Brown — Mechanical Stress and Magnetisation of Nickel. 517 



2. With nickel, beyond a certain value of longitudinal magnetic field, 

 the twist increases with the load on the wire. 



With iron, in all fields, the twist decreases \\'ith the load. 



3. With nickel, the longitudinal magnetic field in wliich the maximum 

 twist occurs is independent of the hardness of the wire, but is different for 

 different loads. 



"Witli iron the magnetic field in which tlie maxiiQum t\7ist occurs is independent of 

 the load. 



4. With nickel, the curves obtained witli differently loaded wires, cross 

 one another in definite longitudinal magnetic fields, whatever the liardness 

 or length of the wire. 



With iron the curves never cross, whatever the load or length of the wire. 



5. Witli nickel, the longitudiual magnetic field in which the maximum 

 twist occurs is independent of the length of the wire, the load being constant. 



The same holds with iron wire. 



6. With nickel, the twist is directly proportional to the length of the 

 wire. 



The same holds with iron wire. 



7. With nickel, the longitudinal magnetic field in which the maximum 

 twist occurs is independent of the current density in the wire. 



"With iron it changes with the current density. 



8. With nickel, the twist is directly proportional to the current density 

 in the wire, wliether with different currents through tlie same wire or the 

 same current through wires of different diameters. 



The same holds with iron \\ire. 



9. With nickel vsdres of different oross-sectional areas, the maximum twist 

 occurs in tlie same longitudinal magnetic field. 



With iron the maximum twist takes place in different longitudiual magnetic fields. 



10. With nickel, when the cross-sectional area of the wire is increased 

 4'3 tim«s, the increase in the twist is larger the greater the longitudinal 

 magnetic field: thus, in afield of 13 units, the twist is increased 12-6 per 

 cent. ; in a field of 30 units, 16-7 per cent. ; and in a field of 50 c.g.s. 

 units, 19'3 per cent. 



With iron for the same increase in the cross-sectional area of the wire, the twist is 

 increased about 75 per cent, in a field of 14 c.g.s. units. 



11. Wlien the soft wires of nickel and iron (of the same length, 

 diameter, and under the same longitudinal load) are tested under the same 

 conditions, the maximum twist for nickel (95 mm.) occurs in a longitudinal 

 magnetic field of 13 units, and the maximum twist for iron (40'5 mm.) 

 takes place in a field of 2'5 c.g.s. units. 



