A flame war about entropy

Following an address by James Swinburne that was published in an extended version in The Electrician in December 1902, John Perry wrote letters to the editor published in two journals in which he objected to an inequality appearing in the definition of entropy; he demanded an equality. He also took the comments as a personal affront, since they could be seen as condemning engineering books he wrote. That began a dispute carried out in British engineering journals about the definition and meaning of entropy in thermodynamics. The extended dispute grew beyond the question of equality vs inequality and exposed uncertainty and confusion among engineers about understanding and using entropy. Several prominent physicists provided contributions either at the request of editors seeking to calm the dispute or on their own initiative. Lord Kelvin provided the terse reply: Clausius had the right definition with an inequality. Oliver Lodge provided a guide for perplexed engineers. Max Planck compared nature to a trader demanding payment in entropy. Poincaré offered a notable and distinctive definition of entropy in terms of changes of state of a system that can only proceed in one direction.