74 
MESSRS. G. F. C. SEARLE AND T. G. BEDFORD 
The wire was placed horizontally, perpendicular to the magnetic meridian, and the 
tension was applied by a flexible silk cord which passed over a pulley and supported 
a weight. The reversing key described in § 30 was used, the current being measured 
by a shunted d’Arsonval galvanometer. We satisfied ourselves by the comparison 
of the values of W found (1) from cyclic B—H curves, (2) by the electro-dynamo- 
meter, that the method was yielding at least approximately exact values of W. 
Before the observations corresponding to any given value of Hq were made, the wire 
was subjected to several cycles of loading and unloading, the maximum load being 
24 kilogrammes. The magnetic observations were taken only as the load was being 
increased. The section of the wire was *00708 scp centim., so that a load of 1 kilo¬ 
gramme gives a tension of 1*39 X 10^ dynes per sq. centim. The results are given in 
the following table and in fig. 7. (See also § 67.) 
Observations on a soft iron wire during both loading and unloading showed that 
the curves for loading and unloading are not quite identical, though the difference 
between them is not large. 
