Q6 Prof. G. Wiedemann's Magnetic Researches. 



In order to investigate whether this phenomenon occurs 

 only with the first increasing and decreasing magnetizations 

 of the bars, or whether it occurs also after they have attained a 

 permanent condition after repeated action of the magnetizing 

 forces, the following experiments were made, in which freshly 

 heated iron bars were magnetized by currents passed round 

 them in such a way that their intensity could be gradually 

 increased up to a certain magnitude and then gradually 

 reduced to zero, so avoiding the influence of all disturbing 

 induction- currents. 



For this purpose a special regulating Bunsen's element 

 was employed (fig. 11). It consisted of a porcelain cylinder 

 36 centim. high and 10 centim. wide, on the bottom of 

 which was cemented a second concentric porcelain cylinder 

 closed at the top, 25 centim. high and 5 centim. wide. This 

 supported a porous cell 10 centim. high and 5 centim. wide, 

 in which was contained a Bunsen carbon-cylinder provided 

 with a connecting wire, and was filled with nitric acid. It 

 was surrounded by a cylinder of amalgamated zinc 10 centim. 

 high and 9 centim. wide, which was suspended by means of 

 strips of zinc soldered to it from the edges of the outer 

 porcelain cylinder, which contained dilute sulphuric acid. A 

 glass tube 40 centim. long closely surrounded the porous cell 

 and its support, and could be raised or lowered by means of 

 a cord attached to it, which passed over a pulley to a roller and 

 handle. A brass band stretched by a weight pressed against 

 the roller and held it firmly in any position. By this arrange- 

 ment the current could be increased from nearly zero up to 

 a considerable strength. Of course the same arrangement 

 might be employed as a Daniell cell*. 



The current from this cell was passed through a copper- 

 wire spiral 25 centim. long, 2*7 centim. internal diameter, 

 and 7 centim. external diameter, lying horizontally magnetic 

 east and west, 50 centim. distant from the steel mirror of the 

 reflecting-galvanometer. The deviation thus produced was 

 compensated by means of the vertical copper ring placed in 

 front of the mirror. A freshly heated bar of soft cast steel, 

 24 centim. long and 1 centim. thick, was fixed in the spiral, and 

 its momentum determined from the deflection of the mirror. 

 The corresponding intensity of the current was determined 

 as before, by turning down the ring. In order, further, to 

 be able to adjust the current during the temporary magneti- 

 zation of the bar to any desired strength, the ends of the 

 spiral were connected, in particular cases, with the quadrants 



* Meanwhile a similar arrangement has been described by Stebbins, 

 Centralbz.f. Opt u. Mecli. iv. p. 119 (1883) ; Beibl. yii. p. 474 (1883). 



