"The universal meaning of the quantum of action", by Jun Ishiwara

Commented translation of the paper "Universelle Bedeutung des Wirkungsquantums", published by Jun Ishiwara in German in the Proceedings of Tokyo Mathematico-Physical Society 8 106-116 (1915). In his work, Ishiwara, tenured at Sendai University, Japan, proposed - simultaneously with Arnold Sommerfeld, William Wilson and Niels Bohr in Europe - the pase-space-integral quantization, a rule that would be incorporated into the old-quantum-mechanics formalism.