Mr. G. Gore on the Magnetism of Electrodynamic Spirals. 267 



composed of thin iron wire 

 15 centims. long, and each of 

 the same thickness, were taken, 

 and one of them freely sus- 

 pended (by means of the two 

 fibres C, C) vertically and 

 facing the other at a distance 

 of about 2 or 3 millims. apart. 

 The lower ends of the spirals 

 dipped into two small cups of 

 mercury to enable the con- 

 nexions to be made with free- 

 dom of motion to the sus- 

 pended one ; and the similar 

 poles of the spirals faced each 

 other. The current from the 

 twelve Grove's cells in single 

 series was passed through 

 them; they immediately re- 

 pelled each other and then melted. The same current was now 

 passed through two similar ones 1*6 centim. in diameter, com- 

 posed of thicker iron wires, each 1.2 centims. long and *95 mil- 

 lim. thick; they repelled each other most distinctly and strongly 

 whilst warm, and also whilst quite red-hot, and the moveable one 

 instantly fell back on disconnecting the battery. 



As general results of these experiments on electro-spirals, it is 

 shown, first, that a red heat diminishes only the induced magne- 

 tism in an electro-spiral of iron, and does not increase or decrease 

 that due to the current alone; secondly, that a red-hot electro- 

 spiral of iron is capable of inducing magnetism, but not of having 

 magnetism induced in it; thirdly, that the production of heat 

 by electricity in a wire of great resistance, whether of iron, cop- 

 per, or platinum, is not attended by a diminished production of 

 the magnetism due to the current in the heated part of that wire. 



These results also support the view that the magnetism of an 

 electro-spiral of copper or other non-magnetic or slightly mag- 

 netic metal is not due to a particular position or mode of motion 

 of the particles of the metal, but is a direct result of, and inse- 

 parable from, the electric current itself; whilst that of a similar 

 spiral of iron is partly due to the same cause, and is partly de- 

 pendent upon a molecular condition which is destroyed by a 

 high temperature. 



The induced magnetism of iron is a much more complex phe- 

 nomenon than the magnetism of an electric current, because it 

 depends both upon temperature and upon the molecular struc- 

 ture of the iron ; whereas the magnetism of an electric current 



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