14 
ME. J. E. H. GORDON ON THE DETERMINATION OE 
This gives 
S(A)= 77488-8 sq. centims. 
Thus we obtain the following values for the area of the helix : — 
By Prof. Maxwell’s experiments with the great B.A. dynamometer — 
£(A)=77488-8 sq. centims. 
By Gordon’s experiments with small dynamometer (Gordon’s calculation) — 
^(A)=77280'5 sq. centims. 
By Maxwell’s calculation of Gordon’s experiments — 
5J(A)= 77554 sq. centims. 
Mean of the two calculations of Gordon’s experiments — 
S(A)=77417'2 sq. centims. 
Finally, 
2(A)={ 
Maxwell 
Gordon . 
77488 8 ) -|^ ean 77453.0 S q. centims. 
77417-2/ , H 
Calculation of the strength C of a current in the Helix in terms of the deflection l of the 
suspended magnet. 
Let 2 1 be the length of the suspended magnet, H the horizontal component of the 
earth’s magnetism, we have from (16) 
ml 
H ml tana=2(A) fg C 
H tan 
;(A) 
(19) 
Formula for a. 
a is the rotation expressed in circular measure corresponding to a difference of mag- 
netic potential equal to unity. Thus 
*=v, W ( 2 °) 
where Q is B expressed in circular measure, and V the magnetic potential at any part of 
the tube. 
The following formula gives the difference of the magnetic potentials at the ends 
L, M, due to a current C. 
