316 LORD RAYLEIGH AND MRS. H. SIDGWICK ON THE ABSOLUTE 
§ 28. The results given in these tables are the effective resistances required to 
obtain a balance, expressed in terms of the B.A. unit. To reduce them to absolute 
measure we must multiply by 10 9 , and by a factor, which we may call x, expressing 
the absolute value of the B.A. unit in terms of 10 9 , and which it is our object to 
determine. 
The actual value of the same quantities in absolute measure is found by multiply¬ 
ing the coefficients of induction (M—M 0 ) already given (§ 25), by the number of 
turns in the coils 1588, and by the number of revolutions per second. 
In the first series the frequency of vibration (f) of the electric tuning-fork was in 
the standard case (see Appendix) 
/=£(128*140+£&)=£X 128-407 
and the number of revolutions per second is equal to 2/A-10. In the second and 
third series 2/=129'340, a number which in the second series is to be divided by 16, 
and in the third series by 10, in order to obtain the number of revolutions per second. 
The equation to determine x is thus for the first series of observations 
214-569 X 1588 X 12-8407=a:X '00443407 X 10 9 , 
whence 
$=•98674. 
From the second series 
214-569 x 1588x 129 340 
*= 16 x 10 9 x -00279 1 57 =' 98669 
From the third series 
110-392 x 1588x 129-340 
10 xl0 9 x-00229762 ~' 98 ° 83 
These are the final results already considered in § 21. 
Appendix. 
Frequency of Vibrat ion of Standard Fork. 
All our measurements, both by this method and by that of the revolving coil, being- 
dependent upon the pitch of a standard tuning-fork, we have considered it advisable 
to determine this element afresh. As in the first determination,'" a fork vibrating 
about 32 times per second rendered intermittent an electric current, which, passing 
* Proc. Roy. Soc., May, 1881, p. 137. 
