1911-12.] Transverse Induction Changes in Demagnetised Iron. 301 
necessary may be conveniently performed. The revolving reverser and 
rheostat are used to demagnetise the iron. 
Each exploring coil could, as required, be connected in series with a 
calibrating coil in the known field of a long solenoid and a Broka galvano- 
meter arranged ballistically. When used with the coil of 600 turns without 
resistances 1 mm. scale division = one-third of a C.G.S. unit of induction 
(B l ) in the steel tube. 
F urther data are as follows :■ — 
Length of experimental steel tube . 
33 
cms. 
Average thickness of shell .... 
. -0646 
cm. 
Average radius (to middle of shell) 
1-56 
cms. 
Sectional area of steel enclosed by — 
(1) 10 turns exploring coil measuring circular 
induction B c . 
0 399 sq. 
, cm. 
(2) 30 turns exploring coil measuring longi- 
tudinal induction, B L 
0’633 sq. 
cm. 
(3) 600 turns exploring coil measuring trans- 
verse (longitudinal) induction change, bB L 
0-633 sq. 
. cm. 
Value of circular field at radial distance of 1*56 cms. from axis of 
steel tube : — 
Per wire per ampere . . . H c = 0128 C.G.S. units. 
Per 37 wires per ampere . . H t . = 4'74 „ „ 
Per 36 wires per ampere . . . H c =4’61 „ 
Value of longitudinal field due to solenoid, the 6 strips being in series, 
H l = 4*61 C.G.S. units. 
Demagnetised Iron. 
(1) Experimental. 
The magnetic quality of the drawn steel tube is indicated by the 
following measurements of a hysteresis loop many times repeated. 
H. B. 
At cyclic extremes ...... 35 14,000 
Residual magnetisation ..... 0 10,600 
Coercive force ...... 6 0 
The continuous line curves of fig. 4 show the transverse (longitudinal) 
induction changes dE h which occur when the circular field H c is increased 
by increments from zero to a maximum, the steel tube having been 
