512 Displacement Currents [CH. xvn 



588. To sum up, we may say that experiment makes it certain that a 

 large part of the mass of the electron is electromagnetic in its origin, and 

 makes it probable that the whole mass is of this nature. If so, it is natural 

 to suppose further that the mass of the carriers of positive electricity must 

 also be electromagnetic. Thus we may conjecture, with a good deal of 

 probability, that all mass is of electromagnetic nature, so that all kinetic 

 energy of material bodies can be explained as the electromagnetic energy 

 of displacement-currents in the ether. 



REFERENCES. 



On displacement-currents : 



MAXWELL. Electricity and Magnetism. Part iv, Chap. ix. 



J. J. THOMSON. Elem. Theory of Electricity and Magnetism. Chap. xm. 



WEBSTER. Electricity and Magnetism. Chap. xni. 



On Units: 



WHETHAM. Experimental Electricity. Chap. vin. 



J. J. THOMSON. Elem. Theory of Electricity and Magnetism. Chap. xn. 



On Electromagnetic Mass: 



J. J. THOMSON. Electricity and Matter. Chap, n, or The Corpuscular Theory 



of Matter (1907). Chap. n. 



W. KAUFFMANN. Sitzungsber. d. Preuss. Akad. Wiss. Berlin, 45. p. 949. 

 M. PLANCK. Phys. Zeitschrift, 1. p. 753. 



