104 Mr. H. Tomlinson. The E/ect of Mechanical [May 31, 



wire-drawing, the simple rigidity is also diminished, and the internal 

 molecular friction, as inferred from the logarithmic decrement of arc 

 of torsionally oscillating wires, is considerably increased. On the 

 contrary, whilst the specific resistance of iron, nickel, and man- 

 ganese steel is increased by wire-drawing, that of the iron-nickel alloys 

 is largely diminished. Again, whilst wire-drawing largely decreases 

 the magnetic permeability of iron, nickel, and iron alloyed with 

 30 per cent, of nickel, it makes the alloys containing 22 and 25 per 

 cent, of nickel to considerably appreciate in permeability, and, in 

 fact, in a great measure transforms them from the almost non-magnetic 

 to the magnetic condition. Dr. John Hopkinson has shown that a 

 similar result can be obtained by cooling the alloys several degrees 

 below C. The magnetic properties of manganese steel cannot, 

 however, be restored by the process of wire -drawing. 



As regards the physical properties themselves, apart from the 

 effects of stress or strain on these properties, all the nickel-iron alloys 

 here examined have considerably less longitudinal and torsional 

 elasticity than the pure metals nickel and iron ; they also have con- 

 siderably less internal friction. This last is very conspicuously 

 the case with the alloys containing 25 per cent, nickel, which in 

 the annealed non-magnetic condition has an internal molecular 

 friction less than one-fourth of that of iron or nickel. For mag- 

 netising forces extending from 0'8 to 2 C.G.S. units, the alloy con- 

 taining 30 per cent, of nickel is possessed of much greater magnetic 

 permeability than iron, but for large forces the iron is superior. The 

 other two nickel-iron alloys are, when in the annealed condition, 

 almost as non-magnetic as Hadfield's manganese steel. 



The temporary effects of longitudinal mechanical traction and 

 magnetic stress on some of the physical properties are exhibited in 

 Table III. It will be noticed that longitudinal traction produces on 

 both the specific resistance and the thermo-electric height of the 

 alloys of nickel with iron, an effect which is intermediate to that pro- 

 duced on the pure metals nickel and iron. The magnetising forces 

 employed ranged for the most part between 40 and 80 C.G.S. units, 

 and the results obtained refer only to the elastic effects of the force, 

 which effects are approximately proportional to the force itself. These 

 elastic effects are much greater in proportion to the change of mag- 

 netic induction than are the residual effects. The change of both 

 specific resistance and thermo-electric height produced by a C.G.S. unit 

 of magnetic stress, is in all cases enormously greater than that pro- 

 duced by a C.G.S. unit of mechanical stress. 



The effects of mechanical stress on the magnetic permeability of 

 all the different iron-nickel alloys are fully exhibited in this paper. 

 Speaking roughly, they lie between the corresponding effects for the 

 pure metals iron and nickel. 



