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VIII. On Diamagnetism. By M. Plucker. In a Letter to 

 Mr. Faraday. 

 Sir, 



I HAVE the honour to send you two small memoirs, which 

 on account of political circumstances have reached me 

 later than usual. I have already mentioned to you the first. 

 The second relates especially to diamagnetic polarity, which 

 is now placed beyond doubt. You will find, among others, the 

 curious fact, that the intensity of the diamagnetic force increases 

 more rapidly when the force of the electro-magnets is increased 

 than that of the magnetic force. The increase of the force of 

 the electro-magnet imparts to a piece of charcoal, having first 

 the position of a magnetic body, that of a diamagnetic body. 

 I have subsequently proved this law in different ways. The 

 following experiment is striking. If by means of a counter- 

 poise, any body containing at the same time magnetic and 

 diamagnetic substances (for instance mercury in a brass vessel, 

 this last being magnetic) is held in equilibrium, this body is 

 repelled by the magnet when brought near it, and attracted 

 when it is removed. 



I have devised a method which allows of my comparing 

 exactly the intensity of the diamagnetism of the different 

 bodies, solid and liquid, and at the same time I arrived at a 

 number of curious results concerning magnetic induction, and 

 especially the relation between the chemical constitution of 

 bodies and their magnetism. The difficulty of obtaining che- 

 mically pure substances presented the greatest obstacles. Thus, 

 for example, ^ per cent, of protoxide of iron mixed with a mass 

 of peroxide, ought at least to double the magnetism. The 

 magnetism of the oxides is increased by the acids which unite 

 with them to form salts. Supposing the magnetism of the iron 

 = 100000, I find that of a similar weight of oxide of nickel 

 (Ni) equal to 35, that of the same oxide in the state of hydrate 

 (Ni + H) equal to 142. The yellow ferrocyanide of potash is 

 diamagnetic; the red ferridcyanide, on the contrary (whether 

 in crystal or in powder, or in solution), is decidedly magnetic. 

 [A crystal of this last salt shows very clearly the repulsion of 

 the optical axes by the magnet ; without paying attention to it 

 one might easily take it for a diamagnetic body, &c] I have 

 examined equally the influence of heat. For mercury, sul- 

 phur, stearine, I have not observed the least difference, either 

 at a high or low temperature, whether in the liquid or solid state. 

 But bismuth gave very different results. In one of my expe- 

 riments, it required, at the ordinary temperature, 1*67 gramme 

 to counterbalance the diamagnetic repulsion of a mass of 14-4 

 grammes. At an elevated temperature, 0*28 grm., that.is to 



