RELATIONS TO OTHER SCIENCES 155 



2. If the resulting motion of the molecules is not zero, the initial 

 diamagnetic modification is followed by an orientation of the mole- 

 cules under the action of the external field, which cause a para- 

 magnetism to appear that masks the underlying diamagnetism, the 

 new phenomenon being considerable compared to the first, when the 

 symmetry permits it to appear. 



In slightly paramagnetic bodies, such as gases, the heat agitation 

 is opposed to the complete orientation of the molecular magnets, to 

 saturation, and one finds, in seeking what permanent condition is 

 established, the law of Curie, that the variation of paramagnetic 

 constants is in inverse ratio to the absolute temperature. 



3. Finally, the change of period of revolution in consequence of 

 the diamagnetic modification corresponds to the Zeeman effect, as 

 general as diamagnetism itself; iron, certain rays of which show the 

 Zeeman effect, is diamagnetic before the orientation of the molecular 

 magnets under the action of the external field makes it appear para- 

 magnetic. 



The orbits considered, which represent the molecular currents of 

 Ampere, are also the circuits of zero resistance of the diamagnetism 

 of Weber, with this remarkable peculiarity that the flux which passes 

 through them is not constant, as Weber supposed, if the inertia of the 

 electrons is entirely of electromagnetic origin. 



I have shown, on the other hand, that the orbits of the electrons 

 supposed circular, and described under the action of central forces, 

 experience no deformation during the diamagnetic modification, this 

 latter consisting only in a change of velocity of the electrons in their 

 orbits. We can thus form an exact and simple conception of the facts 

 of magnetism and diamagnetism by considering the molecular cur- 

 rents as non-deformable but movable currents, of zero resistance and 

 of enormous self-induction, to which all the ordinary laws of induc- 

 tion are applicable. 



XI. Conclusion 



The rapid perspective which I have just sketched is full of pro- 

 mises, and I believe that rarely in the history of physics has one had 

 the opportunity of looking either so far into the past or so far into 

 the future. The relative importance of parts of this immense and 

 scarcely explored domain appears different to-day from what it did 

 in the preceding century: from the new point of view the various 

 plans arrange themselves in a new order. The electrical idea, the 

 last discovered, appears to-day to dominate the whole, as the place 

 of choice where the explorer feels that he can found a city before 

 advancing into new territories. 



The mechanical facts, the most evident of all those of which matter 

 is possessed, from the first attracted the attention of our ancestors, 



