1894.] Effect of Mechanical Stress, $-c., on certain Alloys. 103 



off by the succeeding wave of negative charge, which, as is well 

 understood, opens the leak. The time of an alternation is, however, 

 quite insufficient to produce any such effect on the water-pipe earth, 

 and, in consequence, the net result is a passage of negative electricity 

 to earth through the cables, and of the corresponding positive quantity 

 to earth by the water-pipes. 



The maximum effect that has been observed so far amounts to an 

 apparent E.M.F. slightly exceeding 10 volts, with the eleven circuits 

 connected to one machine, but it appears that a greater effect would 

 be produced by still further increasing the length of mains in con- 

 nection. 



IV. " The Effect of Mechanical Stress and of Magnetisation on 

 the Physical Properties of Alloys of Iron and Nickel and of 

 Manganese Steel." By HERBERT TOMLINSON, B.A., F.R.S. 

 Received May 7, 1894. 



(Abstract.) 



The author has examined the principal physical properties of three 

 alloys of nickel with iron and of the non-magnetic manganese steel 

 of Mr. Hadfield, together with the effects of mechanical stress and 

 magnetisation on these properties. The three nickel-iron alloys con- 

 tain 22, 25, and 30 per cent, of nickel, and are designated Specimens 

 D, E, and F respectively ; they are in the form of thin wires, and 

 similar specimens have been previously tested by Dr. John Hopkinson 

 for the effect of change of temperature on their magnetic pro- 

 perties.* Specimen F practically loses its magnetic susceptibility at 

 a temperature below 100 C., but regains it again on cooling to the 

 temperature of the room. Specimens D and E are magnetic in the 

 hard-drawn condition, but become non-magnetic when heated above 

 600 C. They do not, however, like Specimen F, regain their mag- 

 netic susceptibility when cooled to the ordinary temperature of the 

 room, but can be made to do so, either by the process of wire-drawing, 

 or by cooling them a few degrees below C. Tables I andJI contain 

 the values of the principal physical constants of the three nickel-iron 

 alloys, of Hadfield's non-magnetic manganese steel, and of nickel and 

 iron. The former of these two tables relates to the substances in the 

 hard-drawn condition in which they were received by the author, 

 and the latter to the same substances after annealing, so that by a 

 comparison of the two tables, the effects of the permanent strain 

 resulting from wire-drawing may be seen. These effects are in some 

 instances of the same nature for the nickel-iron alloys as for nickel 

 and iron. Thus the density of all the specimens is diminished by 

 * ' Roy. Soc. Proc.,' vol. 48, pp. 113. 



