employed for determining the Ohm. 275 



be 0*9830; according to F. Kohlrausch it is 0*9717; accord- 

 ing to F. Weber 0*9550; and according to Lord Bayleighand 



Mrs. Sidgwick 0-9413 / 10 9 centim - ) T h e first ohm con . 



V sec. /• 



structed by the British Association, according to F. Kohl- 

 rausch is 1*0196; according to Kowland 0*9910, and according 



to Kayleigh and Schuster 0*9893 of the true ohm (l0° cenihn \ 



Hence at any rate it is indicated that the final determina- 

 tion of the ohm must not rest alone on experiments made only 

 according to one method and carried out at one place. Fur- 

 ther, the results of each separate method (as I have already 

 mentioned) offer security against possible constant errors only 

 if they are obtained from entirely independent series of ex- 

 periments, made -with apparatus varied in all possible ways. 

 Since investigations are already in progress in different places, 

 with excellent apparatus and according to different methods, 

 ve may shortly expect to be in a position to compare together 

 the data which they yield, and so to attain as reliable a final 

 result as possible. 



In such important and permanent determinations as those of 

 the electrical units, a delay of a few months is of no import- 

 ance whatever in comparison with the reliability of the result to 

 be obtained. Any introduction of the ohm as given by detached 

 series of observations and distribution of copies for practical 

 use would therefore be premature and without authority. 



The Commission appointed for the determination of the 

 electrical units does not complete its task by simply deter- 

 mining the ohm. It is further necessary to construct at 

 least one of the two remaining units, e. g. the volt. Since it 

 is at present impossible to construct this in a form capable of 

 reproduction, it will be necessary first to compare electro- 

 motive forces with those of a constant element whose electro- 

 motive force is known in volts. We are therefore in the same 

 case as if, wishing to measure a length in metres, we were 

 obliged to employ a yard measure whose ratio to the metre 

 was known. So much the more thoroughly are we obliged 

 to investigate the electromotive forces of the galvanic cells to 

 be employed as intermediate measures, and their dependence 

 upon external conditions. The cell invented by Latimer 

 Clark has indeed been shown to be capable of reconstruction 

 of exactly the same electromotive force ; at the same time it 

 can only be employed for electrostatic measurements, since it 

 becomes polarized Avhen used to produce a current. Obser- 

 T2 



