Force of Magnetization. 295 



ders of soft Norway iron i cm long and 4 mm in diameter. These 

 were placed horizontally in the solution and were attached to 

 the end of copper wires. The wire was in each case thoroughly 

 insulated from the liquid, and the iron bar itself was protected 

 by a coating of wax with the exception of a single portion of 

 its surface, which to the extent of a few square millimeters 

 was exposed to the action of the liquid. Under these condi- 

 tions, the direction of the electro-motive force developed be- 

 tween the terminal within the field and a similar one outside 

 was found to depend upon the portion of the bar exposed and 

 the position of the latter with reference to the lines' of force. 

 Whenever the exposed surface was in the neighborhood of an 

 induced pole within the soft iron electrode it became in its re- 

 lations to iron outside of the field, as zinc to platinum. When- 

 ever on the contrary the exposed surface was situated in a 

 neutral portion of the bar, it became as platinum in its rela- 

 tions to unmagnetized iron. When platinum, carbon or cop- 

 per was substituted for the unmagnetized electrode the 

 electro-motive force of the cell thus formed was increased by 

 magnetization, in the case in which a pole of the iron terminal 

 was exposed to the liquid and diminished by magnetization 

 when the surface acted upon lay in the middle of the bar. A 

 reversal of direction in the current flowing between such a bar 

 of iron in the field, one end of the bar being exposed to action, 

 and an unmagnetized iron terminal, could be produced by turn- 

 ing the former in the held. When the axis of the bar was 

 parallel to the lines of force and it was accordingly magnetized 

 longitudinally, it acted as a zinc pole, the current flowing from 

 its surface through the cell to the unmagnetized electrode. 

 When turned through 90° upon an axis perpendicular to the 

 line joining the poles of the electro-magnet, the bar became 

 magnetized transversely and the direction of the current was 

 reversed. 



Between bars lying with their axes parallel -to the lines of 

 force, the end of one and the middle of the other of which 

 was exposed, the effect was more marked than between either of 

 them and a piece of unmagnetized iron ; the bar with exposed 

 pole acting as zinc, that exposed in the middle as platinum. 



After having determined the conditions which govern the 

 direction of the current, we turned our attention to the rela- 

 tion between the strength of the magnetic field and the electro- 

 motive force which it is capable of producing. The cell 

 selected for this work was an iron-platinum element, contain- 

 ing a solution of potassium bichromate in dilute sulphuric acid. 

 In this liquid the electro-motive force of magnetization was so 

 marked that when the cell was placed between the pole pieces 

 of the electro-magnet the influence of the residual magnetism 

 of the latter upon its electro-motive force could easily be de- 



