104 BELL SYSTEM TECHNICAL JOURNAL 



the proportion goes up rapidly with the nuclear mass of the bombarded 

 atoms.^ Both of these rules are in harmony with the remarkable 

 theory to which I alluded in the First Part — ^the theory that each 

 positive electron (together with a negative companion) springs into 

 being from a transmutation of light into electricity! It is supposed 

 that a photon transmutes itself into a pair of electrons, one of each sign. 



Fig. 1 — Tracks of an electron-pair (positive and negative) arising in argon exposed 

 to gamma-rays, and probably crekted near an argon nucleus by transmutation of a 

 photon. (M. et Mme. Joliot) 



Conservation of the net charge of the universe is assured in this 

 hypothetical process. Conservation of mass and energy is attainable, 

 for the speeds of the electrons may be such that their energies together 

 are equal to the energy of the vanished photon. I take this occasion 

 to repeat Einstein's principle, which figures so importantly in these 

 articles. The energy £ of a material particle moving with speed v 

 (relatively to the observer) is given by the formula: 



E = moil - |82)-i/2c2 = mc\ 



^ In this connection it should be noted that the source "Po + Be" emits neutrons 

 as well as photons, and while the first-named are certainly not chiefly responsible for 

 the positive electrons, they may produce some of these. Chadwick observed that 

 the rays from a " Po + B" source (boron in place of beryllium), which consist of 

 neutrons plus some photons of about the same energy as the photons of ThC", 

 evoked from lead a distinctly larger percentage of positive electrons than do the rays 

 of ThC". 



