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LVI. On the Energy of the Amperian Molecule. By A. P. 

 Chattock, Professor of Physics, University College, Bristol, 

 and F. B. Fawcett, Associate of University College, Bristol*. 



THE following experiments were undertaken for the pur- 

 pose of determining, if possible, whether the molecular 

 currents of Ampere are accompanied by motions of the mole- 

 cules themselves. The}' were suggested during an attempt 

 by one of usf to express certain physical properties of solids 

 in terms of the ionic charges of their molecules. 



The theory put forward by Weber, that Amperian molecules 

 may be rotating charged carriers of electricity, lends itself at 

 first sight to the view that the molecules of all matter, whether 

 in the electrolytic form or not, carry upon them the charges 

 they possess when in the condition of ions. It is only neces- 

 sary to suppose that the molecules of a magnetic substance 

 rotate with these charges in virtue of their heat motions, to 

 account for the permanence of their magnetic moments at 

 any given temperature. 



Upon this supposition, if a bar of iron is saturated in a 

 magnetic field, and this field is suddenly strengthened, the 

 effect upon the iron will be two-fold. There will be a sudden 

 decrease in the magnetic moments of the molecules corre- 

 sponding to a decrease in their rates of rotation, and therefore 

 to a cooling of the iron as a w r hole ; and this will be followed 

 by a slow return to their original condition as the iron receives 

 heat from surrounding objects. 



The result of E wing's work on iron subjected to intense 

 fields has been to show that no certain alteration in the value 

 of I (the magnetic moment per cub. centim. of the iron) 

 can be detected after saturation within the wide limits of field- 

 strength which he employed. Upon the present hypothesis 

 there should be no permanent alteration ; and even the tem- 

 porary fall of I on the first application of the field would be 

 far too small to detect ; its value being about 5 x 10~ 1L I when 

 the magnetizing force is raised to 40,000 after saturation (see 

 below). 



But though the alteration of I is inappreciable, the accom- 

 panying fall of temperature is not ; and we therefore decided 

 to look for it. We were, moreover, encouraged to make the 

 experiment by the publication of an interesting paper on the 

 subject of ionic charges and their consequences by Dr. F. 



* Communicated by tlie Authors, 

 f Phil. Mag. Dec. 1892, p. 480. 



Phil. Mag. S. 5. Vol. 38. No. 234. Nov. 1894. 2 K 



