538 PROFESSOR W. E. AYRTON, MR. T. MATHER AND MR. F. E. SMITH : 



and using this ratio we get 



CxR for Clark cell at 15G = T432 3 ; 



GUTHE'S value of CxR for Clark cell at 15C. = 1-43296. 



The difference is in the same direction as that between the cadmium cells, but greater 

 in proportion. 



SECTION 13. CONCLUSIONS. 



From the measurements and observations detailed in the previous pages we may 

 conclude that the current weigher, constructed on the lines described, is a most 

 excellent instrument, capable of yielding results of very high precision, and worthy of 

 acceptance as an international standard instrument for the absolute determination of 

 the ampere. We therefore hope that other countries will make balances on similar 

 lines, in order to realise one of the fundamental electrical units in an exact manner. 



So far as we are aware, the accuracy attainable by the new balance far exceeds 

 that secured in any previous absolute determination of any electrical unit, and we 

 may infer that of all the electrical units the ampere is now the one best known. 



Further, we may infer that cadmium cells can be set up so as to be remarkably 

 constant in E.M.F. The observations made on cell No. 2, set up by one of us 

 (F. E. S.), extended over a period of 19 months, and during the whole of that period 

 its measured E.M.F. seldom differed from the mean by more than 1 part in 100,000. 



Of the 71 determinations of E.M.F. made 



7 are within 1 in 1,000,000 of the mean, 

 14 2 1,000,000 



28 5 1,000,000 



53 10 1,000,000 



66 15 1,000,000 



70 20 1,000,000 



Only one determination out of the whole 71, and this one of the earliest, differs 

 from the mean by so much as 1 part in 59,000. 



It is of interest to mention that of the 71 determinations just referred to 26 were 

 made by the same pair of observers (T. M. and F. E. S.), and these show a still closer 

 agreement, viz., of 26 determinations 



6 are within 1 in 1,000,000 of the mean, 



8 2 1,000,000 

 11 5 1,000,000 

 19 10 1,000,000 

 25 15 1,000,000 



Only the early one previously mentioned differed from the mean by more than 



