Chemistry and Physics. . 271 



tical axes of magnetic and diamagnetic crystals, and the changes of 

 distance to the nature and laws of the attractions and repulsions exhib- 

 ited under the several circumstances detailed. — Sir W. S. Harris con- 

 sidered that the laws of magnetic forces in relation to the action of 

 magnets on each other, or a magnet on a mass of common iron, were 

 liable to vary, from the changes which arose in the amount of induc- 

 tive action of which the attracting bodies were susceptible. He had 

 shown, in a paper in the Edinburgh and London Philosophical Trans- 

 actions, that in electricity and magnetism the amount of inductive dis- 

 turbance was limited, — so that after a certain lime, under given condi- 

 tions, the disturbance became the greatest possible, and then the law 

 of the force changed ; and hence arose all the irregularities which had 

 embarrassed early inquirers into this subject. In fact, the force between 

 a magnet and a simple mass of iron varied in a simple inverse ratio 

 with the force induced in the iron and with the disturbance conjointly. 

 If either of them became constant, the whole force varied with the 

 other. If, therefore, it should happen that as the disturbance in the 

 iron approached a limit the changes were not uniform, then we obtained 

 irregular results. So long, however, as the induced force went on uni- 

 formly, we had the total or absolute force in the inverse ratio of the 

 squares of the distances. In the case of two magnets magnetized, or 

 nearly so, the force of attraction between them varied in the inverse 

 ratio of the simple disturbance, because the amount of the induced 

 force had been reached. On this principle it was found that in the re- 

 pulsive force between two magnets, the repulsive action at certain dis- 

 tances became changed into attraction ; and it is not an uncommon cir- 

 cumstance to find two magnets attract at one distance and repel at 

 another. These results he thought might be applied in explanation of 

 some of the phenomena now under consideration. The force of mag- 

 netic action might vary, whilst the diamagnetic force after all may have 

 been constant. 



Dr. Lloyd inquired if Pliicker had tried whether crystals with posi- 

 tive axes exhibited any difference in the laws of diamagnetic action 

 from those which had negative axes ? — Prof. Faraday replied, that Prof. 

 Pliicker had minutely investigated this point, and found no diversity of 

 law corresponding to this difference in optical structure. SirD. Brews- 

 ter inquired whether Prof. Pliicker had investigated the influence which 

 changes of temperature produced in the diamagnetic action of crystals? 

 kome of these changts, he conceived, were of such a nature as to 

 afford an admirable test whether the same circumstances in the corpus- 

 cular constitution of the crystal on which their optical characters de- 

 pended, were those which gave rise to their diamagnetic relations or 

 no *. For example, in some of the biaxal crystals, as sulphate of lime, 

 *hen heated, the axes approached, and at length coincided, — the crys- 

 tal becoming monaxal ; and by continuing the heating, they again sepa- 

 rated in a niane at right angles to the one in which they before lay. 

 Such a serfls of changes, he conceived, if examined in relation fo the 

 diamagnetic forces, might afford a test whether the curious properties 

 discovered by Prof. Pliicker had their origin in the chemical constitu- 

 tion of the bodies, or in that corpuscular structure from which their 

 optical properties originated. Prof. Pliicker replied, that he had not 







