COMPLEX STRESS DISTRIBUTIONS IN ENGINEERING MATERIALS. 199 
permanent magnetisation, it is conceivable that the mechanism involved, 
whatever precisely it may be, is the same for both mechanical and magnetic 
hysteresis ; or (c) a combination of these two. 
Most frequently this aspect of the subject has been studied by observa- 
tion of the torsional oscillations of wires. The decrement of oscillations 
appears to be increased by : 
Temperature above atmospheric (36, 38, 37). 
Temperatures below — 80° C. for gold and magnesium (38), or — 40 for 
gold (36). 
Very high frequency oscillatory discharge (20). 
It is decreased by : 
Temperatures below atmospheric. 
In No. 36 this decrease is found for copper, platinum, silver, and 
steel; gold having a minimum at — 40° C. 
In No. 37 this decrease is found for silver, iron, and more especially 
aluminium; magnesium and gold having a minimum 
at — 80° C. 
(Exceptions are noted above.) 
Magnetic field, particularly alternating (34, 19, 20). 
Oscillatory discharge (34, 19, 20). 
(34 is concerned with tensile hysteresis.) 
On the other hand (12), successive torsions decrease the magnetisation 
in a given field. 
A relation between the decrement and the maximum strain is not in 
most cases available, but would be desirable from the point of view of 
answering the above inquiries. A glance at this summary suggests, how- 
ever, that the analogy between mechanical and magnetic hysteresis (0) 
finds some support. An important limitation is, however, suggested by 
the fact that whereas an alternating magnetic field tends to diminish the 
energy absorbed in mechanically straining (19, 20), yet, on the other hand, 
repeated torsion causes an increase in the energy required for magnetisa- 
tion (12). 
The suggestion should be regarded rather as a basis for investigation, 
than as based upon existing data. 
BIBLIOGRAPHY ON ALTERNATING STRESS. 
Drawn up by W. Mason and Dr. F. Rocers. 
1 Arnold, J. O. 1903 Dangerous Crystallisation of Mild Steel and Wrought 
Tron. (Description of Main Features of Arnold’s 
Alternate Bending Machine.) ‘Inst. C.E. Proc.,’ 
154. Supplement, 1903. 
2 Arnold, J. O. 1904 Fracture of Structural Steels under Alternating Stress. 
‘ Brit. Assoc. Report,’ 1904. ‘Science Abs.,’ 1904, 
Nos. 19298, 27958. 
Some preliminary experiments indicated that the resistance of structural 
steel to cycles of stress with considerable overstrain was inversely as the 
rate of alternation. 
3 Arnold, J. O. 1908 Factors of Safety in Marine Engineering. ‘ Inst. 
Naval Arch.,’ L., 1908. 
An analysis of ‘factors of safety ’ for various purposes is given; and 
the practical importance of the Wéhler phenomenon shown. 
The author demonstrates that the Wohler test does not detect brittle- 
ness—a, fact now accepted. He argues that the Wohler limiting stresses 
