AJteruatiug Currents to Ccdibration of Capacitij-ho.ves. 11?) 



and Ro i^i't^ those required for charging the condensers ; the 

 heating-eti'ects of these currents are comparatively small, 

 especially as the key, K, supplying the bridge is only 

 momentarily depressed. The condition for a balance in 

 De Sautv's method is that CiRi^i^^R^- Now the tanofents 



of the anole of the lag in the two limbs of 



lie bridge are 



( liip — -r~ )/ i^i ''^iiJ ( L'P— f^ — )/H2? ^^^^ since Li and Lg are 

 \ ^npyj \ ^2M / 1 \ 



both approximately zero, the lags become tan"~M — t^-h — ) 



and tan~M — p ,, — I, so that when the condition (^^i = {)2^2 



is satisfied the lags are precisely the same. 



We had in our possession a capacity-box, Elliott No. 65, 

 consisting of five capacities labelled "5, '2 A, "2 B, '05 A., and 

 •05 B. These capacities could be divided at any junction 

 into two groups, the two groups being in series and the 

 members of each group being joined in parallel ; they were 

 also capable of being used singly or together. We took the 

 capacity labelled "5 as having a true capacity of 0*5 M.F., and 

 compared each . of the other capacities and various com- 

 binations of them with it, and obtained the results given in 

 the following table. 



Table I. 



Results obtained using 



Coil B. 



Ci=:0-5 



M.F. 



Capacity tested. 



U,. 



E,. 



^-^^•1, 



Calculated 

 values of C.,. 









M.F.'s. " 





•05 B 



1970-3* 



19738 



•049912 



Assumed 



•05 A 



1970-3 



19722 



•049952 





•2B 



985-2 



2483-6 



•19834 





•2 A 



985-2 



2-192-7 



•19762 





•05 B 4- 05 A 



1970-3 



98fi9-6 



•09982 



•09986 



•2B + -05B 



985 2 



1984-1 



•24827 



•24825 



•2B4-05A 



985-2 



1983-9 



•24830 



•24829 



•2A-f-05B 



985 2 



1989-6 



•24750 



•24753 



i -2 AH- 05 A 



985-2 



1989-1 



•24765 



•24757 



•2B-|-05A-i-05B 



1970-3 



3304-2 



•29816 



•29820 



•2A+ 05A + -05B 



1970-3 



3310-9 



•29755 



•29748 



•2A + -2B 



1970-3 



24870 



•39613 



•39596 



•2A-L-2B+05A-I-05B 



1970-3 



1986-2 



•49601 



•49582 



* The decimal points are due to the fact that we have been using a B.A. box. 

 This box has been carefully calibrated, and the results expressed in legal ohms. 



The sensitiveness of adjustment in these observations 

 amounts to 5 M.M.F.^s, nevertheless we find that the ratio 

 of two capacities obtained on different days is nothing like so 

 consistent as the sensitiveness would lead us to infer that it 



