H. A, Rowland—Absolute Unit of Electrical Resistance. 285 
and the deflection was diminished by its torsion 00132. No 
mention is made of the method used for untwisting the fiber, 
and we see that it would require only 2°11 turns to deflect the 
needle 1° from the meridian. To estimate the approximate 
effect of this, we may omit from Maxwell’s equation* all the 
other minor corrections and we have 
__GKw cos p =} a ae ft ) nearly, 
where we have substituted g—f for g in Maxwell's equation 
in the term involving 4 In this equation 7 is measured from 
the magnetic meridian; but let us take # as the angle from the 
point of equilibrium. en p’=g’+a and et ad where 
~’ and g’ are for negative rotation and #” and @” for positive 
1 
R=} 
rotation and a= are sin =— 
14+¢ 
Let ‘oa eect 
. —~ GKw 
Then CR 
= tan p(1+#)’ 
; 1 
CR ite 
; R=3(R'+R’). 
Where R’ and R” are the apparent values of the resistance as 
calculated from the negative and positive rotations, and R, is 
the mean of the two as taken from the table published by the 
British Association Committee. If R is the true resistance, 
1 | 
OR= oe 
sin a’ ‘ es 
tan @'(1-H0)(14 <) tan 9'(40(1~ in =) 
We shall then find approximately 
oS 1+ tan yp’ tana Be: —— — 
F sin a tana ii ei 
R14 sin 3) (1- tan yp" . (: sin p" ( a tan? 
When a is small compared with #” or y’, and when these are 
also small, we have 
RER(parat—W)tes) 
So that b¥ taking the mean of positive and negative rotations, 
the pedis of bortibs is almost entirely aiimpinated. Ne 
the angle by which the needle is deflected ge t = mag 
meridian by the torsion and its value is 3 (1-7) nearly, 
+ « Reports on Electrical Standards,” p. 103. 
1—tany” tana 
