23S 
IOWA ACADEMY OF SCIENCES 
B. 
ELECTROMOTIVE FORCE OF STANDARD CELLS. 
Clark 
1872 
Clark at 15 degrees 
1.4378 
Rayleigh 
and 
Sidgwick 
1884 
Clark 
1.4345 
Kahle 
1896 
Clark 
1.4322 
Carhart 
and 
Guthe 
1899 
Clark 
1.4333 
Guthe 
1905 
Clark 
1.43296 
Guthe 
1905 
Cadium at 20 degrees 
1.01857 
Doubtless in the near future other determinations of the absolute 
value of these important electrical units will be made, some being car- 
ried on in the national physical laboratory in England, and some at the 
Bureau of Standards at the present time. It is to be hoped that in a 
couple of years steps may be taken for new international action looking 
towards a uniform legalization of electrical units throughout the civil- 
ized w'orld and of units which agree more closely with those derived 
from absolute measurements. Certainly only two can be defined as fun- 
damental, moreover, even if based upon c. g. s. units they should be con- 
crete units unaffected by the possible discovery of slight errors to be 
found in future time in the absolute values. It is true they would not 
be prototypes in the same sense as the international Kilogram and the 
meter, but there is a certain advantage in the possibility of their recon- 
structions at any time by different observers. Whether, besides the ohm 
the ampere or the volt shall be chosen as the second fundamental unit 
can hardly be predicted at the present time; that depends upon the ques- 
tion which of the two wull prove to be reproducible with the highci 
degree of accuracy. Under otherwise equal conditions preference shoula 
be given to the coulometer since the current is found in terms of the 
fundamental units alone, while in the present determinations of the volt, 
the ohm enters always as a factor and with it the error made in its 
measurement, or in other words, the present methods for the determina- 
tion of the volt arc not strictly absolute methods. Whatever decision 
may be reached it is certain that there will be a closer agreement than 
under the present law between scientific results and the system used in 
the commercial world. 
