RELATIONS TO OTHER SCIENCES 149 



where the acceleration is sufficient for it to radiate an appreciable 

 energy to a distance by means of the acceleration wave, it is probably 

 necessary to bring in, by other terms in the equation of motion of the 

 electron, some forces by which it can receive again the energy which 

 it radiates, and which disappear in the case of quasi-stationary 

 motion. It does not seem, however, in any experimental case that 

 these corrective terms can become appreciable. 



From the same point of view, the electrons in periodic motion in the 

 material atom are necessarily subject throughout their closed orbits 

 to accelerations which are accompanied by a radiation of energy 

 borrowed from the internal electric and magnetic energy of the atom. 

 This radiation must be extremely small, as in the simple case of sev- 

 eral cathode corpuscles circulating at equal distances in the same 

 orbit, and can be compensated for by energy obtained from external 

 radiation. We can suppose that this continual radiation, much more 

 important naturally when the atom, as the result of external shock, 

 is displaced from its most stable equilibrium, is a cause of decay to the 

 atomic structure and which at the end of a certain length of time 

 ought necessarily to give the structure a fundamental rearrange- 

 ment, as a top falls when its rotation has sufficiently diminished in 

 velocity. A condition of instability is thus reached, the consecutive 

 rearrangement being accompanied by a violent projection of certain 

 electrified centres from the atom. This conception furnishes at least 

 an image of radioactive phenomena, and the successive transforma- 

 tions in the life of an atom, an hypothesis of which has been advanced 

 by Rutherford. It seems, however, that it is not necessary to admit 

 a probable decay of atomic structures, sensible only for radioactive 

 substances. The fact that the dispersion takes place as a function of 

 the time according to a rigorous exponential law, the quantity which 

 is destroyed in a given time being exactly proportional to the quantity 

 present, seems to indicate that the substance not destroyed remains 

 identical with itself. Perhaps the reorganization of the atomic struc- 

 ture might result from its accidental passage through a particularly 

 unstable configuration, the probability that a like configuration 

 should be reproduced being independent, in the mean, of the previous 

 history of the atom, and the mean life of the latter would be short in 

 proportion as this probability is great. 



(41) Internal Energy and Heat set Free. A very simple calculation 

 shows also that the stock of energy represented by the electric and 

 magnetic fields surrounding the electrons contained in an atom is 

 sufficiently great to supply for ten million years the evolution of heat 

 discovered by Curie in the radium salts. As it appears now well 

 established that the mean life of a radium atom is of the order of a 

 thousand years, it results that the ten-thousandth part only of this 

 reserve of energy is utilized during this especially active period in 



