Ferromagnetic Wires by Magnetization. 



339 



tension. B. Brackett*, Gr. Klingenberg f , K. Tangli, have 

 also investigated the same subject, and obtained results similar 

 to those of Bidwell. 



In Bidwell's experiment, which is generally regarded as 

 the most reliable, the wire to be tested carried the mag- 

 netizing coil with it, so that even the smallest tension was 

 greater than 3 kilog. per square millimetre. Hence the 

 effect of small loading, which is remarkable in nickel, was 

 not well studied. The sensibility of his apparatus cannot, 

 moreover, be considered as sufficiently delicate at the present 

 day. It was, therefore, thought desirable to repeat his ex- 

 periment with an arrangement giving higher accuracy. 

 Besides iron and nickel we also examined nickel-steels kindly 

 placed at our disposal by Dr. Ch. Ed. Gruillaume, which 

 showed a remarkable anomaly with regard to the change of 

 length and of volume. 



2. The apparatus used in the present experiment is in 

 principle the same as that of Prof. Nagaoka. The chief 

 difference consists in using a rotating cylinder § to cause a 

 reflecting mirror to turn through a minute angle, instead of 

 three-pivots system. 



Fig-. 1. 



^%«%^ ////////M 



Wi 



:sz 



B M 



n-oi-n 



B 



ft 



_ ..£?* 



1 



& 



d> 



Fig. 1 shows the front and side views of the apparatus. 

 C is the magnetizing coil and AV the wire to be tested, whose 

 upper end is clamped to the support S, while its lower end 

 carries a weight Q. M is a reflecting mirror fixed to the 



* Brackett, Phys. Rev. v. (5) p. 275 (1897). 



t Klingenberg, Inaug. Diss., Berlin, 1897 ; Beibl. xxi. p. 897 (1897) ; 

 Inaug. Diss., Rostock, 1899 ; Beibl. xxiii. p. 270 (1899). 



§ K. Tangl, Ann. der Phys. vi. p. 34 (1901). 



|| Hertz, Instrumentenkunde, iii. p. 17 (1883) ; Gesammelte WerJce, 

 Bd. i. p. 227. 



