but the apparatus was put together each time afresh. 

 The force remained, as is seen, unaltered. From the direct 

 results of the deviations, small fluctuations might have been cal- 

 culated upon. These fluctuations affected, however, the two 

 constant pairs equally, and depended consequently on external 

 influences. 



In the same manner we obtained for a Daniell's pair, — 



0. *. (S. F=l2££. 



log a 



49°-0 49°-7 49°-15 49°-65 1-0201 



and for another element, when the amount of resistance in the 

 long wire was changed, — 



50°1 50°-975 50°1 1-0316. 

 The investigation of the perchloride pair (slight addition of HC1, 

 with sulphuric acid in the porcelain cell) led to these results : — 



