48 THOUGHTS ON NATURAL PHILOSOPHY. 



fore, in conceiving that a great deal of energy could 

 remain within an atom. It is even surprising that 

 a notion so evident was not formulated long since. 



Our calculation of radio-active energy has been 

 made within those limits of speed at which experi- 

 ments show that the inertia of these particles does 

 not sensibly vary, but it is possible that one cannot 

 assimilate their inertia though this is generally 

 done to that of material particles, and then the 

 figures given might be different. But they would 

 none the less be extremely high. Whatever the 

 methods adopted and the elements of calculation 

 employed velocity of the particles, calories emitted, 

 electric attractions, etc. one arrives at figures differ- 

 ing from each other indeed, but all extraordinarily 

 high. Thus, for example, Rutherford fixes the energy 

 of the A particles of thorium at six hundred million 

 times that of a rifle-ball. Other physicists who, since 

 the publication of one of my papers have gone into 

 the subject, have reached figures sometimes very 

 much higher. Assimilating the mass of electrons to 

 that of the material particles, Max Abraham arrives 

 at this conclusion: "That the number of electrons 

 sufficient to w 7 eigh one gramme carry with them an 

 energy of 6 x io 13 joules." Reducing this figure to 

 our ordinary unit, it will be seen to represent about 

 80,000,000,000 horse-power per second, about twelve 

 times greater than the figures I found for the eneigy 

 emitted by one gramme of particles with a speed 

 of 100,000 kilometres per second. 



J. J. Thomson has also gone into estimates of the 

 magnitude of the energy contained in the atom, 



