MECHANICS AND RADIUM. 209 



to us animated with enormous velocities. We shall 

 see them in very different parts, and it is they that 

 explain for us the principal phenomena of optics and 

 of electricity. The brilliant synthesis about which I 

 am going to say a few words is due to Lorentz. 



Matter is entirely formed of electrons bearing enor- 

 mous charges, and if it appears to us neutral, it is 

 because the electrons' charges of opposite sign balance. 

 For instance, we can picture a kind of solar system 

 consisting of one great positive electron, about which 

 gravitate numerous small planets which are negative 

 electrons, attracted by the electricity of opposite sign 

 with which the central electron is charged. The 

 negative charges of these planets balance the positive 

 charge of the sun, so that the algebraic sum of all 

 these charges is nil. 



All these electrons are immersed in ether. The 

 ether is everywhere identical with itself, and perturba- 

 tions are produced in it, following the same laws as 

 light or the Hertzian oscillations in empty space. 

 Beyond the electrons and the ether there is nothing. 

 When a luminous wave penetrates a part of the ether 

 where the electrons are numerous, these electrons are 

 set in motion under the influence of the perturbation 

 of the ether, and then react upon the ether. This 

 accounts for refraction, dispersion, double refraction, 

 and absorption. In the same way, if an electron was 

 set in motion for any reason, it would disturb the 

 ether about it and give birth to luminous waves, and 

 this explains the emission of light by incandescent 

 b(yiies. 



In certain bodies — metals, for instance — we have 

 motionless electrons, about which circulate movable 



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