I have found "The concept of mass" by Lev Okun, (Physics Today, 1989) to be thought-provoking and informative on the subject. I return to it every time discussi

I have found "The concept of mass" by Lev Okun, (Physics Today, 1989) to be thought-provoking and informative on the subject. I return to it every time discussions of rest mass come up. Physics Today link here: http://www.physicstoday.org/resource/1/phtoad/v42/i6/p31_s1?isAuthorized=no http://www.physicstoday.org/resource/1/phtoad/v42/i6/p31_s1?... Free PDF here: www.itep.ru/theor/persons/lab180/okun/em_3.pdf‎