Soft Iron, especially with weaker decomposing -powers. 45 



We see that here also observation and calculation do not di- 

 verge too widely. 



Before I leave the experiments with ellipsoids and pass to ray 

 own investigation, I must mention a still more recent work 

 (1870), that of M. Riecke*. He has observed, according to 

 Weber's method, the remagnetizing of various ellipsoids by the 

 vertical component of terrestrial magnetism. The more length- 

 ened the ellipsoid, the greater was, in general, the number re- 

 sulting for k. In conformity with the foregoing, this was to be 

 expected — since, X remaining equal, the quantity R increases 



simultaneously with ^, — although M. Riecke is more inclined to 



seek another reason for it. The magnetizing-force was not mea- 

 sured directly ; but if we assume, with Weber, that the vertical 

 component of the earth's magnetism (at G6ttingen)was = 4'228t, 

 then it follows that, for Riecke's experiments, R = , 31-0'72. 

 Corresponding to this, k increased from 13*5 to 25*4. 



It seemed to me not without interest to ascertain the magne- 

 tizing-function by another method, recently proposed by Kirch- 

 hoffj. Therein I experimented especially with feebler decom- 

 posing forces, in order once more to establish and place beyond 

 doubt the ascending course of k with such forces. The experi- 

 ments which I will communicate appear also to have a further 

 interest. The only case of magnetizing theoretically solved com- 

 pletely, and which at the same time can be carried out in prac- 

 tice, was till quite recently that of an ellipsoid (inclusive of the 

 sphere). In the present experiments, I believe, the theory is 

 for the first time tested on a body of another form, namely a ring. 



We imagine a ring of iron — that is, a solid of rotation which 

 is not touched by the rotation-axis. Let this ring, in its whole 

 periphery, be wrapped round with wire (the primary wire), and 

 let another wire (the secondary wire) be wound round it once or 

 more times. If a constant current is passed through the first 

 wire, and if the second is closed upon itself, a momentary cur- 

 rent is induced in the latter as soon as the direction of the pri- 

 mary current is suddenly reversed §. The integral value of the 



* Die Magnetisirungszahl des Eisens fur schwache magnetisirende 

 Krafte: Gottingen, 1871. Abstract in Pogg. Ann. vol. cxli. p. 453. 



t This number belongs properly to the middle of the year 1870. See 

 Weber, " Bestimniung der erdmagnetischen Kraft in Gottingen," p. 30 

 (Abhandlungen d. k. Gesellschaft d. Wiss. zu Gottingen, vol. vi.). 



% Pogg. Ann. Ergzbd. v. p. 1. 



§ I always employed the reversal of the current, because thereby the 

 results are less vitiated by residual magnetism than with the closing and 

 opening of the circuit. The same method was made use of by Weber and 

 v. Qu. Icilius. The employment of both methods would enable us to mea- 

 sure the residual magnetism of the iron. 



