170 REPORT—18683. 
c=depth of section in the plane of the coil ...... = ‘0132 metre. 
b'=distance of mean plane of coil from axis of 
AO LOM Set: ins: dis shor aatard aed) ees CR — a 
a=angle subtended at axis by radius of coil=83° 1’, 
cos a= ='12245 ; 
2 
Then Garna(1 +75 5a) 
K=2" ee ii: 4 i fQ-15 sin® qos" 2) 
te A a cos” 4 —3 sin® ol, 
GK=7nl sin’ a { 1+i fy 2hS ©'sin?acos ta — =o sin? al. 
If the dimensions of the en are eit in metres, GK will be ex- 
pressed in metres. 
Let T be the time of 100 revolutions of the coil, expressed in seconds, then 
Tw =200n, 
or oe OOF 
Let D be the distance of the scale from the mirror, 6 the scale-reading mea- 
sured from the point of the scale which is nearest to the mirror, then 
tan 292 ; 
1 D 1 & 
‘Saag s tap}: 
To determine MHr, the coefficient of torsion, let the magnet be turned 
round so as to twist the fibre nearly 360°. Let the difference of reading due 
to the torsion be 4’, then 
the = il 
r= 4aD ‘i af 8 
4D 
To determine KM let the suspended magnet A be removed, and let another 
GH’ 
magnet, which we shall call B, be put in its place. Let the magnet A be now 
placed east or west of B, at a ‘distance equal to the mean distance of the coil, 
or Va?+b", Let the deflection of B when the north or south end of A is 
directed to it be », then 
M 
Gut fe 
The determination of the quantity L, the electromagnetic capacity of the 
coil, requires a more complex calculation which must be explained separately. 
In the actual experiment the deviation @ was always small, and therefore 
tan* # was very small, so that the term depending on L was never important. 
We may now write the value of R, 
Hi 2007? Dual sin’ a 
Ts { t 55 corrections}, 
