28 
MR. J. E. H. GORDON ON THE DETERMINATION OF 
Let t the adopted standard temperature be that of K (4), which, being the lowest in 
either set, will make all the terms positive. 
The following are then the values of q 0 : — 
K (1), £ 0 =-000178(51 0 -4 — 40°- 3) -j--000000596(51°-4—40 o -3) 2 = -0020492. 
Similarly : — 
K(2) . 
. £ o =-0023181 
P(l) . 
. ^=-0029908 
K(3) . 
. ,,=-0022988 
P(2) . 
. „ =-0023420 
K(4) . 
. „ = 0 [standard] 
P ( 3 ) • 
. „ =-0022988 
K(5) . 
. ,,=-0003586 
P ( 4 ) • 
. „ =-0026654 
K (6) . 
. „ =-00051895 
P ( 5 ) • 
. „ =-0028942 
Torsion of the Suspending Thread. 
We require the ratio of the force of torsion to the magnetic directive force. 
The Kew formula is (changing the notation to suit the letters commonly used in the 
C.G.S. system) 
T U° 
90° — m 0 ’ 
where r is the force of torsion and u° is the change of declination produced by a twist 
of 90° in the torsion-thread. 
As the magnet was not suspended from a torsion-circle, the only twist that could be 
applied was +n (360°) given by twisting the magnet completely round in a + direction. 
If, however, which for so small a correction as this is we may do, we assume that the 
change of declination produced by a twist of 360° is 4 times that produced by 90°, the 
formula still holds, only we must substitute 360° for 90° in the denominator ; we have 
then 
H m 360 ° — m oS 
(28) 
where u° is now the torsion produced by 360° of twist. 
The following observations were made, the first by reading the scale when the 
magnet was at rest, the others by taking the limits of swing after stopping the magnet 
as nearly as possible by means of a magnetized penknife : — 
