284 Prof. J. A. Ewing. [June 20. 



in a length of 40 cm. or so. It was then examined magnetically as 

 before, and scarcely a trace of creeping could be observed when a feeble 

 magnetising force was applied. When the compensating coil was 

 properly adjusted the making or breaking of the magnetising current 

 caused no more than a slight momentary quiver of the magnetometer 

 needle, followed by no measurable drifting, although the whole 

 magnetic effect (compensated by the coil) was equivalent to a 

 hundred or more scale divisions. When a magnetising force of as 

 much as 0*6 c.g.s. unit was suddenly applied, the amount of creeping, 

 if there was any, was certainly less than 1 per cent, of the immediate 

 effect. With values of p higher than this it became possible to detect 

 creep with certainty. The following notes relate to this wire : — 

 Magnetising force 



suddenly applied. Immediate value 



(c.g.s.) of 1 (c.g.s.). 



0- 75 4-49 



1- 28 8*42, crept in 1 min. to 8'58. 



2- 40 25-5 „ 26-4. 



These forces were in each case applied to this wire in a neutral state. 

 Another trial of the same, with feebler forces, gave 5*3 as the value 

 of d^/df^ for the immediate effect of a very small force, applied when 

 the iron was demagnetised. The same quantity in the annealed 

 specimen was, as has been said, about 10. In fig. 6 the relation of |f 

 (immediate) to p as stated above, is represented by the curve OR ; 

 the creeping up at the last point is US. 



In speaking of soft iron it has been shown that the effects of 

 creeping are most marked when a small addition 8 p is made to a pre- 

 viously increasing force p. In instances quoted above,, the creeping 

 up in 1 min. has under those conditions been many times greater 

 than the immediate effect of op. 



By way of putting the specimen of hardened iron to the same test, I 

 have applied a magnetic force of 1'46 and raised it by a small step to 

 1*49. The immediate effect of this step (which was balanced by the 

 compensating coil) was equivalent to twenty-two scale divisions of the 

 magnetometer, and this was followed during 1 minute by a creep- 

 ing equal to six scale divisions. In itself this creeping is consider- 

 able, but compared with the corresponding creeping in soft iron it is 

 extremely small. 



Pieces of steel (containing a good deal of carbon) have also been 

 examined, with the result that whether the steel be annealed or in its 

 commercial temper the phenomenon of creeping is even less visible 

 than in hardened iron. With annealed steel, a force which pro- 

 duced an immediate (compensated) magnetic effect equal to 124 scale 

 divisions caused barely a single scale division of creeping. With a 

 stronger current, giving an immediate magnetism of 340, the sub- 



