PLtJCKER ON THE THEORY OF DIAMAGNETI8M. 339 



in the amount of the inducing force diamagnetism increases more 

 quickly than magnetism P^ 



26. I see the cause of this empirical law in the circumstance, 

 that to the excitation of the diamagnetic condition a greater 

 resistance is presented than to the excitation of the magnetic con- 

 dition. I will in the first place endeavour to illustrate this way 

 of regarding the subject by an analogous experiment, and then 

 endeavour to show how one of the experiments which I have 

 already described presents a new support to our assumption. 



27. A different resistance, such as we assume to exist in the 

 case of magnetic and diamagnetic bodies, is a proved fact as regards 

 many kinds of iron and steel, being in this case named coercive 

 force. This in general is deduced from the circumstance, that 

 some of these substances retain a greater quantity of magnetism, 

 and for a greater time, than others. But we can also establish 

 experimentally tliis difference as regards coercive force in the 

 different strength of the magnetism excited by induction, and 

 which afterwards quickly disappears. 



For this purpose let two equally long bars of hardened steel 

 and soft iron, the former of which is thicker than the latter, be 

 tied together at the middle, so that they form any angle, say one 

 of 45° with each other, and let them be suspended horizontally 

 (Plate V. fig. 6). If the system be caused gradually to approach 

 the pole of a strong magnet, at a great distance a position will 

 be assumed from which we may infer the predominance of the 

 attraction of the bar of iron, but when we approach the pole 

 the position assumed shows us that the bar of steel is the most 

 strongly attracted . At a great distance the bar of iron sets axial, 

 while near the pole the bar of steel takes up this position* 

 Instead of causing the system of the two bars to approach the 

 magnet, we could also, by choosing a suitable distance, change 

 the strong pole for a weak one, and thus obtain the corresponding 

 action. 



In this experiment, the steel, on account of its greater coerceive 

 force, is magnetized with more difficulty than the sofl iron. If 

 we assume that the diamagnetic coal assumes the magnetic 

 condition with more difficulty than the iron particles uniformly 

 distributed throughout its mass, then in a mixture of proper 

 proportions a bar of such coal must appear magnetic or diamag- 



