106 Potts — Rowland's JVeiv Method. 



ISTow, since in any case the last three terms are small, and 

 (1 — b'cV) and (1 — JVL) are nearly one, they may be dropped 

 from the last terms and we have 



C~ (\-b*cl) ~ + c b +(R »- R ») 6cL (15) 



Investigation — The arrangement is the same as in fig. 2. 

 In position a and with a resistance in arm 4, electric absorption 

 can be found. In position b and with a coil L in arm 4 in place 

 of the resistance, the capacity of the condenser can be com- 

 pared with the standard coil L. In formula (13) R includes 

 not only the ohmic resistance of branch a, but also the added 

 resistance due to electric absorption. 



A preliminary investigation was carried out to find whether 

 the correction due to the capacity of the coil C were appreci- 

 able and, if so, to ascertain its amount. 



The method chosen was as follows : An arrangement was 

 made as in fig. 2, except that in place of the condenser C the 

 coil L with which the capacity of the condenser is to be com- 

 pared is placed in arm 1 of the bridge. The arrangement was 

 first balanced with a direct current ; and the value of Kj as 

 measured and as calculated from R 2 , R 3 , R 4 were the same. In 

 Table VIII are given the results for E/j as calculated for three 



r=4810 Coil A = 5'3 henry 

 Date R 3 R x R\ T D=R' 1 -R 1 









Table VIII. 





R 2 = 



:1010 



R 4 = 



:912-5 





R 3 



Ri 



R'i 



T I 







By 



formula 13 



1 



4080 



224-6 



225-8 



•0188 



2 



4092 



224-8 



225'2 



•0488 



3 



4074 



225-0 



220-2 



•0182 



4 



4034 



225-0 



228-4 



•0182 



•20 4080 224-6 225*8 -0188 1-0 



•4 

 1-2 



3 - 4 with "01 microfarad 

 in parallel with coil. 



If formula (15) is used in calculating R'i it is 2262. Hence D=l - 2 as with- 

 out condenser. 



periods of the current. In all three cases B/ x is greater than 

 E-! by an amount D. A third observation was made with a 

 condenser of •01 microfarad capacity shunted across the termi- 

 nals of the coil. The corrected formula (7) was tested in this 

 way. The result gives the same value of D, with or without 

 the condenser, thus verifying the formula. By assuming the 

 quantity D as entirely due to the electrostatic action of the 

 coil, which if not absolutely true, the formula will at least give 

 a value of c' the equivalent capacity of the coil, which may be 

 used as the limiting value. The value of c' is *006 micro- 

 farad. In formula (15) the last term will be very small as 



