164 



Mr. T. Andrews. 



LMay 3, 



chemically upon it. I therefore made the following experiments 

 which demonstrate the interesting fact, that when a magnetised bar is 

 thus immersed a local galvanic current is set up between the polar 

 terminals and central equator or less magnetised portion of the bar, 

 the more magnetically-neutral zones acting electro-negatively in 

 relation to the poles. Under these induced conditions it becomes 

 obvious that a magnetised bar, forming one element of a galvanic 

 couple, would be more acted upon than an unmagnetised one, forming 

 the other element in the same solution. Hence, one explanation is 

 afforded of the electro-chemical positive position generally manifested 

 by the magnetised bar in course of the research. The experimental 

 demonstration of these local currents in a magnetised rod was con- 

 ducted as follows : — 



A pair of polished soft-iron bars, 6j inches long, 0*201 inch 

 diameter, cut adjacently from a larger rod, were each covered with 

 black india-rubber tubing, a small portion, one quarter of an inch at 

 each end of one bar (the flat disk at the end being coated with black 

 varnish) and half an inch in the centre of the other rod, being the 

 only portions exposed, and an equality of surface exposure being thus 

 obtained. The two rods were placed in the tube containing the 

 solution, and were connected in circuit with the galvanometer. The 

 tube containing them was placed in the coil, and on magnetising the 

 rods by means thereof, the rod whose polar terminals were exposed to 

 the action of the solution became electro-positive to the other bar. 

 Similar results were obtained when either a north pole or a south 

 pole was exposed singly as one element in connexion with a central 

 equator as the other. Many repeated experiments were made with, 

 apparatus shown on fig. 5, and about forty-six india-rubber-covered 

 bars were used in this part of the investigation. The results are 

 given in Table D (p. 166). 



Nitric Acid and Potassium Bichromate, Col. 3. — On ceasing to 

 magnetise the bar A in course of any experiment the galvanometer 

 deflections almost immediately fell to zero, and on again magnetising 

 the bar A deflections went up, the polar terminals resuming their 

 positive position. In this experiment the central equator had an 

 exposed surface of \ inch and each polar terminal \ inch ; another 

 experiment was made in which the exposed part of the central 

 equator was only ^ inch and each polar terminal g- inch ; the results 

 were the same though of less extent. Similar results were obtained 

 on ceasing at any time to magnetise the bars in the cupric chloride 

 solutions, Cols. 1 and 2, though less extensive. 



Nitric Acid and Potassium Bichromate, Col. 4. — On ceasing to 

 magnetise at end of any experiment, the deflections of the galvano- 

 meter fell some degrees ; but on re -magnetising, deflections rose 

 again, S. pole being positive. 



