: The rest mass is the same. I think Lorentz discovered what he called the longitudinal and transverse mass in around 1900. It was experimentally testing in around 1902. Einstein uses similar terminology in his 1905 paper. [[User:RSchlafly|RSchlafly]] 02:32, 25 August 2010 (EDT) | : The rest mass is the same. I think Lorentz discovered what he called the longitudinal and transverse mass in around 1900. It was experimentally testing in around 1902. Einstein uses similar terminology in his 1905 paper. [[User:RSchlafly|RSchlafly]] 02:32, 25 August 2010 (EDT) |